Byte Magazine Volume 02 Number 03 - Inexpensive Joystick Interfaces

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WHY SETTLE FOR LESSTHAN A 6800 SYSTEM

MEMORY—

All static memory with selected 2102 IC's a lows processor to run at its maximum speed at all times. No refresh system is needed and no time is lost in memory refresh cycles. Each board holds 4,096 words of this proven reliable and trouble - —*►

free memory. Costonly $125.00 for each full 4K memory.

INTERFACE—

Serial control interface connects to any RS-232, or 20 Ma. TTY control terminal. Connectors provided for expansion of up to eight interfaces. Unique programmable interface circuits allow you to match the interface to almost any possible combination of polar ity and control signal arrangements. Baud rate selection can be made on each individual interface. All this at a sensible cost of only $35.00 for either serial, or parallel type

PROCESSOR

"Motorola" M6800 processo with Mikbug® ROM operating system. Automatic reset and load ing, plus full compatability with Motorola evaluation set software. Crystal controlled oscillator provides the clock signal for the processor and is divided down by the MC14411 to provide the various Baud rate outputs for the interface circuits. Full buffering on all data and address busses insures "glitch" free operation with full expansion of memory and interfaces.

POWER SUPPLY—

Heavy duty 10.0 Amp power supply capable of powering a fully expanded system of memory and interface boards. Note 25 Amp rectifier bridge and 91,000 mfd computer grade filter capacitor.

DOCUMENTATION—

Probably the most extensive and complete set of data available for any microprocessor system is supplied with our 6800 computer. This includes the Motorola programming manual, our own very complete assembly instructions, plus a notebook full of information that we have compiled on the system hardware and programming. This includes diagnostic programs, sample programs and even a Tic Tac Toe listing.

Mikbug® is a registered trademark of Motorola Inc.

" d®@(S)

Computer System with serial interface and 4,096 words of memory. .$395.00

□ Enclosed is $395 for my SwTPC Computer Kit

□ or BAC #_

□ or MC

□ Send Data

Ex Date_

ADDRESS

CITY STATE ZIP

Southwest Technical Products Corp., Box 32040, San Antonio, Texas 78284

Meet the most powerful jjlC system available for dedicated work.

Yet it's only $595:

Here's the muscle you've been telling us you wanted: a powerful Cromemco microcomputer in a style and price range ideal for your dedicated computer jobs — ideal for industrial, business, instrumentation and similar applications.

It's the new Cromemco Z-2 Computer System. In the Z-2 you get all of the following for only $595:

• The industry's fastest jjl? board (4 MHz or 250nanosecond cycle time).

• The power and convenience of the well-known Z-80 MP.

• A power supply you won't believe ( + 8V @ 30A, + 18V and -18V @ 15A. That's not only ample power for a full set of cards but ample additional power for other peripherals such as floppy disk drives).

• A full-length shielded motherboard with 21 card slots to let you plug in almost any conceivable combination of memory, I/O or your own custom circuits.

• Power-on-jump circuitry to begin automatic program execution when power is

turned on.

• The S-100 bus that's widely supported by a host of peripherals manufacturers.

• All-metal chassis and dust case.

♦kit price

• Standard rack-mount style construction that's usable with a variety of cabinets and is upward compatible with larger systems. Bench cabinet optional.

• Card retainer to secure cards in sockets under all conditions.

• 110- or 220-volt operation.

DEDICATED APPLICATIONS

The new Z-2 is specifically designed as a powerful but economical dedicated computer for systems work. Notice that the front panel is entirely free of controls or switches of any kind. That makes the Z-2 virtually tamper-proof. No accidental program changes or surprise memory erasures.

(For your custom work, Cromemco will supply blank panels.)

4 MHz SPEED

Cromemco's microcomputers are the fastest and most powerful available. The 4 MHz speed of the Z-2 means you get about twice the speed of nearly any other microcomputer.

(continued <

rvm*mr 0

OVER

Full-width motherboard has slots for 21 cards.

Z-2 is supplied for rack mounting. Attractive bench cabinet shown is also available.

Heavy-duty retainer bar insures that cards won't jostle out of sockets.

That 4 MHz speed cuts running time in half— cuts your waiting time in half. Lets you do more sophisticated work that might not otherwise be practical with a microcomputer.

Z-80 GIVES MORE COMPUTER POWER

The Z-2 uses the powerful Z-80 microprocessor with its 158-instruction set, 19 internal registers, 10 addressing modes, and 16 bit arithmetic operations.

The Z-80 is widely regarded as the standard microprocessor of the future. So you're in the technical fore with the Z-2. But you can also plug in other microprocessor boards if you wish.

BROAD SOFTWARE SUPPORT

Since the Z-2 uses the Z-80, your present 8080 software can be used with the Z-2. In addition, Cromemco also offers software support including a monitor, assembler, and a BASIC interpreter.

STANDARD S-100 BUS

The Z-2 uses the S-100 bus that has become standard in the microcomputer field. Dozens of manufacturers support it with compatible peripherals.

Of course, all Cromemco peripherals such as our 7-channei A/D and D/A converter, our well-known BYTESAVER with its built-in PROM programmer, our color graphics Interface, etc., will also plug into the bus.

LOW NOISE

Cromemco engineers have been careful to design the Z-2 for reliable operation at its fast 4 MHz speed. Noise on the motherboard, for example, has been carefully minimized by a unique ground-plane design (we call it our 'Blitz Bus™'). With this bus you won't get erratic operation due to ground current noise.

RACK OR CABINET MOUNTING

The basic Z-2 is supplied in a black-anodized metal case for mounting in a standard 19-inch relay rack. A high-quality stylized bench cabinet in an attractive blue color is also available.

KIT OR ASSEMBLED

You can get the Z-2 either kit or assembled. The kit includes the Z-2 for rack mounting, the Cromemco 4 MHz microprocessor card, full-length 21-card-slot motherboard, power supply, one card socket and cardguide set, and front panel.

The assembled Z-2 includes the above as well as all 21 sockets and card guides and a cooling fan,

LOW, LOW PRICE

All who've seen the Z-2 have been surprised and impressed with its low price.

You'll be impressed, too, with its technical excellence and quality.

So see it right away at your computer store — or order now directly from the factory.

The sooner you put this advanced computer to work for you, the sooner you'll be solving problems and saving time/money.

Z-2 Computer System kit (Model Z-2K) $595.

Z-2 Computer System assembled

(Model Z-2W) ... $995.

rjj Cromemco

i n c o r p o r a t e d Specialists in computers and peripherals 2432 CHARLESTON RD., MOUNTAIN VIEW, CA 94043 • (415) 964-7400

In the Queue

iiiii

MARCH 1977 Volume 2 Number 3

Foreground

70

88

106

122

9 18 26 38 50 114

4

13

14

16

36

98, 104 102 113 130

136, 146 137 140 142 160 160

SIMPLIFIED OMEGA RECEIVER DETAILS

Hardware—Burhans INEXPENSIVE JOYSTICK INTERFACES

Hardware—Buschbach FLIGHTS OF FANCY WITH THE ENTERPRISE

Games Software—Price MULTIPLEX YOUR DIGITAL LED DISPLAYS

Hardware—Hogenson

Background

GIVE YOUR MICRO SOME MUSCLES

Hardware—Grappel REVIEW OF THE SWTPC PR-40 ALPHANUMERIC PRINTER

Product Description—Kay CASSETTE TRANSPORTS FOR THE "ROLL YOUR OWN" HOBBYIST

Cassette Transports—Freeman THE DIGITAL CASSETTE SUBSYSTEM, Part 2

Hardware—Bremeir-Rampil WHAT'S INVOLVED IN KIT BUILDING?

Construction—Frenzel TRY THIS COMPUTER ON FOR SIZE

Review—Ciarcia

Nucleus

In This BYTE

PAPERBYTES™ Forum

BYTE Goes International

Letters

A 6502 Op Code Table

What's New?

Technical Forum

Positively Baker Street

Another PAPERBYTES™ Test

BYTE's Bits

BYTE's Bugs

Classified Ads

Clubs, Newsletters

BOMB

Reader Service

BYTE magazine is published monthly by BYTE Publications, Inc, 70 Main St, Peterborough, New Hampshire 03458. Subscription rates are $12 for one year, $22 for two years, $30 for three years in North America. Second class postage paid at Peterborough New Hampshire 03458 and at additional mailing offices. Phone 603—924-7217. Entire contents copyright © 1977 BYTE Publications, Inc, Peterborough NH 03458. All rights reserved. Address editorial correspondence to Editor, BYTE, 70 Main St, Peterborough NH 03458. Opinions expressed by authors are not necessarily those of BYTE magazine.

PUBLISHERS

Virginia Peschke Manfred Peschke EDITOR

Carl T Helmers Jr PRODUCTION MANAGER Judith Havey

CIRCULATION MANAGER Manfred Peschke ASSISTANT PUBLISHER Debra Boudrieau CO-OP EDITORS Scott Morrow Dan Pagan PRODUCTION EDITOR

Karen Gregory CIRCULATION Kimberiy Barbour Cheryl Hurd

Deborah R Luhrs Carol Nyland

Deena Zealy ADVERTISING

Elizabeth Alpaugh

Virginia Peschke ART

Matthew Arnold

Noreen Bardsiey

Mary Jane Frohlich

Lynn Mato

Bill Morello SPECIAL PRODUCTS

Susan Pearne

Floyd Rehling

TYPOGRAPHY

Custom Marketing Resources Inc

Goodway Graphics

Mary Lavoie

Taimi Woodward

PHOTOGRAPHY

Ed Crabtree

Custom Marketing Resources Inc

PRINTING

The George Banta Company

Custom Marketing Resources Inc

Lennie Cashion

Larry Davis

Jeff Pratt

ASSOCIATES

Bob Baker

Walter Banks

Steve Ciarcia

Dan Fylstra

Portia Isaacson

Harold A Mauch

CLUBS, CLASSIFIED

Peter Travisano

AFFILIATE PUBLISHER

Southeast Asian Editions

John Bannister

page 26

page 9

In This HTE

Many of the possible applications of small computers involve the moving of a mechanical device. One possible way to digitally control these devices is with servomechanisms such as those used in radio controlled model aircraft. In his article, Give Your Micro Some Muscles, Robert D Grappel describes how simple it is to interface these devices with your computer to control your own mechanical devices.

Since microprocessors have hit the hobby market, one of the larger difficulties of the computer hacker has been obtaining inexpensive hardware copy capabilities. Southwest Technical Products Corp has introduced a line printer that is the answer to this difficulty. Their inexpensive impact dot matrix printer is described by Gary Kay in his article A Review of the SWTPC PR-40 Alphanumeric Printer.

page 88

The audio cassette is a kluge similar to paper tape; it works but is inconvenient. The "ideal" cassette system is completely controlled by the computer's commands, the full digital cassette recording facility. In his article on Cassette Transports for the "Roll Your Own" Hobbyist, William H Freeman takes a look at three different drives which have potential as mass storage subsystems for the personal computing experimenter.

Last month we began an article on The Digital Cassette Subsystem, by Jack Breimeir and Ira Rampil. In this issue, we continue the discussion with part 2, concerning digital data formats and system considerations.

Today's computer hobby world is a kit oriented one. In his article, Kit Building for the Computer Hobbyist, Louis E Frenzel sets forth guidelines that allow the inexperienced kit builder, the inexperienced hardware person, or the software hacker who just wants to get the basics, to construct a working computer oriented kit on the first attempt.

Navigation has come a long way since the astrolabe, as exemplified by the Omega system. In this month's BYTE, Ralph W Burhans continues his presentation of the hardware for an inexpensive Omega navigation system with some Simplified Omega Receiver Details. (The series concludes with an article on software by Richard J Salter Jr in next month's BYTE.)

About the Cover

This month's cover is by Sandra D Crandall, Narragansett Rl 02882, a first prize winner of BYTE's Computer Art Contest. When she painted her updated "American Gothic," she was completing her BFA in Art at the University of Rhode Island, and as assistant Art Department slide curator, maintained a library of over 40,000 slides. "My fiance is finishing his BS in Computer Science and is an avid BYTE subscriber from the word go," she wrote.

To interact with video games or graphic systems, it is often useful to interface devices such as joysticks to the microprocessor. In his article, An Inexpensive Joystick Interface, Thomas Buschbach describes one method that will enable you to implement the conversion process in hardware.

Over the years since the demise of the original Star Trek television series, there has been an increasing variety of people enamored with the ideas that the program had to offer. Among these people are personal computing enthusiasts who have turned these ideas into a large variety of computer games. In Flights of Fancy with the Enterprise, David Price introduces his own version of the Star Trek theme. His program, though small enough to be played on many microcomputers, allows a wide enough number of variations in play to satisfy even the most frequent users. This program is a must for Trekkies.

Steve Ciarcia owns and uses a Digital Group 8080A system. Read about his experiences and you might want to Try This Computer on for Size.

Want 16 digit BCD output for your calculator software? Need an octal display to replace your binary lamps? Read Jim Hogenson's article on how to Multiplex Your Digital LED Displays to find out what it takes to make numeric display output hardware.

■■■■reducing Sol Systems

want m your Personal computer.

Sol Termina Computer

nina Computer

Sol Systems put it all together.

One source for hardware and software.

One source for

engineered compatibility

of computer and peripherals.

That's the Sol plan.

Though the microprocessor made the powerful small computer possible, a lot of folks found out early efforts in the marketplace were selling the sizzle a lot more than the steak. After an initial investment of several hundred dollars, you ended up with some nice parts, but no memory of any kind, no I/O devices or interfaces, no display, printout or software.

The Sol plan ends all that. Processor Technology takes the position that it's far better to be right than first. So let's get down to the Sol no tricks plan.

For $995 in kit form, the first complete small computer

Standard is a basic word at Processor Technology. The Sol-20 has more standard features than any other small computer we know of. Here's what you get.

8080 microprocessor* 1024 character video display circuitry* 1024 words of static low-power RAM* 1024 words of preprogrammed PROM* a custom, almost sensual 85-key solid-state keyboard* audio cassette interface capable of controlling two recorders at 1200 baud* both parallel and serial standardized interface connectors* a complete power supply* a beautiful case with solid walnut sides* software which includes a preprogrammed Prom personality module and a cassette with Basic-5 language plus two sophisticated computer video games* the ability to work with all S-100 bus (Altair 8800/IMSAI/PTC) products.

There are no surprises. Everything you need to make it work is here. In kit form, nominal assembly time from our fully documented instructions is four to seven evenings.

Or start with the Sol-PC for just $475

You can begin your Sol system with the all on one board Sol-PC kit. It has all the

memory and interface electronics including video display, keyboard interface, audio cassette interface, all necessary software and the ability to accept the full Processor Technology line of memory and interface modules. Use the Sol-PC as the basis of a microcomputer, low cost CRT terminal or editing terminal

The Sol plan, completely expandable.

By filling the basic main frame with tailor made Processor Technology plug-in PC boards, you can really expand the computing power and flexibility of your Sol-20 Personal Computer.

New items are being announced frequently, but right now, here are some of the things you can add to your Sol-20. The ALS-8 Firmware module is an assembly language operating system to give you the power to develop and run programs. Use it to quickly write, edit, assemble, de-bug and run your own programs. Some say it's the most useful software development on the market today, but modesty prohibits.

And when it comes to add-on memory boards, you've come to the right place. We've probably got more than anyone else. Choose from 2K ROM or 4, 8 or 16K RAM. The PT 2KRO will accept up to eight 1702A or 5203Q erasable, reprogrammable memories (EPROM's) with the ability to store in a nonvolatile fashion up to 2048 eight-bit words.

Our read/write memories are the industry standards for high reliability. We know, because we have literally scores of customer letters saying "Your memory modules work and keep on working."

A full line of Sol-20 tailored peripherals

No computer can do the full job without the right set of peripheral gear. PT has

So\ liTmiii.il Computet

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sought out the best manufacturers of peripheral equipment and worked with them to give you a choice of quality so you can get the most out of your Sol-20. Choose from line and serial printers, perforated tape readers and punches, floppy disk memories, black and white or color graphics displays, A/D, D/A converters and more.

Software, the Computer Power Essential

A big part of making the first complete small computer is providing you with a wide range of easy to use, easy to obtain, low cost software. For the Sol-20, we've developed a whole group of offerings. And more are on their way.

Sol Systems Price List

(prices are net, effective Dec. 1, 1976)

SOL-10 TERMINAL COMPUTER™ Sol-PC with case, power supply and 70 key solid state keyboard.

$795/

SOFTWARE

ITEM with manual

BASIC 5 software

#2 8K BASIC New 8080 Focal TREK 80 video

game GAMEPAC 1

video games AAATHPACK video

calculator ASSEMBLER

software #1

CUTS Paper

Source cassette tape

yes ** $19.50

no $29.00 $37.00

no $14.50 N/A

no $ 9.50 $14.50

no $ 9.50 $14.50

yes $14.50 $19.50

yes $14.50 $19.50

**CUTS cassette of BASIC 5 is included FREE with all orders for Sol units or CUTS cassette interfaces. Additional cassettes available for $14.50.

Sol system owners be sure to note Sol system on your order. These special versions use less code and provide easier loading along with more convenient operation. SOLOS, SOLED and CONSOL all have provision for the special versions.

All Processor Technology software is distributed on an individual sale basis for personal use. No license to copy, duplicate or sell is granted with this sale. Each software package has been copyrighted by Processor Technology and all rights therein are reserved.

Sol Terminal Computers Kit Price

SOL-PC SINGLE BOARD TERMINAL

COMPUTER™ $475.*

SOL-20 TERMINAL COMPUTER™ all features of Sol-10 with larger power supply, 85 key solid state keyboard, fan, and five slot expansion backplane. $995.

*Sol prices include CONSOL Personality Module. If SOLED Intelligent Editing Terminal Module or SOLOS Standalone Operating System Module is desired instead, add $100. If ordered separately, personality modules are $150 each.

Mass Storage Systems

Helios II Disk System™ includes dual PerSci 270 floppy disk drive, cabinet, fan,S-100 bus compatible controller, power supply, system diskette with complete

PTDOS software

Memory Modules

ALS-8 PROM Resident Assembly

Language Operating System SIM-1 Interpretive Simulator

add-on option for ALS-8 TXT-2 Text Editing add-on

option for ALS-8 2KRO Erasable PROM module 4KRA 4096-word Low Power

Static RAM 8KRA 8192-word Low Power

Static RAM 16KRA 16384-word Dynamic

RAM

Interface modules 3P+S Parallel/Serial I/O

module CUTS Computer Users Tape

System cassette interface VDM-1 Video Display Module

$1895 $2295

Kit Asmbld.

— $425

— $ 95

— $ 95 $ 65 $ 89

$159 $195

$295 $375

— $529

$149 $199

$ 87 $119 $199 $295

See your nearest dealer or contact us directly. Address Processor Technology, 6200B Mollis Street, Emeryville CA 94608, Phone 415/652-8080.

^ g>;<~y>;

Give

Your

Micro

Some

Muscles

Robert D Grappel 148 Wood St Lexington MA 02173

A lot of proposed microcomputer applications require the computer to control various mechanical devices. Opening and closing valves, moving things, pushing, turning, etc, are not things that computers can do without help. This article describes a surprisingly easy way to turn digital signals into mechanical motion. This will make it easier to design plotters, controllers . . . anything that requires motion.

Before I was bitten by the "computerbug, " my hobby was building radio controlled aircraft. In trying to solve the problem of transferring the position of the pilot's hand to the position of a control surface on the aircraft, we modelers gradually came to use digital systems. The servomechanisms used in aircraft are very sophisticated devices. They are tiny, less than 3 cubic inches (49 cubic centimeters). They are light, less than 2 ounces (58 grams). They provide up to 4 pounds (1.8 kilograms) of thrust. Each servo requires less than 200 mA of current at 5 V. They continue to work over a wide temperature range and in conditions of extreme vibration. It seems to me that such devices would make ideal muscles for our computers. Servos are readily available, and are relatively cheap at around $25 to $50, How does one interface an aircraft servo to a micro? Would you believe three connections? Yes, it really is that simple.

You will want to use what is called a

See Sol now

The full line of Processor Technology Sol Computers, systems, software and peripheral equipment is on display now at your nearby Sol store

CALIFORNIA 1514 University Ave. Berkeley CA 94703 The Byte Shop 2559 South Bascom Ave. Campbell CA 95008 Byte Shop Computer Store

6041 Greenback Lane Citrus Heights CA 95610 The Byte Shop 16508 Hawthorne Blvd. Lawndale CA 90260 The Byte Shop 1063 El Camino Real Mountain View CA 94040 The Computer Mart 624 West Katella #10 Orange CA 92667 The Byte Shop 2227 El Camino Real Palo Alto CA 94306 The Computer Store of San Francisco 1093 Mission Street San Francisco CA 94103 The Byte Shop 155 Blossom Hill Rd. San Jose, CA 95123 The Byte Shop 509 Francisco Blvd. San Rafael CA 94901 The Byte Shop 3400 ErCamino Real Santa Clara CA 95051 The Byte Shop 2989 North Main St. Walnut Creek CA 94596

FLORIDA

Microcomputer

Systems, Inc.

144 So. Dale Mabry Hy.

Tampa FL 33609

GEORGIA

Atlanta Computer Mart 5091-B Buford Hwy. Atlanta GA 30340

ILLINOIS

The Numbers Racket 518 East Green Street Champaign IL 61820 itty bitty

machine co., inc. 1316 Chicago Ave. Evanston IL 60201

IS&R&

INDIANA

The Data Domain 406 So. College Ave. Bloomington IN 47401

KANSAS

The Computer Hut 521 N. Hillside Wichita, KS 67214

MICHIGAN

The Computer Store

of Ann Arbor

310 East Washington

Ann Arbor Ml 48104

General Computer Store

2011 Livernois

Troy Ml 48084

NEW JERSEY The Computer Mart of New Jersey 501 Route 27 Iselin NJ 08830 Hoboken Computer Works No. 20 Hudson Place Hoboken NJ 07030

NEW YORK

Audio Design Electronics 487 Broadway, Ste. 512 New York NY 10013 The Computer Corner 200 Hamilton Ave. White Plains NY 10601 The Computer Mart of Long Island 2072 Front Street East Meadow, LI. NY 11554

The Computer Mart of New York 314 Fifth Ave. New York NY 10001 Synchro Sound Enterprises 193-25 Jamaica Ave. Hollis NY 11423

OREGON

The Real Oregon

Computer Co.

205 West 10th Ave.

Eugene OR 97401

Byte Shop Computer

Store

2033 S.W. 4th Ave.

Portland OR 97201

OKLAHOMA High Technology 1020 West Wilshire Blvd. Oklahoma City OK 73116

RHODE ISLAND Computer Power, Inc. M24 Airport Mall 1800 Post Road Warwick Rl 02886

TEXAS

The Micro Store

634 South Central

Expressway

Richardson TX 75080

WASHINGTON

The Retail Computer

Store

410 N.E. 72nd

Seattle, WA 98115

WASHINGTON, D.C. area

Media Reactions Inc. 11303 South Shore Dr. Reston VA 22090

WISCONSIN The Milwaukee Computer Store 6916 W. North Ave. Milwaukee Wl 53213

CANADA

The Computer Place 186 Queen St. West Toronto, Ontario M5V 1Z1 Trintronics 160 Elgin St. Place Bell Canada Ottawa, Ontario K2P2C4 First Canadian Computer Store Ltd. 44 Eglinton Ave. West Toronto, Ontario M4R LAI Pacific Computer Store 4509-11 Rupert St. Vancouver, B.C. VSR 2J4

!6-20mS

I

ImS (MINIMUM)

J

.UP TO ImS (MAXIMUM)

Figure 1: Timing diagram of the waveform that is needed to drive the servomechanism. The pulses are from 16 to 20 ms apart in time, and have a pulse width of 1 to 2 ms. This type of timing can be accomplished using your computer's internal clock as a reference in timing loopst or through a programmable real time clock.

three wire servo which is the modern type unit. These run on regulated 5 V supplies. That takes care of two of the necessary connections. The third lead is the input signal. This is a TTL compatible signal, which can be driven from one bit of a typical output port. We will use software to generate the proper waveform at this bit. Since each servo requires only one output bit, a typical byte port can drive up to 8 servos.

Servos are really pulse width feedback

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Notes on Trying Robert's Idea for Muscles by Carl Helmers, editor

Using the servo we bought to take the picture of photo 1, / wrote the program shown in this listing to illustrate the operation and test out the characteristics of the device. The program is written for my homebrew 6800 system, which has parallel interface ports at hexadecimal addresses 150 to 157 in memory address space. The PIA port at locations 150 and 151 was used for this experiment, with some binary indicator lamps at location 14F used to tell what the current state of the command parameter was. This program uses a subroutine in my monitor called MILI which is a timing loop returning to the calling point 1 millisecond after entry. The interpuise space was arbitrarily set at 250 ms (it worked) in order to allow observation of what was happening

Continued on page 34

Photo 1: A typical model aircraft servo, which we purchased at a local hobby shop in Greenville NH. The price of this unit was about $45, and the only documentation we could find on it, the catalog, said it could exert 5 pounds of force, presumably at the limit of the lever arm provided by the standard bell cranks and connection wheels which came with it. We took it apart after photography and found a gearbox with several gears, the motor, potentiometer slaved to the main output shaft, and electronics. Although the printed circuit board internal to the device had "made in japan" marked on it, the actual integrated circuit was clearly a result of international trade — it was marked "Texas Instruments." After reassembly, it was tried out with the program shown in the box accompanying this article, using a PIA port at address location 0150 (hexadecimal).

units. The input is a pulse with a carefully controlled width. The servo contains an electric motor, a gear train, a feedback potentiometer connected to the gearing, and some fairly sophisticated electronics. In modern servos, all the electronics is contained in a custom integrated circuit. The circuit generates an internal pulse every time it receives an input pulse. The internal pulse width is controlled by the feedback pot. The circuit then compares the pulse widths. If they match, then no current goes to the motor. If they do not match, then current is fed to the motor and it drives the mechanics, together with the feedback pot, in the appropriate direction until the pulse widths again match. By feeding pulses in a rapid stream into the servo, it will appear to track the varying pulse width.

Just about every servo sold for use in model aircraft expects pulse widths varying between 1 and 2 ms. Most servos use positive going pulses, but there are a few servos around which require negative going pulses. The pulses should be repeated every 16 to 20 ms. The repetition frequency is not critical. The servo will run from extreme to extreme in about 0.5 s. To drive the servo, one then needs to generate a waveform like that in figure 1. This can be done with timing loops, interrupts or programmable timers. Even the slowest processor can handle this task.

Model boats, and some aircraft, use electric power plants. The same type of controls can be used to vary the speed and direction of electric motors. For readers interested in controlling motors, and other high power devices, I would recommend the circuits published in RCM} (Radio Control Modeler). Page 166 in the April 1976 issue shows a circuit using the integrated circuit from a servo and two external transistors to control a 20 A motor from full stop to full speed. Page 12 of the September 1976 issue shows a similar circuit which has the added feature of forward and reverse control. Circuits like these can also control other loads, like lights or heaters. This is fully proportional control, not just on and off.

Now there is no excuse for not building that robot you were thinking about. You can use servos to control your tape cassettes by pushing the buttons under computer control. Using two servos, one in the X direction and another in the Y direction, a pen plotter can give your computer a hard copy graphics capability. There are hundreds of exciting possibilities. I hope to read of some of them in these pages soon,"

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PAPERBYTES™ Forum

Machine readable printed software is an exciting subject. Numerous comments have been received from various individuals regarding the idea of machine readable printed software as described in the November and December 1976 issues of BYTE. These are excerpts from various fetters which often covered other topics as well:

Multiple Synch Characters . . .

Several people have suggested that the format should contain multiple SYN characters. Here are a couple of examples of the comments:

1 have a few comments on the proposed standard for machine readable printed data. (My forte is not building bar code readers, but I do have some experience in high speed data transmission.) In the proposed frame layout I would suggest duplicating the SYNCH character at least one more time, and possibly a couple more times. The reasoning is that even if the timing marks are included (which I don't think were in the December samples) the adaptive algorithm must establish "bit synch" to extract the bits correctly, and then it must establish "character synch" to insure it has gotten the character boundaries correct. In data transmission schemes, usually two or four synchs are used depending on whether the synch pattern is to establish only character synch or both character and bit synch. The modulation schemes you have presented seem to have enough transitions in them to get bit synch, so four synchs probably aren't needed. But the algorithm would be a lot more sure of what is going on if there were at least two synchs: one to get synched, and one to check the synch. I think this is particularly important considering the data following the synch is the checksum. Slop or jitter from the startup of the human hand could be particularly damaging here. A few extra synchs thrown in could solve that potential problem.

Maybe I am trying to make this all too complicated, but my background is one of insuring robustness in protocols. The bar code wand reader experts probably have a better feeling than I for things like this.

MikeO'Dell

University of Oklahoma

Information and Computing Sciences

601 Elm, Rm 926

Norman OK 73069

Another reader suggested putting a second S YN character at the end of the frame in order to allow scanning in either direction, a sentiment which was echoed by Tom Plttman of Tiny BASIC fame. But using the sparse format shown in the examples in this issue [or format (c) of December BYTE, page 17], the frame capacity is only about 26 to

13

32 data bytes, depending on length, so a 3 to 4% penalty in capacity is required. Also, the main advantage is to allow sweeps in both directions, which for manual scanning may not be particularly important since the rhythm of operation has to be interrupted by repositioning the guide straightedge between each swipe.

Printed, Machine Readable Braille?

Totally unrelated to our bar code representation for data, but nevertheless interesting, is this letter from C R Conkiing Jr, and his accompanying sample.

The sample is a short segment of the text, reproduced here twice the original size, which was a test occupying two sides of a letter size sheet of enameled paper.

I was interested in your thoughts on using ink print to transmit digital information. I have enclosed an ink printed sheet of paper which was printed using standard offset methods. The paper contains a complete pocket paperback size book. I must say, however, that it is in grade 2 Braille which uses contractions, as in speed writing. The Braille code is a 6 bit code, and the paper is encoded to drive a mechanical Braille cell to reproduce the data.

Why it was done is a long story. Why it was never completed is even longer. One of the reasons that it was never completed was that we had no luck

Continued on page 82

Editorial

BYTE Goes International

by Carl Helmers

Accompanying this editorial is a letter from an Australian reader, Kevin C Barnes of Five Dock, New South Wales. He's writing on the conditions of the small computer person in Australia circa September 1976. We held onto the letter until it was possible to announce an arrangement which should help promote and build an indigenous small computer industry in Australia: the new Far East Asian editions of BYTE magazine.

When BYTE first began circulation, an

electronics engineering consultant named John Bannister, a native of Sydney, Australia, subscribed nearly instantaneously when he heard about it from an American friend. But he soon ran into a problem which plagues all individuals on the end of a long international supply chain — it takes time and patience to await BYTE (or any US goods, for that matter) in Australia, which is

Continued on page 62

Are Logic States Inverted Down Under?

Here are just a few notes that might be of interest to your readers about conditions in Australia. Interest in computing is just about to happen down here. Both national electronics magazines, Electronics Australia and Electronics Today International have just (July 1976 issue) started to talk about microprocessors. They have started by reviewing the different evaluation boards available. But neither magazine has published any construction articles as yet on microprocessor based microcomputers. (EA did design and publish an 8 bit processor back in the end of 1974 and beginning of 1975, but it was a serial processor which did not gain the popularity of the present microprocessor systems. That processor, the EDUC-8, was built using TTL MSI and SSI chips and had a limited memory of 256 locations. In fact EA was beaten to the honor of being the first to publish a computer plan by only a few weeks by Radio Electronics' publication of the Mark 8.)

Commercial interests now have a number of American designed and built systems offered for sale, but unfortunately these people do not yet carry much stock. MITS equipment is offered down here by a company called WHK of Melbourne, and the proprietor has published a rather impressive catalog with all the MITS hardware and software listed. JOLT is also being advertised as well, although mainly through the trade journals. EPA's Micro 68 also has been offered for sale and the agent has at least one in stock which he is willing to lend to people to look at and play with.

I and three other people have formed a small club and have three systems operating, using the 6800, 8080 and the SC/MP chips. They have been built around evaluation boards. We also have an ASR-33 and ASR-38 Teletype and

our big project at the moment is a floppy disk. Our small project of the moment is a PROM programmer to program 1702s. In my conversations with various integrated circuit manufacturing company representatives, I've gained information that a good proportion of the sales here have been to individuals, not companies, and that many boards bought by companies have been for individuals within the companies and not for particular company projects [standard practice in the US, too . . .CH].

Also very annoying is the rather high price markup on the hardware by the time it reaches Australia. The Intel 8080 Microprocessor System User's Manual for instance has sold for $20 even though it is marked $5, while the Altair 8800A sells for $619 Australian ($740 US currently) for the basic kit with no extra boards. Well, I hope this has been of interest.

Kevin C Barnes

71 Barnstaple Rd

Five Dock

New South Wales 2046

AUSTRALIA

Thanks for your comments, Kevin. By the time this letter is in print, it will be part of the third issue of our new Australian English language edition of B YTE, so with any luck you'll soon start to find some increases in personal computing activity in your vicinity. Until there is local manufacture, there is no way you can beat the price penalty, as nearly as I can project: Shipping costs time and money. When a product is dear, whether through distance or natural scarcity, Adam Smith and Co long ago predicted the price would rise. I understand from John Bannister, however, that at least you don't have to pay an exorbitant import tariff as our Canadian friends do.

14

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Letters

8080 TRICKS AND FAST OPTICS FOR ISOLATION

In the November 1976 letters column, reader Bennett asked for an easy way to do an arithmetic shift right using the 8080. Try RLC, RAR, RAR; only three bytes, and the carry bit ends up the same as with SRA A on the Z80.

By the way, if anyone wants to try an optically coupled video interface to a television, look at HP's 5082-4360 optically coupled logic gate. It's rated for 10,000 bits per second and costs $6.30 in unit quantity. Cheaper optical couplers can handle sync and, if necessary, an on/off control, but the HP device is the first one I've seen that looks fast enough to handle video frequencies. Using a separate device for sync avoids critical biasing adjustments to make a single device operate in the linear mode. With separate devices, the video and sync mixer goes on the output side of the devices. Frequency response can go down to DC if you can avoid upsetting the television's video stage bias without using a DC blocking capacitor.

Robert F Miles

242 Abingdon Rd NW

Lenoir NC 28645

OOPS . . . SUPPLIES GONE

After reading the "An Item of Interest" article in the September issue of BYTE (page 100), I wrote to SWTPC for the June 1976 newsletter. Butthe newsletter is not in print anymore.

Is there any way I could get a used or old June 1976 newsletter? Piease respond.

Robert Leong

705 N Linden Dr

Beverly Hills CA 90210

WANTED: ELIZA FOR THE

SMALL COMPUTER

Many years ago I had a dialog (my first online experience!) with a computer that conversed like a psychiatrist, selecting phrases from my input and feeding them back in new context or, if nothing good suggested itself, injecting a random phrase such as "how did you feel about your father?". It was called the ELIZA program, because it learned from its input. According to one article I have read, it was originated at MIT.

Now, after considerable timesharing, I am a subscriber to BYTE and am buying an Altair 8800a on the Kit-aMonth plan. Is anyone in BYTEIand familiar with the software for ELIZA? In particular, does anyone know of a ver

sion suitable for small machines? I'll try to reinvent it if I must, but it seems silly to do so.

John P AureMus

2568 10th Av W

Seattle WA98119

ELIZA is a program created by Joseph Weizenbaum at Massachusetts Institute of Technology, which has since spread somewhat widely - in ways not necessarily consistent with its creator's goals. See BYTE's review of Weizenbaum's book, Computer Power and Human Reason, on page II, January 1977, The book is highly recommended reading for any intellectual. As to whether detail implementations of ELIZA style programs can be found, maybe a reader with academic connections can enlighten us.

THAT'S THE RIGHT IDEA ...

I'd like to give my support to Charles Wortell's entry to the Programming Quickies column [December 1976, page 132]. A few months ago I thought of presetting memory of my 6800 system to SWI (hexadecimal 3F) to catch wayward programs. I'd like to suggest the following to anyone considering a ROM operating system for a 6800: I've replaced the MIKBUG monitor in my SWTPC 6800 with a PROM monitor that initializes memory to SWI. This is only done on power up reset and not on subsequent resets,

I've changed all interrupt vectors to addresses in the processor board RAM. This allows faster interrupt service and frees the SWI for alternate uses. As an added bonus an unexpected interrupt from IO will cause a register print just like SWI.

I'd welcome correspondence from readers considering this and other routines I included in my monitor.

Leo Taylor

18 RidgeCt W, Apt 21C

West Haven CT 06516

You've got the right idea with respect to custom/zing and extending monitors. I've done a similar thing in my own machine by writing a monitor program much more capable than MIKBUG. How'd you like to start a 6800 systems programming special interest group? . . . CH

ALTAIR WORD PROCESSING NEEDED

I am interested in using my Altair 8800 to produce clean letters and reports from text entered through a keyboard with editing capabilities. Is there anyone out there who has an Altair compatible software package who can help me?

Also I'd like to inform you that we have formed a Stony Brook Homebrew Computer Club, which is both hardware and software oriented. We have friendly

and informal meetings and access to various simulators and cross-assemblers on the school computer. Members have their own systems to demonstrate and discuss (8080 and 6800).

Ludwig Braun

Professor of Engineering

State University of NY at Stony Brook

Stony Brook NY 11794

Text editing is one area where we expect to use our office Altair, among other things. Try writing in 6 months or a year if you haven't found a source by then.

YE OLDE BOARD SWITCHE MANOEUVRE

The following is a simple fix 1 found for a crashing Altair 8800. The symptom was apparent false jumps when loading and operating 12 K BASIC for a few minutes. These errors wiped out parts of the IGaded software, outputting "syntax" errors, garbage or nothing. The fix was to move the processor card to the center of the case (near the fan), away from other boards, and to tape (double back sticky) an aluminum foil (~i x 2 inch) heat sink (convection cooled) onto the SN74123. No problems have occurred since.

Dr F R Ruckdeschel

Principal Scientist

Xerox Corp

PCDD/P&MS/EDPA

800 Phillips Rd

Bldg 1 29

Webster NY 14580

WANTED- 6502 USERS

I would like to say that I enjoy your magazine very much, and look forward to it every month. It always seems to have the articles I am looking for, and they are always entertaining.

I am presently bringing up a 6502 on an OS I superboard and am interested in speaking to anyone with a micro, especially a 650x series computer. If anyone has a monitor that they think is really great, or at least perfect, please give me a call or drop me a line. My phone number is (613) 692-3786. Ask for Kevin.

Kevin Szabo

Box 86, Hillcrest Dr

RR 1, Manotick, Ontario

CANADA K0A 2N0

PAGING WITH AN 1802

First of all, thanks for coming up with a computer magazine for the experimenter just when I needed it.

In regards to the editorial "The Address Space Saturation Problem" by Carl Helmers in your November 1976 issue, page 16, I would like to make a suggestion. The RCA Cosmac 1802 microprocessor, which was used in the recent

Continued on page 94

16

Print Your Heart Out

With help from the Digital Group, naturally.

Now, that small computer system you own or have been considering for personal or business use suddenly becomes a lot more usable—with the addition of a full-size impact printer from the Digital Group. A printer designed for small computers that need big output (like yours).

With the Digital Group printer, you can print your heart out...and it won't cost an arm and a leg. The Digital Group printer is available for less than $500. That's right—$500.

Just look at these specifications:

• Fast—120 characters per second

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• 12 characters per inch horizontal

• 6 lines per inch

• Makes up to 4 copies simultaneously

• Character set and pitch variable under software control—double width characters, etc.

•5x7 character matrix

• Ribbon has built-in re-inkers for a life of 10,000,000 characters

• Paper can be either a standard 8V2-inch roll, fanfold or cut page

• Interfaces to 8-bit parallel ports

There are lots of capabilities and outstanding features of the Digital Group printer...and (as always) the best news is our price. Kit prices start as low as $495 for the printer and interface card. It simply can't be beat.

Find out all the facts about the Digital Group printer now. Just fill in the coupon below or give us a call for the details. We think youTl find a place for our printer in your system ... and in your heart.

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A Review of

Photo I: The PR-40 dot matrix printer as assembled from the kit distributed by Sou th west Technical Products. The printer is not enclosed in a case but is mounted on a black a nodi zed aluminum chassis with overall dimensions of 9.63 by 10.50 by 8.75 inches (24.45 cm by 26.67 cm by 22.23 cm).

the SWTPC PR-40 Alphanumeric Printer

Gary Kay

Southwest Technical Products Corp

219 W Rhapsody

San Antonio TX 78216

Ever since the microprocessor's introduction, computer hobbyists everywhere have been searching for a low cost alphanumeric printer. One place the search can stop is at the unit presented here: a 5 by 7 dot matrix impact printer. It prints the 64 character upper case ASCII set with 40 characters per line at a rate of 75 lines per minute on standard 3.875 inch (9.843 cm) rolls of adding machine paper, as shown in figure 1. One complete line is printed at a time from an internal 40 character first in first out buffer memory. Printing takes place either on receipt of a carriage return or automatically whenever the line buffer memory is filled.

The printer can accept character data as fast as one character per microsecond (until

the buffer is full) or as slow as you wish to send it. The printer's seven parallel data lines are TTL compatible and may be enabled by a single data ready control line or by separate data ready and data accepted handshake control lines. This universal approach makes the printer compatible with all computer and terminal systems having an eight bit parallel interface port; including, of course, the SWTPC 6800 and MITS Altair 8800 computer systems.

The printer mechanism is attached to a black anodized aluminum chassis with front trim panel which houses the circuitry including its own 120 or 240 VAC 50 to 60 Hz power supply circuit shown in figure 2, making the printer's overall dimensions 9.625 by 10.50 by 8.75 inches (24.45 by 26.67 by 22.23 cm).

The Mechanics

The entire design, shown in photo 2, is based on a simple and reliable print mechanism intended originally for point of sale

18

Figure 1: Example printout demonstrating the type of characters that are generated by the PR-40 dot matrix printer. The printout is the width of readily a vol fable 3.8 75 inch (9.843 cm) adding machine paper. The test program of listing I generated this printout.

! "«KA'<)*+, -./B1234S6789 ; <=>? tffiEiCDEFGHIJKLMNCPuRSTUVUXVZCMt 1 "#*'.'& '"0*+, -. /0122456789: ; <=>? @flBCDEFGHIJKLMNOPQRsTUVUXVZ[\]t ! "**U "()*+, -. /S123456789:; <=>? eflBCDEFGHIJKLMNOFQRSTUVWKVZCMt ! "#$v&-()*+,-, /0122456789: ;<*=>? GRBCDEFGH IJKLMNOPQRSTU VUKVZ C Mt ! " *ra. yO*+, -. /012S456789:; <C=>? @RBCDEFGHIJKLHNOP0P.STUVWXV2[\3t 1 "#«& '<>*+, -. /012J456789: > <=>? eRBCDEFGHIJKLMNOPQRSTUVWXVZC\]t ! *UY.&' ()++-- -. /01224567S9:.; <»'•' @flBCDE F GHIJKLMNOPQRST UVHXVZ[\]t 1 "#*^y <)*+,-. /012S456789: i <=>? i?HECDEFGHIJKLMNuPGRSTUVW>:vZ[\]t ! " *$'/.& -' ()*+.. -. /812J456789: ; <»? GflBCDEFGHIJKLMNOPCiRSTUVWXVZCSlt

terminal use. The printed characters are formed by moving the print head horizontally across the paper while selectively energizing solenoid driven print wires on the head which strike an inked ribbon and imprint dots on standard adding machine paper. All seven of these solenoid driven print wires converge at the tip of the print head in a vertical line which is perpendicular to the horizontal direction of movement of

a

the print head. By selectively firing the print wires, 5 dot wide by 7 dot high characters are printed as the print head moves across the paper, A one dot time spacing is left for separation between the printed characters. This method of printing characters is not new but the method of moving this wire impact print head is unique. Rather than using dual motors, clutches, timing bars and the other hardware usually associated with

£^> +40VDC

O GND2

O GND I

^—, MOTOR < I CONTROL

Figure 2: The schematic diagram of the power supply circuit for the PR-40 printer. This power supply can be run on either 120 or 240 VA C depending on whether the primary winding is wired in parallel or series. The power transformer, Tl', has a 120, or 240 V primary; 32 V @2A, 12.5 V @J A center tapped, 120 V @200 mA center tapped secondaries. As can be seen in the diagram, the printer motor is triac controlled, taking its on and off states from the position of the printer head on the page. All resistors are measured in ohms and are 0.25 W unless otherwise stated.

19

A Printer Testing Program

The printer diagnostic program of listing 1 has been written to test and debug the SWTPC PR-40 printer when it has been interfaced to the SWTPC 6800 computer system through one of the MP L parallel interface boards. It is assumed that before loading this program, the rest of the system is functioning normally with no problems. The program itself uses 60 words and is loaded within the 128 word programmable memory used by the MIKBUG® operating system on the MP A microprocessor and system board. A program may reside in external programmable memory simultaneously with the diagnostic loaded within the 128 word programmable memory, or the diagnostic may be run with no MP M memory boards installed on the system at all. The diagnostic may be loaded either from tape or instruction by instruction using MIKBUG starting from hexadecimal address A014 through A024 and then from hexadecimal address A048 through A072. The address of the MP L parallel interface board feeding the printer must be set using MIKBUG to load the hexadecimal address of the selected port into hexadeci

mal memory locations A002 and A003 with the most significant byte going into A002 and the least significant byte going into A003. The starting address locations of the interface ports are given in table 1.

Since the program counter is set when the program is initially loaded, the diagnostic is initiated as described in the "go to user's program" section of Engineering Note 100. Once initiated, the program can be stopped only by depressing the reset button. The program may then be restarted after resetting the program counter to hexadecimal A04A as described in the "display contents of processor registers function" section of Engineering Note 100.

The diagnostic works by sending out an ASCII carriage return, hexadecimal OD, followed by hexadecimal ASCII characters 21 through 3F followed by another carriage return 0D, followed by hexadecimal ASCII characters 40 through 5E inclusive, repeating itself until stopped with the reset switch.

Each character is output to the printer by first storing the ASCII character's bits 0 through 6 on output lines 00 through 06 of the selected MP L

Listing 1: A debug and test program written for a 6800 type system with MIKBUG. The hexadecimal address of the selected port is loaded into memory locations A 002 and A 003 which are referred to by PARA DR. The program counter is initiated at the beginning of the program. The program sends out a carriage return, hexadecimal ASCII characters 21 through 3F followed by a carriage return, followed by hexadecimal ASCII characters 40 through 5E, and repeated indefinitely.

Address

Op

Operand

Label

Mnemonic

Commentary

A014

A7

00

OUTCHR

STA A 0,X

PARADR: = A;

A016

C6

37

LDA B #37

\ PARADR+1:=37; J [data ready port]

A018

E7

01

STA B 1,X

A01A

C6

3F

LDA B #3F

) PARADR+1:=3F; y [data ready port]

A01C

E7

01

STA B 1 ,X

A01E

6D

01

LOOPS

TST 1 ,X

check if data accepted signal received;

A020

2A

FC

BPL LOOP3

if signal not present go to LOOP3;

A022

E6

00

LDA B 0,X

else B:= PARADR

A024

39

RTS

return;

A048 A049

A0

4A

MSB LSB

5- [program counter]

A04A

FE

A0 02

START

LDX PARADR

X:= PARADR; [IO port address]

A04D A04F

C6 E7

FF 00

LDA B #FF STA B 0,X

| PARADR-FF;

A051 A053

C6 E7

3F 01

LDA B #3F STA B 1,X

| PARADR+1:=3F;

A055

86

0D

FSTLIN

LDA A #0D

r output carriage return;

A057

8D

BB

BSR OUTCHR

A059

86

20

LDA A #20

A:=20;

A05B

4C

LOOP1

INC A

A:=A+1;

A05C

81

40

CMP A #40

compare A to 40;

A05E

27

04

BEQ NXTLIN

if A=40go to NXTLIN;

A060

8D

B2

BSR OUTCHR

goto OUTCHR;

A062

20

F7

BRA LOOP1

go to LOOP1;

A064

86

0D

NXTLIN

LDA A #0D

> output carriage return;

A066

8D

AC

BSR OUTCHR

A068

86

3F

LDA A #3F

A:=3F;

A06A

4C

LOOP2

INC A

A: = A+1;

A06B

81

60

CMP A #60

compare A to 60;

A06D

27

E6

BEQ FSTLIN

if A=60go to FSTLIN;

A06F

8D

A3

BSR OUTCHR

go to OUTCHR;

A071

20

F7

BRA LOOP2

go to LOOP2;

parallel interface port, then bringing the normally high data ready line low via interface output control line C2 for at least 1 jus, then returning the line high again. The data must be held stable on the interface output lines, however, until the printer acknowledges data receipt by bringing its normally high data accepted line momentarily low and then high again. This latter low to high transition signifies that the printer has accepted the character. The MP L control line C1 fed by this line has been programmed to see the low to high data accepted transition and responds by allowing the program to output the next sequential ASCII character.

To set the printer's line width adjustment, you should use MIKBUG to change the data in hexadecimal memory locations A056 and A065 from 0D to 00. This will eliminate the transmitted carriage returns and force the printer to print a full 40 column line. The line width control should then be adjusted for symmetrical margins. The characters will still be printed sequentially but will not be identical from line to line.

Do not operate the printer more than a minute or so while running this diagnostic. Continuous printing of full length lines with no spacing between characters overheats the solenoids on the print mechanism which may decrease its operating life.

If you are using the SWTPC PR-40 printer with the SWTPC 6800 computer system, you may use the OUTCHR subroutine listed from address A014 through A024 in the PRNTST diagnostic within your own program for outputting characters to the printer. The index register must be loaded with the starting address of the MP L parallel interface board feeding the printer. The character to be printed must be loaded into accumulator A and the contents of accumulator B are destroyed during the subroutine.

Never install or remove the interface board when the system is powered up. Doing so is not only hazardous to the equipment, but bypasses the normal power up sequence required by the internal registers within the 6820 integrated circuit in order to guarantee proper operation."

Note: MIKBUG Motorola Inc.

is a trademark of

Table I: Hexadecimal starting addresses of the parallel IO port interfaces used by MIKBUG.

Port

Address in Hexadecimal

IO0

8000

IO 1

8004 (reserved for control interface

0

I0 2

8008

I03

800C

I04

8010

IO 5

8014

I06

8018

IO 7

801 C

20

.

Si

this type of print head, this printer rotates a long cylinder just beneath the print head. The length of the cylinder itself is a little longer than the head's printing width on the paper." The cylinder has a uniform cyclic zigzag track formed on its outer circumference, running from the left side of the cylinder to the right side and then back to the left again. A small projection on the bottom of the print head rides in this track so that as the cylinder rotates, the print head moves back and forth from left to right. This technique moves the print head across the paper at a constant velocity except for the extreme ends, where nothing is being printed. This approach greatly simplifies the electronics needed to drive the printer since no head positioning circuitry is necessary. The cylinder itself is turned by an AC motor

on the lower right hand side of the print mechanism. (See photo 1.) A small ribbed nylon belt interconnecting the two rides on gear teeth of both the motor and cylinder. Also attached to the right side of the cylinder is a cam that actuates a roller arm microswitch riding on the cam. This is how the printer's electronic circuitry senses the start of line position of the print head. On the left side of the cylinder is an eccentric driven pawl arm that advances the paper one line for each revolution of the cylinder which is the same as one cycle of the print head.

Let's go through a single cycle of operation of a printed line where we will first assume the head is in rest position just left of center. When a line print command is initiated by the control circuitry, the motor

Photo 2: This photograph displays the mechanical parts of the PR-40 printer. The seven solenoids can be seen to converge in a line at the print head. The positioning mechanism for the printing head is seen as the spiral groove under the head mechanism.

21

s

4.7K /V^SaOl/iFl »TR'G G"

2N52IO jjj

ICI7 7805

_j—^ MOTOR ~L^> CONTROL

f5V

J

;HtH ted ,

starts and the head begins to move from the center position toward the far left side of the printer where the head reverses direction. This nonprint dead zone gives the motor, cylinder and print head time to attain full speed. As the head begins its movement from left to right, the cam actuated microswitch opens telling the electronic circuitry to start sending solenoid driving pulses for the character. Somewhere before the print head reaches the far right hand edge of the paper, the solenoid pulses will cease while the head continues to move. When the head reaches the right end of its travel, it will mechanically reverse direction and begin to move back toward the center of the printer. During this return movement, the pawl arm will rotate the platen one line for the line feed. The motor is then turned off just to the left of center where it started originally. With our controller for this mechanism, character data is not accepted by the printer's circuitry during an actual print cycle; however, feeding continual print data from a computer to the printer may take place so fast that the print motor may never appear to stop between repeatedly printed lines although it actually does.

The operation of the printing ribbon used on the unit is also amazingly simple. A ratchet technique not only advances the ribbon incrementally for each cycle of the print head but automatically reverses it when it reaches the end of one of the two spools.

The Electronics

The electronic circuitry designed to drive the print mechanism can vary from nothing but motor and solenoid drivers constantly serviced by the microprocessor to a fully self-contained hardware control unit with

Table 2: Power pins for the circuit of figure 3.

Number Device +5 V GND -5 V

28

IC1

3351

26

IC2

5241

12

IC3

7407

14

7

IC4

7490

5

10

IC5

555

8

1

IC6

74121

14

7

IC7

7407

14

7

IC8

7474

14

7

IC9

7420

14

7

IC10

555

14

8

IC11

7400

14

7

IC12

7404

14

7

IC13

7430

14

7

IC14

7400

14

7

IC15

7402

14

7

IC16

7400

14

7

IC17

7805

3

IC18

7474

14

7

-12 V

27 23,23

memory needing only 7 bit parallel ASCII data and a data ready strobe control line from the computer. The printer electronics of the PR-40 fits into the latter category. The PR-40's controller has its own 40 character first in first out memory allowing the computer to send character data at whatever speed it wishes. The entire line is printed upon receipt of a carriage return, hexadecimal OD, or automatically whenever the 40 character line buffer has been filled. All control characters with the exception of a carriage return are ignored by the printer. They are not stored in the buffer line memory since they cannot be printed anyway. Repeated line feeds are initiated by sending repeated carriage return control commands. Since the controller generates upper case ASCII characters only, all lower

Photo 3: A view from the bottom of the PR-40 impact printer displaying the electronic circuitry of the system. The circuit board at the top left of the picture is the circuit for the power supply as described in figure 2. The circuit at the bottom of the picture is the electronic assembly for the print head driver. The large chip at the bottom left of the picture is the first in first out memory chip. The IC chip directly above it is the read only memory character generator.

23

The PR-40 alphanumeric printer is manufactured by Southwest Technical Products Corp} 219 W Rhapsody, San Antonio TX 78216. It is sold in kit form only. The kit number is #PR-40 for $250 post paid in the United States. The kit includes the print mechanism, chassis, circuit boards, components,

power supply, assembly instructions, one ribbon and one roll of paper.

case characters sent to the controller are transposed to their upper case equivalent before printing. The printer's line buffer memory is automatically cleared by a hardware power up reset circuit when printer power is first applied. The printer's triac controlled motor is powered by a 120 VAC secondary on the power supply's power transformer, as shown in figure 2. This not only provides power line isolation but allows the entire unit to be run on either 120 VAC or European 240 VAC power systems since the power transformer has two primary windings which may be either parallel or series connected.

The seven ASCII parallel data input lines, data ready, and data accepted control lines are all TTL compatible. The inputs represent a maximum of two standard TTL loads while the data accepted output will drive ten standard TTL loads. Data is presented to the printer by storing the selected ASCII data on the seven data input lines and strobing the normally high, logic 1, data ready input line low. This line should go low, logic 0, for at least 1 fds and when it does the normally high data accepted will also go low. The character is not actually loaded until the data ready input is returned to its normally high state. The data accepted line will then normally return high as well, indicating that the character has been loaded. Ho.wever, when loading the 40th character on a print line or a carriage return command, this data accepted line will not return high until all the previously stored data has been printed and the printer memory is ready for more data. The PR-40's printer controller will ignore all data sent to it while the data accepted line is low. So you will usually want to make sure the data accepted output line is high before sending the controller more data to be printed.

If you are careful not to output data faster than one character per us and allow a minimum one second delay before sending data after sending a carriage return or the 40th character of each line then you may avoid using the data accepted line altogether. However, using the data accepted line will give your system the fastest possible print speed.

How It Works

All ASCII character data is presented to the first in first out memory, IC1, through hex inverter and buffer, IC12. NAND gate IC14A makes any necessary conversions from lower to upper case characters. 8 input NAND gate IC13 monitors the incoming ASCII data in search of a carriage return, hexadecimal 0D, control command. If it

decodes a carriage return it will prepare normally high control flip flop IC8A to go low on the falling edge of the data ready control signal. NOR gate IC15A decodes all control characters and along with IC15B inhibits any control characters from being loaded into the buffer memory. NAND gate IC9A is responsible for generating the data accepted control output whenever data has been accepted by the buffer memory or acknowledged by the control character decode logic. It also inhibits the data accepted output while the printer is in the process of printing a line.

Control flip flop IC8A's Q output is high when the printer is in the idle state. A buffer memory full signal decoded by NOR gate IC15D or a decoded carriage return command by IC13 resets this flip flop low which turns the printer's motor on through transistors Q1 and Q2 located on the power supply board which starts a line print sequence.

When the print head advances to the start of line position, the roller arm microswitch changes states which flips RS latch NAND gate (C11D low which allows free running oscillator, IC10, to feed divide by 2 flip flop, IC8B. This divide by 2 feeds both the dot counter, IC4, and solenoid timer, IC6. This solenoid timer is used to set the on time of the printer's solenoids. If set too long, the solenoids will overheat; if set too short, the printed lines will be too light. An on time duration of 400//s is the best compromise setting. Decode counter IC4 has its B and C outputs tied back to its zero reset inputs forcing it to become a modulo 6 counter. As the counter progresses from 0 to 4 inclusive, the selected character lines are decoded by the read only memory, IC2, using the ASCII data fed to it by the buffer memory, IC1, and fed onto the solenoids through buffers IC3 and IC7 and Darlington drivers Ql and Q7. Counter state 5 is decoded by the read only memory as a blank for the one dot space necessary to separate the printed characters. In the latter phase of the five count the memory buffer is shifted, the counter resets, and the sequence repeats. When the memory buffer finally empties, the read only memory is disabled and blanks the output for the rest of the print cycle. When the still moving print head reaches its normal rest position, the roller arm microswitch again changes states. This time RS latch NAND gate IC11C flips low, setting control flip flop, IC8A, back to normally high state. Timer IC5 is a power up clear circuit which empties the first in first out buffer memory and helps prevent random firing of the print solenoids during power up."

24

i

The

POLY 88 Microcomputer

System

If you are into computers or considering a system, the POLY 88 is the machine to contemplate.

HARDWARE

• Popular 8080 central processor • Single-board CPU

with ROM, RAM, vectored interrupt, real time clock,

single-step logic and serial I/O • Video interface card

generates video to TV monitor and provides parallel

keyboard input port • Serial and cassette mini-cards plug

directly into CPU with ribbon cables • Cassette

• ROM monitor with powerful debugger, video software,

bootstrap loader • Backplane and power supply on one

board simplifies construction • Rugged 6 amp power

supply • All circuit boards are high quality, double-sided

with plated-through holes • System is compatible with

a wide range of Altair peripherals • Minimum point to

point wiring means that the POLY 88 kit can go

together in three evenings!

ABOUT SOFTWARE

Software is the reason the POLY 88 was designed. The

operator can proceed from higher level languages like

BASIC to developing machine code with the aid of our

assembler. Our BASIC is a full 8K BASIC with character

and byte manipulation. Best of all, the programmer is

finally free of the teletype emulation mode so the video

display can be used to full advantage.

The video display provides a unique opportunity to write

new types of programs and games. Characters (16 lines

of 64) and graphics (48 by 128 grid) are part of the

processor's memory, so the display may be altered

rapidly — the entire screen written in less than 20

milliseconds.

POLY 88 hardware provides many

additional features that

programmers have come to expect,

such as vectored interrupt and real

time clock.

POLY-88

fie.

See it at your local computer store.

ARE YOU NEW TO COMPUTERS? The POLY 88 was designed for ease of use. No one should have to learn all the inner workings of computers just to enjoy one at a reasonable price. With the POLY 88, you can "play" pre-developed programs or explore the world of computer languages as your interests expand.

THE POLY 88 IS FOR EVERYONE Want to develop a new computer language? Want to fight Klingons? The POLY 88 provides a firm foundation upon which to build your interests and develop your skills.

POLY 88 SYSTEM PRICES:

SYSTEM 1 — Kit includes 8080 vectored interrupt

processor with real time clock, lA K of RAM and IK

monitor on ROM: Video Terminal Interface displays 16

lines of 32 characters on a video screen and has a

keyboard input port; cabinet, backplane, and power

supply; complete assembly, operation and theory

manual. $595.

SYSTEM 2 — System 1 plus 64 character line option and

Byte /biphase cassette interface kit. $690.

SYSTEM 3 — System 2 plus 8K of RAM with BASIC

and assembler programs on cassette tape. $990.

SYSTEM 4 — The complete kit. It includes system 3 and

TV monitor, keyboard and cassette recorder with all

necessary cables and connectors. $1350.

SYSTEM 7 — System 4 assembled, tested and ready to

run. $1750.

ACCESSORIES — 8K RAM kit, $300. Assembled $385 POLY I/O Ideaboard, hardware prototyping kit board. $55. Analog Interface (l channel) kit. $145.

Prices effective until January 15,1976. Prepaid orders shipped postpaid.

PolyMorphic Systems

737 S. Kellogg, Goleta, CA 93017 (805) 967-2351

wEm

xm.

tttfVHNi « *

mmz * *

mwmmdl 1J

mmn 9 %«

I

4£igg

3fe

Cassette Transports for the

"Roll Your Own" Hobbyist

William H Freeman 816 Meadow lark Ln Glenview IL 60025

Use of the Phillips Compact Cassette as a storage medium has been well established. Articles in BYTE and other publications have made the audio cassette just about the only storage device for the computer hobbyist. However, not enough attention has been given to the machine in which the cassette is operated. From various articles the usual transport mechanism is usually referred to as a cheapie or $30 cassette recorder. The usual control is a relay used to turn on the entire device. I regard this method as less than satisfactory and suggest that there are better ways.

When the low cost cassette machine is

Photo I: The A ml Ion A 9 cassette transport. It is similar to the A 7 transport varying only in a different head mount and the lack of an index counter on the A 7 model.

turned on or off with a relay, two difficulties are immediately apparent. First the pinch roller is always engaged, which can cause a dent in the roller if left too long in this position. The dent will cause serious wows in the tape speed. Second, the startup time will be excessively long. This leads to the conclusion that the entire tape transport mechanism should be controlled by the computer. All of the transport functions, play, stop, rewind and fast forward, should be available on command by the computer.

Audio cassette transports which will meet the requirement of being controlled by logic signals are available and can be purchased by the computer hobbyist. These transports have usually been available to the original equipment manufacturer (OEM), but the various manufacturers have indicated that they will sell to individuals or groups. One of the manufacturers of cassette transports, the Economy Company, has been actively promoting use of their deck for data storage, but more about it later.

To the best of my knowledge, there are only four companies in the US making and selling "bare bones" cassette transports. One of these companies, TELEX Communications, only has a manually operated transport, which cannot be controlled by a computer and is of no real interest to the computer hobbyist, even though it is a well constructed, rugged unit. The three remaining companies, Amilon Corporation, the Economy Company and the Mincom Division (Wollensak) of 3M, all have transports which are amenable to logic control since they have solenoids doing the work.

The Amilon Corp has two cassette transport models which might be used by the computer hobbyist. One model, the A9, is primarily an audio unit with mono or stereo heads for playing or recording usual audio type information. The other model, the A7, has characteristics slanted to the data storage business. The two machines are very much alike structurally, being built on the same basic frame. They are the same in size and weight, and require the same electrical inputs. Table 1 lists the performance details and shows the similarity of the two transports.

Optical end of tape sensing is available as

26

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PROGRAMMING LANGUAGES: History and Fundamentals

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The Computer Professionals' Book Club was organized for you, to provide an economical reading program that cannot fail to be of value. Administered by the McGraw-Hill Book Company, all books are chosen by qualified editors and consultants. Their understanding of the standards and values of the literature in your field guarantees the appropriateness of the selections.

How the Club operates: Every month you receive free of charge The Computer Professionals' Book Club Bulletin. This announces and describes the Club's featured book of the month as well as alternate selections available at special members' prices. If you want to examine the Club's feature of the month, you do nothing. If you prefer one of the alternate selections—or if you want no book at all—you notify the Club by returning the card enclosed with each Bu//et/n.

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P39185

an option. The lamp used is a 5 V, 100,000 hour rated lamp. Four kinds of cassette sensing options are available using up to four micro switches to sense the cassette in place, record tab A and tab B and side A. Side A sensing is detecting the off center slot on the back edge of the cassette which is present in a computer cassette.

Both the capstan and reel motors are AC induction motors which means long, reliable operation with no brush noise problems. The capstan motor is a synchronous one and is used to drive only the capstan, insuring accurate speed. The other motor is used to drive either the takeup spindle in the play, record, and fast forward modes or to drive the supply spindle in the rewind mode. Amilon claims this is the reason for the excellent wow and flutter performance as there is no motor acting as a drag when in the play or record mode. The mechanical structure is solid and stiff, assuring continued alignment of all parts. In particular, the pinch roller is mechanically isolated from the heads and is mounted on selfaligning instrument ball bearings to give even pressure on the capstan and minimizing any skew of the roller.

I was greatly impressed with the quality and attention to detail in this machine when the A9 model was demonstrated. Amilon Corp is also involved with digital cassette transports and some of their thinking has rubbed off on the audio cassette transport's design, to the audio transport's advantage. Photo 1 shows the Model A9 transport. The A7 model is almost identical, differing only in the head mount and its lack of an index counter.

You want to know what it costs? OK! Prices for the A7 transport, the data unit, start at $210 for one ($113.51 each in quantities of 100) which includes a precision head mount and a two track read and write head. End of tape sensing and cassette sensing switches are extra. Prices for the A9 transport start at $164.75 for one ($87.79 each in quantities of 100) which includes standard head mounts, stereo erase, and record and play heads. End of tape and cassette sensing switches are extra.

Next on the list of transports, alphabetically, is the Economy Company with its Phi-Deck. The Economy Co is a school book publisher for elementary education. Some years ago they added educational cassette

Table 1: Comparison of the A 7 and A9 cassette transports manufactured by Amilon comparing speed, accuracy} and power requirements of the two units.

Play or Record Speed

Speed Accuracy

Wow and Flutter

Reel Controlled Search Speed

A7

1.875 to 10.0 in per sec1" 4.763 to 25.4 cm per sec

±2% at any speed

not stated

50 in per sec average 127 cm per sec average

A9

1.875 or 3.75 in per sec* 4.763 or 9.53 cm per sec

±1% (±0.3% available) at any speed

<0.1% NAB weighted

not available

Fast Wind or Rewind

not available

70 sec for C60 cassette

Start Time

<40

ms

<300 ms

with speedup

circuit

<25

ms

Stop Time

<60

ms

<50 ms

Sensor Switches

SPDT

SPDT

Operating Humidity

0 to 95% noncondensing

Operating Temperature

+5° to+50°C

Storage Temperature

-20° to+70°C

Size

5.16 by 7.00 by 4.61 in

Weight

Capstan motor (synchronous)

Reel motor (fast mode)

(play mode)

Solenoids

*Ten different speeds available:

'Dual speed pulley available.

13.10by 17.78 by 11.71 cm

5.00 pounds 2.27 kilograms

117 V ± 10%, 50 or 60 Hz, 11 W

24 V ± 10%, 50 or 60 Hz, 13 W 18 V ± 10%, 50 or 60 Hz, 8W

24 VDC, ±5%, 600 mA

1.875, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 in per sec 4.763,5.1,7.6, 10.2, 12.7, 15.2, 17.8,20.3,22.86,25.4 cm per sec

28

scam

SOPTUI

Introducing SCELBAL, the new microcomputer language that's simpler than machine language.

ip^s

A complete language for "8008'7"8080" systems including source listings, routines, flow charts and more!

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Photo 2: The Phi-Deck Super Deck model manufactured by the Economy Company. This model allows varying tape speeds by varying the voltage to the capstan motor. The frame of the cassette transport is die cast, reducing alignment problems and making it quite rigid.

publishing to their product line. This produced demand for an audio unit to play the cassettes, with Phi-Deck the result. Over a year ago I saw the Phi-Deck demonstrated. Since that time the number of Phi-Deck models has increased to three; the advanced model is shown in photo 2. In addition to the transports themselves, the Economy Co is offering control boards to do all the tricky functions on command. The three models are referred to as fixed speed, variable speed, and Super Deck; their performance is tabulated in table 2. At least one personal computing manufacturer (Digital Group) is now offering Phi-Deck as part of a system product at quite reasonable prices.

As is usually the case, the performance figures in table 2 do not tell the whole story. All three transports have four DC motors. One motor drives just the capstan, the speed being maintained by a voltage regulator supplying current to the capstan drive motor. Another motor is used to drive the supply spindle. Still another is used to drive the takeup spindle. And the fourth motor actuates the yoke on which are mounted the heads and the pinch roller by means of a Geneva movement. (A Geneva movement translates rotary motion into linear motion. One revolution of the motor pulls the heads and pinch roller into position and another revolution moves them out of position. The motor always turns in the same direction!)

These DC motors are ideal for direct control with transistors since they run off

Table 2: Comparison of the three cassette transports manufactured by the Economy Company giving electrical comparisons and the physical dimensions and weight of the transports.

Speeds

Fixed

1.88 in per sec standard 2.00, 3.75, 4.00, 5.00, 6.00 in per sec optional

4.77 cm per sec standard 5,08,9.53, 10.16, 12.70, 1 5.24 cm per sec optional

Variable

0.40 to 20.00 in per sec 1.02 to 50.80 cm per sec

Super

1.00 to 10.00 in per sec standard

0.40 to 3.00, 0.60 to 5.50, 0.85 to 8.50

in per sec optional

2.54 to 25.40 cm per sec standard 1.02 to 7.62, 1.52 to 13.97, 2.16 to 21.59 cm per sec optional

Wow and Flutter

<0.25% at 1.88 in per sec 4.77 cm per sec

<0.25% at 1.88 in per sec 4.77 cm per sec

not stated

Bit to Bit Jitter

not stated

±2%

±2%

Speed Accuracy

not stated

±3%

±3%

Start Time

<100 ms

<100 ms

<100 ms

Stop Time

<100 ms

<100 ms

<100 ms

Forward and Rewind Time

<30 sec for C60 cassette

<30 sec for C60 cassette

<30 sec for C60 cassette

Power Required

+ 12 VDCat900mA

+ 12 VDCat^900mA

+18 VDC, -18 VDC, +11 VDC, +7 VD +5 VDC

C,

Size

2.60 by 5.40 by 6.30 in 6.60 by 13.72 by 16.00 cm

2.60 by 5.40 by 6.30 in 6.60 by 13.72 by 16.00 cm

3.00 by 5.50 by 6.20 in 7.62 by 13.97 by 15.75 cm

Weight

2.20 pounds

2.20 pounds

2.80 pounds

1.00 kilograms

1.00 kilograms

1.27 kilograms

30

12 V. A transistor in series with the motor acts as a switch controlled directly from the logic circuits. Very straightforward and simple. The logic and control circuits, which can be purchased or built, can do a lot of elegant performing on the part of the transport. In connection with end of tape and beginning of tape sensing options, one can cause the cassette to play to the end, then rewind to the beginning, stop or start playing all over again. By controlling the regulator supplying the capstan motor, different speeds of playing can be obtained. Cassette in place and record tab sensing are also options that are available. With the variable speed model, a different pulley is used for each speed range. The Super Deck model covers its entire speed range with only one pulley.

Of the three models, the one I recommend is the Super Deck as shown in photo 2. It has a diecast frame, making it quite rigid, reducing alignment maintenance problems. The other two models, the fixed speed and the variable speed, have a sheet metal frame that is somewhat flimsy and leaves something to be desired in ruggedness. Literature supplied by the Economy Co suggests that the Super Deck model was designed with data applications in mind, and as such, would be more attractive to the computer hobbyist.

The price of the fixed speed Phi-Deck, including a stereo head, is listed at $94.50 for one. The variable speed model, with all options, lists for $99.50, with either a two halftrack digital head or a regular audio stereo head. The Super Deck, with all control and sensing options, lists for $169 for just one at the time this was written. Electronic control board, remote control boxes and power supplies are also available.

Because of my past experience with maintenance problems, I have a prejudice against the use of DC motors. However, from data supplied by the Economy Co, it appears that they have made a very strong effort to improve the performance of their DC motors. Their data indicates that a mean time before failure of 5000 hours is a reasonable value. This would mean 2.5 years of operating time, assuming 40 hours a week for 50 weeks a year.

I have two objections to DC motors. First is the fact that the motors have brushes and commutators which wear, the brushes principally, and need to be replaced at intervals. In the case of the small motors being considered, many have no provision for replacing the brushes, so one must replace the whole motor. The second objection is that the brushes can cause noise in the associated circuitry, requiring additional

Photo 3: Woliensak Model 9576 and 9577 cassette transports. The two transports are identical, except the 9577 has an optical end of tape sensing unit The basic construction consists of two heavy metal plates separated by standoffs to form the frame. A flat panel supplied by the user is put on the top of the transport to protect the inner mechanisms.

Play and Record Speed

Speed Accuracy

Wow and Flutter

Rewind and Fast Forward Times

Solenoids

Light Source {Model 9577)

Sensor (Model 9577)

Size

Motor Power

Model 9576 and 9577

1.875 in per sec 4.763 cm per sec

±2%

<0.25%

45 sec for C60 cassette

24 VDC 72 ohms

subminiature lamp 5.0 VDC @ 0.075 A

2N5778 Photodarlington

5.63 by 6.75 by 4.78 in 14.29 by 17.15 by 12.14 cm

117 V, 50 or 60 Hz, 10 W

parts to suppress it. AC induction motors

have no brushes, hence no noise or wear problems. With oilite sleeve bearings they run quietly for a long, long time.

The last transport models to be described are made by the Mincom Division of the 3M Company. There are three versions, very much alike: Model 9575, Model 9576 and Model 9577. Model 9575 is a manually controlled mechanism and is of no interest to us. Models 9576 and 9577 are solenoid controlled mechanisms which are what we want. All models have the same basic drive

Table 3: Performance characteristics of the cassette transports manufactured by Woliensak. The two models are the same except that the 9577 has an optical end of tape sensing unit that the 9576 does not have.

31

Mean Time

Price

Performance

Before Failure

AMILON

high

excellent

very good

PHI-DECK

medium

very good

very good

WOLLENSAK

medium

very good

excellent

Table 4; The author's comparison of the best tape transports manufactured by Am/Ion, Economy Company, and Wollensak. The ratings are in relation to how well the objectives of low price, high performance, and a long mean time before failure, are achieved.

arrangement. An AC induction motor, shaded pole, drives a large flywheel through a rubber tired idler. The flywheel is on the capstan shaft. The supply and takeup spindles are driven from the flywheel with rubber tired idlers. No belts are used in the drive mechanism. There is one belt but it is used to run the index counter. In the two models of interest, three solenoids control the operating functions. One solenoid is pulled up for play or record; another is pulled up for fast forward; and a third for rewind.

The Mode! 9576 and Model 9577 are identical in all respects except that the Model 9577 has an optical sensing circuit included. This optical sensing consists of a small 5 V lamp and a phototransistor. This will provide end of tape and beginning of tape sensing. Table 3 lists the performance of both models.

Photo 3 shows the basic construction of the Wollensak transport, consisting of two heavy plates separated by standoffs forming the frame. The user must supply some kind of flat panel with cutouts for the cassette tray, the eject lever and the index counter. Four screws will attach the unit to this panel. This transport, like its big brother units made by Wollensak, is well built and should have a long service life with a minimum of maintenance. My experience with the full size Wollensak cassette units is that they run, and run, and run.

The latest prices available to me are $79.50 for Model 9576 and $85.75 for Model 9577 in quantities of 1-9. In 100 lot quantities prices are $65 and $71.25, respectively. Heads for the transport are extra.

How should these three cassette transports be evaluated? We can use three criteria: price, performance and reliability. Price is easy, just look at the figures. Performance and reliability are not so easy to establish because each potential user will assign different values to the various details of performance depending on the end objective and his or her bias. My bias has already been stated. My evaluations are given in table 4.

Some explanation may be necessary. Amilon is rated excellent in performance because of its very low wow and flutter

figure and its tight speed control with a synchronous motor. Wollensak is rated excellent in the mean time before failure column because of my past experience with Wollensak cassette units covering more than six years of usage in the school environment.

If I had an overflowing purse, I would buy the Amilon unit because of its excellent performance. Price is, however, a very demanding factor, so the Wollensak is my choice as the best buy. The Phi-Deck comes in very close in this decision. It is a certainty that not all readers will agree with this evaluation, which is certainly your privilege. The individual who is putting out the green stuff is entitled to make his or her own choice based on what is felt to be important. As they say, "That's what makes a horse race."

Where can you get one of these cassette transports? In alphabetical order: for an Amilon deck write to Leonard Rosenblatt, Amilon Corp, 49-12 30th Av, Woodside NY 11377; for a Phi-Deck you can find the address in ads in BYTE, but here it is anyway — The Economy Co, Triple I Division, 1901 N Walnut, Oklahoma City OK 73105; and for the Wollensak deck, write to Scott Goff, Sales Manager, Wollensak OEM Products, Mincom Division, 3M Co, 3M Center, St Paul MN 55101.

As a kind of post script to this article, I have included a few words of wisdom about using cassette transports, or any tape machine. Preventive maintenance will keep your cassette transport running without problems. Regularly do the following:

1. Clean the capstan, pinch roller, heads and guides after every 10 hours of operation. Use a good fluorocarbon, low toxicity head cleaner; one that will not attack rubber or plastic parts.

2. Keep all parts as dust free as possible. Use a dust cover over the transport when not in use.

3. Lubricate as often as the manufacturer specifies. Do not overlubricate; be sparing with the oil.

4. Demagnetize the heads, capstan and guides with a good head demagnetizer after every 10 hours of operation.

Overall performance will be considerably affected by the quality of the cassette used. Use a good to high quality cassette. Cheap cassettes will have poor tape quality and, even worse, poor mechanical performance which will adversely affect the tape speed. You will find that with the better to best tapes, you get better recordings with better frequency response and all around better performance."

32

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OHIO SCIENTIFIC INSTRUMENTS

Dept. B 11679 HAYDEN STREET, HIRAM, OH 44234

(216) 569-7945

Continued from page 10

at the servo and in the displays used to monitor the position count.

The program is quite simpie: it generates a positive going pulse on the bit 0 tine of the Pi A output port, a puise which lasts from J ms in length to 1 + 0.012 n ms where n is

an 8 bit number which is incremented once each time around the outer loop of the program. The 0.012 ms factor is based on the processor's clock at the time of the test, 500 kHz, and the 6 state loop at addresses 201F and 2020 which times the width of the variable portion of the pulse. With the servo illustrated in photo 1} the wiring used was as

PEN AT LOCATION (X,Y)

COLOR KEY

MOVABLE SERVO ARM AND

ITS ARC RANGE WITH FIXED SERVO POSITION SHOWN.

FIXED SERVO ARM AND ITS

ARC RANGE.

ENVELOPE OF TYPICAL

MOVABLE SERVO POSITIONS

Figure 2: This diagram shows the concept of how to build a plotting bed based upon two model aircraft servo mechanisms. The method of building consists of fixing one servo to the plotting bed, with a lever arm of length R. At the end of that lever arm, fix the second servo with a second lever arm of length R also. The end of the second arm should have a pen affixed to a solenoid mechanism or other actuator, allowing the pen to be raised or lowered. Due to weight considerations, the second servo should be

mounted so that it slides on a teflon skid or rolls on some form of loose ball roller. The mathematics of calculating X and Y given angles 0 and 6 is shown in the drawing. To invert the calculation requires use of a reiterating calculation to a set of <j> and 6 values which solves the desired X and Y position. To use this plotter requires a system which has sufficient memory to run a fixed point trigonometric package with at least 16 bits of precision, assuming a 13 bit precision for the angular parameters of the servos.

34

follows; +5 V was the red wire, ground was the black wire, and the TTL output of PI A bit zero was used to drive the blue wire.

The results of the test are somewhat interesting. When this program was run, the servo was observed to have a total travel of 180° rotationaliy. A unique relationship between the integer pulse width parameter stored in DATA in this program and the shaft position was observed, but the minimum acceptable pulse width for the device we purchased was probably 1.3 ms. The reason for this conclusion is that the servo illustrated two regimes of settings: For counts of 00 to 19 hexadecimal (0 to 25 decimal) it swept out clockwise motion from 180° to 0° (relative angles). The motion was partitioned into very noticeable and large steps over this range. Then, from counts 19 to D6 the servo swept counterclockwise from 180° to 0° with what looked like roughly linear steps. This range of 189 steps is about 0.95° per step. At the high end of the count range, D9, the servo hit its limit stop. Thus, based on this experiment, the actual numbers work out as follows:

Minimum pulse width: 1 +0.012X25= 1.3 ms

Maximum pulse width: 1 +0.012 X 214 = 3.6 ms

In using this servo, or any similar mechanism for an experimental project, readers would want to investigate the linearity of the position output with respect to the control parameter, and use a higher resolution timing method. For example, to make the world's least expensive plotter, using a 13 bit counter with a 2 MHz crystal clock, decimal counts of from 2600 to 7200 would cover the range of timing values found above, giving a control parameter range of 0 to 4600, approximately 0.04° per step assuming linear characteristics. Using trigonometry, this corresponds to an arc motion of 0.00683 inches per step at the end of a 10 inch lever arm (0.17 mm per step at the end of a 25 cm lever arm). Using two such servos, and working out the trigonometry of two connected lever arms, one on a servo fixed to the plane and one on a servo at the end of the fixed servo's lever arm, it should be possible to homebrew an XY plotter for less than $100 by just buying two such model aircraft servos. Since I have no engineering specs yet on these devices, I can't say how accurate the plotter would be, but it would certainly drawl See figure 2. ■

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35

A 6502 Op Code Table

Lemuel A Fugitt 11316 Linares St San Diego CA 92129

Table 1: An explanation of the abbreviations used in the 6502 reference chart.

LEAST

SIGNIFICANT 4 BITS

abs: abx: ace: aby: i,x:

imm:

imp:

ind:

rel:

zer:

zpx:

zpy:

absolute.

indexed absolute using x register,

accumulator.

indexed absolute using y register.

indexed indirect using x register.

indexed indirect using y register.

immediate.

implied.

absolute indirect.

relative.

zero page.

indexed zero page using x register.

indexed zero page using y register.

not implemented.

MOST SIGNIFICANT 4 BITS

Here's a nice compact reference chart to help you debug those hexadecimal dumps from your 6502 microprocessor. To use the table, find the most significant digit along the top of the chart and follow the column down until you reach the value of the least significant bit of the hexadecimal code on the horizontal row. You now have not only the mnemonic but also the addressing mode being used. Table I is an explanation of the abbreviations used in the chart. ■

\

\ .

1

2

3

4

5

6

7

8

9

A

B

C

D

E

F

0

BRK

imp

BPL

rel

JSR

abs

BMI

rel

RTI imp

BVC

rel

RTS imp

BVS

rel

*

BCC

rel

LDY imm

BCS

rel

CPY

i m m

BNE rel

CPX

imm

BEQ rel

1

ORA

ORA

AND

AND

EOR

EOR

ADC

ADC

i,y

STA

STA

LDA

LDA

CMP

l,X

CMP

i,y

SBC

i,x

SBC

2

*

*

*

*

*

*

*

*

*

*

LDX

*

*

*

3

*

*

*

*

*

*

*

♦

*

*

*

*

*

*

*

»

4

*

BIT zer

'

STY

zer

STY

zpx

LDY

LDY

zpx

CPY

zer

CPX

zei

5

ORA

zer

ORA

zpx

AND zer

AND zpx

EOR

zer

EOR

zpx

ADC zer

ADC zpx

STA

zer

STA zpx

LDA zer

LDA

CMP zer

CMP zpx

SBC

zer

SBC zpx

6

ASL

zer

ASL zpx

ROL

zer

ROL

zpx

LSR

zer

LSR zpx

*

*

STX

zei

STX zpy

LDX

zer

LDX

zpy

DEC

zer

DEC

zpx

INC zer

INC

zpx

7

*

*

*

*

*

*

*

*

*

*

*

*

#

*

*

8

PHP

imp

CLC

imp

PLP

i m p

SEC

imp

PHA

imp

CLI

imp

PL A

imp

SEI

imp

DEY imp

TYA

imp

TAY

imp

CLV imp

INY

imp

CLD imp

INX imp

SED

imp

9

ORA

i m m

ORA

aby

AND

imm

AND

aby

EOR imm

EOR

aby

ADC

imm

ADC aby

*

STA aby

LDA

i m m

LDA aby

CMP imm

CMP aby

SBC imm

SBC

aby

A

ASL ace

*

ROL

LSR

*

*

*

TXA imp

TXS imp

TAX imp

TSX

imp

DEX

imp

*

NOP i m p

B

*

*

*

*

*

*

*

*

*

*

#

C

*

*

BIT abs

*

JMP

*

JMP ind

•

STY abs

LDY abs

LDY abx

CPY

abs

*

CPX

abs

*

D

ORA

abs

ORA abx

AND

abs

AND a b x

EOR abs

EOR

abx

ADC abs

ADC

abx

STA abs

STA

a b x

LDA aba

LDA abx

CMP

abs

CMP abx

SBC abs

SBC abx

E

ASL abs

ASL

a i) x

ROL abs

ROL

LSR abs

LSR

*

STX

abs

LDX

abs

LDX aby

DEC abs

DEC a b x

INC abs

INC

abx

F

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

36

DIGITAL DATA RECORDERS

USING 3M DATA CARTRIDGES

Model 3M3 $199.95

BRAND NEW DESIGN

Featuring the radically new "UNIBOARD" method of construction for data cartridge drives. The major computer manufacturers are changing from cassettes to cartridges at a rapid pace because of freedom from binding and greater data reliability. Now, these professional type units are priced within the range of all data users. Being made primarily as OEM data storage units for the world's major manufacturers, these units, together with controller board and software ROM, are being made available to the individual user as well.

* Appearance and specifications may be changed slightly following acceptance tests now being conducted by OEM users.

Model 3M1 $169.95

MODEL 3M3 - Uses the 3M Data Cartridge, model DC300. This cartridge contains 300 feet of .250 tape in a sealed container. Records and plays at 9600 baud NRZ, 4800 baud P.E. Nominal speed 8" per second. Max. recommended flux density 1200 fcpi. Using four tracks, you can store nearly 2 megabytes of data on a cartridge. Cartridge measures 4" by 6". Turns counter indicates tape position. Inter-record gap light gives more accurate position. 2SI0(R) is not required for use, but is highly recommended for 8080 and Z80 systems.

COMMON SPECIFICATIONS: FULL SOFTWARE CONTROL of record, play, fast forward and rewind. LED indicates inter-record gaps. EOT and BOT are sensed and automatically shut down recorder. Can also be manually operated using the switches on top which parallel the software control signals when not under software control. Signal feedback makes it possible to software search for inter-record gaps at high speed. 117V - 60 Hz - 5 watts.

TWO I/O PORT CONTROLLER WITH ROM - Controls your terminal and one or two cassettes or cartridge units. On board ROM (For 8080 and Z80) has terminal and cassette software for turn on and go operation. NO MORE BOOTSTRAPPING. Plug in compatible with Altair and IMSAI. Loads and Dumps memory in Hex from the keyboard, formats tape files, punches tape, functions as a word processor and searches for files and four letter strings within files. Keyboard controls the cartridge units above on rewind and fast forward. Special keyboard codes enable you to dump and read Phase Encoded tapes as well as NRZ tapes. (Including K.C. Std.) Call routines give access to these from your software.

MODEL 2SI0JR) -With 1 ROM for NRZ Cassettes $169.95

(Assembled & Tested) (Half of above Program)

With 2 ROM's for Data Cartridges and

P.E. cassettes. $189.95 (Full Program)

Kits available for $30 off above prices.

OVERSEAS: EXPORT VERSION - 220 V - 50 Hz. Write Factory or— Megatron KG, 8011 Putzbrunn, Munchen, W. Germany; Nippon Automation 5-16-7 Shiba, Minato-Ku, Tokyo; EBASA, Enrique Barges, 17 Barcelona, Spain; Hobby Data, SpireaVagen 5, Malmo, Sweden; G.Ashbee, 172 Ifield Road, London SW 10-9AG.

MODEL 3M1 - Uses the 3M Data Cartridge type DC100A. This cartridge contains 150 feet of .150 tape and is the same cartridge used by H.P. and others. Runs at 4800 baud NRZ, 2400 baud P.E. Tape speed adjustable, but nominally set at 5"/second. Maximum recommended flux density 1200 fcpi. Cartridge measures 2-1/8" by 3-1/4". This model is ultra compact, yet extremely capable. It is intended for word processing, mailing list use and other applications requiring the compact storage of data. Data location is by inter-record gaps and automatic file search. See Common Specs and 2SIO(R) below. 2SI0(R) is not required for use, but is highly recommended for 8080 and Z80 users.

For 8080 and Z80 users: Comes complete with software program listings for the programs on the 2SI0(R) ROM below. 6800 software is being written, but not yet completed. These programs give FULL SOFTWARE CONTROL.

CARTRIDGE AVAILABILITY: Cartridges are made by 3Mr ITC, Wabash and others. They are available at all computer supply houses and most major computer service centers. We can also supply them at normal current list prices.

NEW: AUDIO CASSETTE INTERFACE* Phase Encoding interface for use with audio cassettes or NRZ recorders. Runs 2400 baud phase encoded on good quality audio cassette recorders. May also be used with 2SI0(R) above to use the 2SI0(R) cassette programs with your audio cassette player. Can also accommodate "Tarbell" tapes and K.C. Std. tapes.

$50.00, Wired & Tested. - $35.00, Kit Form.

* NOTE: You do not require an interface with the 3M1 and 3M3 unless you Phase Encode. But, you do need an interface to use the 2SI0(R) with your own audio cassette.

"COMPUTER AID" and "UNIBOARD" are trademarks of the NATIONAL MULTIPLEX CORPORATION. The 3M Data Cartridges are covered by 3M Patents and Marks. "UNIBOARD" Patents Pending.

For U.P.S. delivery, add $3.00 each item. Overseas and air shipments charges collect. N.J. Residents add 5% Sales Tax. WRITE or CALL for further information. Phone Orders on Master Charge and BankAmericard accepted.

NATIONAL MULTIPLEX CORPORATION

3474 Rand Avenue, South Plainfield, NJ. 07080, Box 288 Phone (201) 561-3600 TWX 710-997-9530

The Digital Cassette

0 0 1 I 0 I 0 I

Jack Breimeir

The Economy Co

1901 N Walnut

POB 25308

Oklahoma City OK 73125

Ira Rampil

917 Engineering Research Bldg University of Wisconsin Madison Wl 53706

We've now seen an illustration of the techniques involved in the recording and playback of binary strings on magnetic tape (in part one last month). These techniques are all that would be required if the cassette tape transport mechanism had instantaneous start and stop, and perfect speed regulation. The read and write electronics would need to have very wide bandwidth, as shall be seen later, and the tape itself would have to be absolutely error free. Since there are problems in meeting each of these requirements, a great deal of effort has gone into data code conversion schemes that tend to alleviate the problems. Many different codes have been developed, but only a few have found widespread application and usage. The number of codes in use, in fact, is likely to decrease in coming years, as there are strong incentives in the industry to settle on standard coding schemes which would then be used by everyone. There is no urgent reason, however, for amateurs to embrace the industrial standard, especially if there is no intent to exchange tapes using the medium.

There are several specific qualities to examine when selecting a coding scheme. Dr A E Whitehouse of the Dept of Computer Science, University of Manchester, in his doctoral thesis, selected the following seven characteristics inherent in each scheme to which relative ratings can be assigned. These criteria are the column headings of table 1, which compares a number of coding schemes.

1. Bandwidth: The range of frequencies required to be passed by the read or write amplifiers for a given rate of data throughout should be minimal. Most importantly, low frequency response requirements should be avoided because

a) low frequencies contain much noise like rumble, wow and flutter, and

TRACK A

TRACK B

TRACK A

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TRACK B

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38

Subsystem:

Part 2,

Digital Data Formats and System Considerations

b) difficulties in design of the read electronics. In general, the narrower the signal bandwidth, the better the signal to noise ratio. [Compare NRZ (nonreturn to zero) and PE (phase encoding) methods of en* coding as seen in figure 1.]

2. Circuit Complexity: The cost of any system is proportional to its complexity. However, as can be seen in table 1, there are many performance trade-offs that improve with increasing complexity.

3. Efficiency: The efficiency of a code is a measure of data density produced by it. Efficiency: = 100 -r (flux changes per bit)

4. Inter Symbol Correlation: For the best performance, the codes used to represent binary ones and zeros should be as different from each other as possible. One hundred percent correlation occurs when the symbols used for ones and zeros are equal and opposite.

5. Noise: A qualitative measure of sensitivity to tape noises such as drop outs.

6. Read Resolution: The percentage of time in each bit that is allowed in order to decide whether it is a one or a zero.

7. Self Clocking: Does this code inherently provide its own bit rate clock for data reconstruction? If not, an external clock must be provided and

Table 1: Comparison of magnetic media encoding formats. This is an overall chart of several different characteristics; several of the methods are discussed in more detail in the text. In the waveform samples, the vertical lines mark data bit times, and the horizontal reference line separates north from south magnetization (or vice versa).

Code Name

Number

of

Data

Tracks

Sample Waveforms

Signal Bandwidth

Circuit Complexity

Storage Efficiency

Intersymbol Correlation

Noise Immunity

Resolution

Is It

Self

Clocking

Transport

Speed Limitations

Applications and Comments

Return to zero (RZ, RZ pulse)

1

-A

wide

simple

50%

50%

poor

poor

no

strict

Of historical interest, not self erasing

Bipolar RZ

1

-B

medium

moderate

50%

100%

poor

poor

yes

lenient

Of historical interest only

Return to bias (RB)

1

-C

wide

simple

50%

100%

poor

poor

no

strict

Of historical interest only

Non return to zero

(NRZ,NRZ1, NREC)

1

-D

wide

simple

100%

100%

fair

1 00%

no

strict

Used on older 7 and 9 track commercial magnetic tape drives

NRZ-mark (NRZM, IMRZ1)

1

-E

wide

simple

100%

75%

fair

1 00%

no

strict

Used on contemporary commercial tape drives

Complimentary NRZ (CNRZ)

2

-F

wide

simple

50%

fair

fair

100%

yes

very lenient*

Incremental recorders and data loggers, calculator strip recorders.

Complimentary RB (CRB, 4 phase)

2

-G

wide

simple

25%

50%

good

good

yes

very lenient*

Off line terminals; uses much tape due to low efficiency

Pulse ratio recording (PR,PW, SRT)

1

-H

medium

moderate

33%

good

good

>=5Q%

yes

tolerant of slow drifts

Useful on hub driven tape drives (eg: Redactron)

Phase Encoding (PE, split phase, Manchester 11 + 180)

1

-1

narrow

complete

50%

100%

good

75%

yes

tolerant of fast and slow change

Currently the industry standard for all tape systems, commonly used for floppy disks.

Manchester I (also PE)

1

-J

narrow

complex

50%

100%

good

75%

yes

tolerant of fast and slow change

Same as above.

Note: Two channel recording methods are lenient with respect to speed variations, but have tight head skew requirements which do not exist for single channel recording methods.

39

NON RETURN TO ZERO

\

..PHASE ENCODED (PE)

AMPLITUDE (POWER)

<t>)

GOOD SIGNAL TO NOISE RATIO

NRZ: PE:

TYPICAL DATA WAVEFORMS

0

0

r-i

—\ 1 1 111

0

0

1 0 1 1 0 0 0 1 0

Figure 1: Frequency spectrum requirements for a practical system depend upon the nature of the encoding and the noise characteristics. At (a), two common encoding methods, non return to zero (NRZ) and phase encoded (PE) data are shown as a spectrum of ampiitude versus frequency. NRZ reguires a flat response virtually from zero frequency up to the data rate. PE requires a frequency hand response characteristic of one octave in the vicinity of the data rate. Looking only at the signal, and knowing electronic design rules of thumb such as the one that it is easier to make a narrow band amplifier than a wide band one, PE looks like a better method. Then, adding in a system noise characteristic as at (b)} it becomes obvious that PE or any system with limited bandwidth is to be preferred over NRZ. NRZ is the simple method to generate (it is just a time ordered stream of data bit values), but its signal to noise ratio runs into problems due to noise at the low frequencies.

since it is asynchronous to the data, this code cannot be used reliably at high data rates. For additional information beyond Whitehouse's criteria, two extra columns have been added to table I.

8. Tape Transport Limitations: What requirements does this particular code place on tape speed accuracy and stability?

9. Usual Application: These various coding schemes present different trade-off balances, and therefore have found themselves in a wide variety of different applications. A typical application is presented for each code.

To efficiently analyze the entries in the table, it is possible to divide them into two groups. The division concerns the number of tracks required to write or recover data. Some codes require two channels of recording to recover one channel of data. These codes are, for the most part, older and space inefficient techniques. The advantage in using them is that the coding circuitry is relatively simple and these codes tend to be very speed tolerant. For the amateur, however, the cost reduction in logic is more than offset by the additional cost of a two track tape head, an extra signal processing channel, and the problem of intertrack head misalignment or head skew as illustrated in figure 2. Therefore, with the advent of quality low cost tape transports and speed tolerant one track codes, it is wisest to stick with single track recording. There is an exception called "mark track" recording which will be discussed later. There are four techniques which have found application among amateur applications.

Non Return to Zero (NRZ)

Conventional NRZ consists of recording a constant saturated level for the duration of the bit. For example, a string of ones input to the cassette will be recorded as a constant north magnetic level which will persist until a zero occurs in the input string. Obviously the efficiency is high; there is a maximum of one transition per bit, usually less. The possibility of long strings of either zeros or ones requires that the signal processing chain have a very wide bandwidth, extending down to near zero frequency. Another problem with this system is that it is not self clocking, therefore an asynchronous receiver such as a UART must be used to convert the output of the tape back to synchronized parallel bytes. Assuming a very stable tape speed, both in the long term and short term, this technique is limited by tape noise, the magnetic data transfer head, and the limiting speed of the UART. There is a way of improving the reliability of asynchronous NRZ by making it synchronous: Recording a separate clock track at the data rate while simultaneously recording data in another channel provides a means of synchronously gating the data at playback, thus eliminating the need for a UART (assuming skew is not a problem). The National Multiplex Co of South Plainfield NJ provides amateur digital cassette recorders using NRZ or clocked NRZ'at up to 2400 bits per second; they also sell NRZ electronics boards that can be planted in an ordinary audio tape recorder. This product is capable of up to 4800 bits per second, depending on tape speed.

40

Complimentary Return to Bias (CRB)

Complimentary return to bias is a two track technique which resembles the RB code. In RB each data cell has a binary state, north or south, and so in two track CRB each data cell is set to one of four states:

1. Both tracks at south

2. Track A at south, track B at north

3. Track A at north, track B at south

4. Both tracks at north

State 1 represents a "no data*' condition as in an inter record gap. States 2 and 3 respectively represent zero and one. State 4 is a framing signal which can be used to represent conditions like end of block or end of byte. This code is both noise and speed tolerant. Its clock signal can be derived from a simple OR of both tracks, since except in state 1, there are transitions every bit. This code, however, has poor utilization of available tape. In other words, it is a low density technique and the bandwidth is even wider than for NRZ. As a two track technique it is subject to skew problems. The circuitry to implement CRB is a fairly simple logic network.

Pulse Ratio Recording (PR)

In the pulse ratio coding method each data cell uses two flux transitions in three possible locations. The first flux transition of each cell is a positive transition, from south to north. Its presence defines the beginning of the data cell and gates a clock on. The contents of the data cell, ie: the bit, is determined by the percentage of time spent at north as compared to south, within each data cell. There is a very simple method to decode PR by the use of a bidirectional counter in hardware or software. The previously mentioned positive flux transition starts the counter going up. The next flux transition is of course a negative one. Its arrival switches the mode of the counter into down counting. The transition after that is the clock pulse for the next cell; it resets the counter and clocks out the contents of a flip flop which records the possible transition of the BORROW output of the counter - then the process starts over. It is the borrow signal which contains the data in the cell. If for a one bit, as in table 1, the north time was greater than the south time, then the counter result is a positive number; no borrow was required and the flip flop holds a one, the contents of the cell. A zero on tape has a longer south time than north time: The counter going into underflow drops the BORROW to zero for one clock cycle. The flip flop records the drop and holds a zero. This method provides excellent

resistance to long term speed variations, provided the counter has enough precision. The bit-to-bit jitter resistance, however, is not so good due to the less than 50% read resolution. This resistance and resolution can be improved by accentuating the pulse width difference; but then noise immunity suffers because the bandwidth goes up. This technique's primary advantage is that the circuitry is the simplest for a one track self clocking code.

Phase Encoding (PE)

Phase encoding has been selected by all of the relevant standards organizations as the way to go. Most commercial manufacturers provide a PE option for their cassette decks sold to original equipment manufacturers (OEMs). The most widely used form of PE, also known as "split phase" or "Manchester II +180" is a single track, self clocking technique. The definition of the code places two landmarks in each data cell. The landmarks are actually times during a data cell when transitions are made in the tape magnetization level. The data is actually stored in the direction of the magnetic transition at the midpoint of the cell. This transition occurs at "data time" and is specified as south to north for a one, and north to south for a zero. In order to assure that the magnetic signal will be at the right

HEAD ALIGNMENT PROBLEMS

BUSINESS END OF A TAPE HEAD

-GAP SKEW CAUSED BY LIMITATIONS IN MANUFACTURING ACCURACY

GAP SKEW CAUSED BY TILTEO HEAD MOUNTING

Figure 2; Head alignment and manufacturing tolerances cause a phenomenon called gap skew in muititrack heads. At (a), the tolerances in manufacturing of the head itself cause one component of skew. At (b), a second source of skew is due to the fact that the head may not be perfectly mounted relative to the tape. The tilt causes a skew between otherwise perfectly manufactured gaps. The actual skew measured is a combination of both effects. The picture is exaggerated, but a small misalignment of, for example, 0.005 inch (0.13 mm) means a difference of 200 ms in the relative timing of two tracks being read at 25 inches per second (64 cm per second). A typical manual for a tape drive unit will warn the controller builder to put in circuitry to compensate for intertrack skew totalling several bits if parallel data is used. This skew problem argues strongly in favor of single track recording techniques.

41

Sample Circuitry for Several Different Coding Techniques

This circuitry assumes that the tape deck write head is driven directly for output, and that tape input signal processing electronics produces the +

and — flux transition clocks (low going 1 f~)

as output. Encoding consists of preparing the proper signal to drive the write head from NRZ data, and decoding consists of converting the flux transition information back into NRZ data, possibly along with clock information derived from the tape.

a) NRZ coding. The output NRZ data simply drives the head directly. A UART or other asynchronous data format must be used for the parallel to serial conversion, and clock references used in writing are assumed to be

valid within a few percent when reading the data back, hence the tight tolerances on speed. Decoding of the flux transition clocks is done simply by driving an RS flip flop.

b) NRZ1 coding. The output NRZ data is converted to NRZ1 by using it to gate the clock driving a toggle flip flop (here a JK flip flop set up to toggle). The input flux transition data is converted back to NRZ by using the logical OR of the two transition clocks to drive a retriggerable oneshot with period (R and C) set up equal to the bit period. The fixed width of this oneshot also makes this method highly speed dependent.

c) PE coding. The output PE data is generated

polarity for the next data time, an additional transition can occur if needed at "phase time." Phase time occurs at the beginning of each data cell. The phase transition occurs at phase time only if the preceding bit is the same as the bit to be written. The phase bit is ignored by the read circuitry except for clocking purposes. In the inevitable comparison of phase encoding with non return to zero, it first appears as though non return to zero provides high bit density per unit length of tape. True, phase encoding is less space efficient than non return to zero, requiring the time budget of two flux transitions per data bit compared to one flux change per bit. There are, however, extenuating circumstances which throw the balance in favor of phase encoding. The advantages come from phase encoding's requirement that each data cell have at least one flux change and not more than two. Thus the bandwidth needed for a phase encoded signal processing chain extends only one octave, from the data rate to twice the data rate. The bandwidth for non return to zero electronics extends from zero up to the data rate, possibly 5 to 10 octaves. The wide range of flux change frequencies also wreaks havoc on peak shift and amplitude fluctuation phenomena due to the tape itself. As we saw previously, peak shift and amplitude fluctuation cause problems in the recovery of raw bit strings from the tape. These phenomena are well defined in phase encoding: Their effects are small and easily compensated. Self clocking is another side benefit of having at least one transition per bit. A very simple form of self clocking derived from phase encoding is a monostable set to the data rate. Triggered by each data transition, its output provides clock gating for each previous data bit. More sophisticated techniques which have great tolerance for tape speed variation and noise involve

tracking oscillators or phase locked loops. Such systems will compensate for missing pulses by providing clock pulses of their own if the tape messes up momentarily. Phase encoding requires that the first byte written in each block be a preamble word consisting of 8 data transitions like the byte 01010101. The preamble allows time for the phase locked loop to get into lock step with the data rate. Block diagrams for various forms of data encoding and recovery will be illustrated later.

Since they have now appeared on the personal computing market, a few words are in order concerning GCR, Group Coded Recording. GCR is different from the previously discussed codes in that here code bits do not bear a one to one correspondence to their input bits. Instead, a code converter ROM, like an ASCII to EBCDIC converter, transforms each parallel input group into a slightly longer output group which is then put on the tape. Playback involves the opposite process. This type of coding was originally developed for ultra high performance nine track drives and combines the best features of phase encoding and non return to zero. The circuitry, however, is very complex.

Error Detection

There is no easy and cheap method for self correcting data errors that occur on tape read operations. There are redundant data techniques which would work but at a great sacrifice in data throughput. On the other hand, there are several ways of detecting errors. This is almost as good as correcting the errors, since about 9 out of 10 errors are soft errors; that is to say they disappear upon retrying the read. Only about 1 in 10? to 109 bits read result in a hard, or permanent, error. There are also two very

42

from NR2 data using a clock at twice the data rate, and the NRZ data itself. Two methods are shown here, one which can be built from gates, and a second using an RCA CD4037A integrated circuit. The input de

coding methods can range from the simple oneshot method shown here to complicated phase lock loops which are much more error resistant. For the oneshot version, AT should be set to be 1.5 bit cells.

M

HEAD DRIVER

NRZ C>—

FROM

CONTROLLER

>

V

RS FLIP FLOP + FLUXG

OUTPUT NRZ ENCODE

TX

r-v> NRZ TO

1-^ CONTROLLER

INPUT NRZ DECODE

(b)

NRZ „

fromO

+ 5V A

CONTROLLER

DATA

clockO—

FROM CONTROLLER

X>

CK K

HEAD DRIVER

->

OUTPUT NRZ I ENCODE

WRITE

HEAD

v Di

IT O

-FLUX

£

H

C

+5V R

+ FLUX | C 1

RETRI6GERABLE ONE SHOT

INPUT NRZ I DECODE

(Cj

+ 5V .„ a -2

CLOCK

AT 2XO

DATA RATE FROM CONTROLLER

NRZ

DATA _^ FROM n>

CONTROLLER

EG:7473l

CK D EG: 7474

ONE BIT SHIFT REGISTER OLD DATA

PHASE ENCODE (RANDOM LOGIC)

CLOCK^ AT 2X\Z>

DATA RATE

FROM CONTROLLER

NRZ DATA

FROM O

CONTROLLER

tj>«

CD4037A

PHASE ENCODE (RCA CD 4037A LSI LOGIC)

+ FLUX TTO

FROM READ ELECTRONICS

-FLUX

if o

t-5V

AT

C,

'%-*>Zl 'N H[B IT

COMBINE

I

AT =

1.5

DATA RATE

DERIVED CLOCK •O SYNCHRONOUS WITH DATA

NRZ TO CONTROLLER

GATE RETRIGGERABLE, ONE SHOT

i>

:=L>

1 r RS F

-ONRZ DATA

TO CONTROLLER

LIP FLOP

INPUT PHASE ENCODED DATA DECODER (USING RETRIGGERABLE ONE SHOT)

43

-100001 R 0001011000000110

IIOOOOOOOOOOOOIOI

(CR-16 POLYNOMIAL) 17 BITS LONG

II no IOOOM

{DATA BLOCK) n BITS LONG

(CRCC) 16 BITS

Figure 3: A hypothetical cyclic redundancy check polynomial division, in a CRC calculation, the data is divided by a 17 bit cyclic redundancy polynomial to yield a result and a 16 bit remainder term, it is the remainder term which is used as the check word for error detection. The beauty of the whole method lies in the fact that it is very easy to perform the division in hardware, one bit at a time as the serial data goes flying by. There are even LSI circuits which can be used in the hardware of a controller and formatter device.

inexpensive precautions to take to prevent errors:

1. Keep all tapes immaculately clean. Don't ever smoke in their presence. The smoke particulates are murder to magnetic tape.

2. Always rewind tape before removing from the drive. This helps prevent dirt and crinkles from affecting the tape.

Three methods of error detection particularly apply to cassette operations. Only one method need be used at a time. The first technique is the commonly used parity bit. A parity bit is simply an extra bit tacked on to each byte of data. An odd parity system sets the parity bit to one if the one's complement sum of the data bits in the byte is equal to zero. In other words, the parity bit is set equal to one if there is an even number of one bits in the data byte. During a read operation, a new parity bit is gene

rated and compared to the parity bit written previously on the tape. If they are different there is an error somewhere. The disadvantage of a parity check is that it will not detect an error if an even number of bits in a single byte is wrong. Another disadvantage is that a parity bit per byte eats up 11.1 % of the available room for data. For blocks longer than 16 bytes, there are more efficient techniques which use two bytes per block regardless of block length. These techniques are the checksum word and the cyclic redundancy check (CRC) word. The checksum technique simply sums all the data in the block, byte by byte, module 2. The resultant n bit sum is written on the tape as the last information in a block. During a read operation, the data is again checksummed as it enters the computer and the new result is compared to the sum on tape. Again, a mismatch indicates an error has occurred somewhere along the line.

Although the theory of cyclic error codes is somewhat complex for discussion here, the following is a fairly simple explanation of how cyclic redundancy checks work. Consider any random block of data to be a binary polynomial of degree N, where N + 1 is the number of data bits in the block. A CRC check is performed by serially dividing the entire data block (modulo 2) by a binary polynomial of degree 16. Such a polynomial could look like "11000000000000101," which happens to be the standard CR-16 polynomial otherwise represented as X^6 + X15 + \2 + 1. This division process is

Photo J: The works of a Phi-Deck mechanism, viewed from the rear. The four DC motors of the drive can be seen in this photo: Two are used as direct drive for the tape reels, one drives the tape capstan via the puiiy and belt arrangement seen, and the third drives a gearbox which actuates the tape head engage mechanism. For a view from the front, see photo 2.

PARITY SYSTEM

PARITY BIT

DATA BYTE

PARITY BIT

DATA BYTE

TAPE MOTION

PARITY BIT

DATA BYTE

PARITY BIT

DATA BYTE

PARITY BIT

DATA BYTE

PARITY BIT

DATA BYTE

CHECKSUM AND CRC

CHECK WORD

DATA BLOCK

CHECK

WORD

DATA BLOCK

Figure 4: The relationship of error detection data to data constitutes the beginning of a format for the tape data. In a parity system, each data byte has an extra parity bit associated with it, and blocks of data are just groups of such data and parity comb/nations between inter record gaps, In a checksum or cyclic redundancy check system, the data bytes have no detail error detection code associated with them and a single check word, with enough bits to guarantee error detection given the size of the block, suffices. Cyclic redundancy checks are easily generated in hardware, and checksums are the easier route given software as the means of error detection.

illustrated in figure 3. Each unique data block generates a unique 16 bit remainder term after division. The remainder word, or cyclic redundancy check character (CRCC), is written out to tape and is compared to the CRCC freshly generated during a read operation. Once again, a mismatch signifies an error. A CRC generator and checker can be implemented in either hardware or software. Several manufacturers such as AMI, Motorola and Signetics offer LSI chips which do the whole job in one package containing a shift register and some gates, so CRC is best left to hardware. CRC with the 17 bit polynomial is capable of detecting any number of single bit errors and a large portion of any "burst" (multibit) errors that occur in a block less than or equal to 4096 bits long (for a 16 bit cyclic redundancy check code). CRC is fast becoming a standard for floppies and commercial cassette equipment due to its ease of generation in hardware.

The relationships of the error detecting codes to the data they protect is illustrated in figure 4. It is important to keep in mind the completely serial nature of such single track recording.

Tape Transport Hardware

The choice of hardware is another place in which many alternatives are possible. Ordinary audio cassette decks have excellent speed regulation, but they have low tape speed; and included in their price are expensive audio recording and playback amplifiers which are not needed for digital service. In additional, rare is the audio deck which permits digital control of the mechanism. Most decks designed for digital service have good speed regulation, high tape speed, and full digital control of tape motion. Their problem, in terms of amateurs, is price. The majority of digital cassette decks start in the vicinity of $500 for the deck itself and a circuit board with the motion control logic.

Some decks provide tape transfer heads with preamps on the read side; some do not. Most manufacturers offer at additional cost a data encoding and decoding board. Power supplies, although usually trivial, are not cheap. Fortunately, there are currently available several inexpensive cassette decks which meet all of the requirements for digital service. One such unit is the Phi-Deck, from the Triple I Company, which has a current price tag, for the same package mentioned above, of between $200 and $300. The deck itself was originally designed for audio use in a language lab environment where remote control and good speed regulation are important factors. With the addition of regulated high speed (up to 20 inches per

Photo 2: Ira Rampil's homebrew mount for the Phi-Deck mechanism he will be using with his PDP-11/20 system as a mass storage file subsystem.

45

second), the deck is fully adequate for digital use. Since the Phi-Deck is representative of a large class of deck hardware and is itself likely to be the first choice of personal computing equipment designers, a few words could usefully be spent in a description of the deck.

The Phi-Deck obtains its speed regulation from a tape capstan as do audio decks. Many other digital decks use a hub to hub drive technique which then requires a servo loop for speed regulation. The capstan is controlled by a separate motor, as are each of the reels. The head is also controlled by a separate motor to engage and disengage it from the tape. A motion control board receives signals from the processor such as forward, rewind and stop. It converts these control signals into the proper sequence of voltages to control the small DC motors. The control board also relays back to the processor various status lines to confirm that the deck is operating as instructed. The innards of the Super Phi-Deck are pictured in photo 1; photo 2 shows a Super Phi-Deck in a mounting designed by author Rampil for use in his personal PDP-11 based system. Figure 5 illustrates the deck in its relationship to the rest of a cassette memory system.

Data Formatting and Applications

Once a means of recording and recovering data on cassette tape is secured, some decisions must be made on the formatting or layout of data on the tape. There is a wide variety of possible formats. The one to select depends on the application. Whatever the

application, the overall tape format should be as represented in figure 6: clear leader, blank tape, strings of recorded data separated by inter record gaps (IRG), blank tape, and finally clear trailer. Certified digital cassette tapes and cartridges have small holes punched in the tape at the beginning and end of the usable magnetic surface. Essentially, the application dependent variable is the way the data is grouped on the tape. Grouping data into blocks is a key feature of most tape memory systems.

The concept of blocking began as logical records being stored as separate entities on tape. Storing an entire program, for example, as a contiguous string of data separate from other logical records, has some merit. A block has clearly defined starting and end points, and thus eliminates word by word searching through an entire tape to find and process a particular program. As the hardware and the operating systems grew in sophistication, the concept of buffering was applied to input and output operations. Buffering is the process by which data from the outside is first read into a dedicated area of main memory by a monitor program, checked over, and then forwarded to the program which initially requested the data transfer. For example, if a program wishes to read some data points from the cassette memory, a subroutine call is placed to the monitor program requesting the read, the monitor does all the work of finding and reading the data, checks it for errors, and then relocates it to the appropriate locations inside the requesting program's memory

A

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DATA

CODING BOARD

COMPUTER INTERFACE

R/W AMP

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TAPE TRANSPORT

MOTION CONTROL BOARD

CONTROLLER

Figure 5: An overall block diagram of a digitally controlled magnetic film memory subsystem. The addition of complete tape motion control and use of direct digital recording make such a Philips cassette subsystem a vast improvement over the manually oriented lower speed audio versions of tape mass storage. Functionally, this same block diagram applies whether the drive is for a reel to reel tape, a Philips cassette, cr 3M cartridge or other magnetic media. The next step up in erms of performance (and price) is probably a floppy disk. A floppy disk subsystem has a very similar arrangement, but a slightly more complicated motion control section needed to manipulate its movable head.

46

-CLEAR PLASTIC TRAILER -OPTIONAL EOT HOLE

OPTIONAL BOT HOLE MAGNETIC MATERIAL

CLEAR HOLE\ PLASTIC

_ \ LEADER

1^

Figure 6: The anatomy of a Philips cassette recording. At the beginning and end of the tape is a clear plastic leader area. The magnetic tape (symbolized by the black area with dropped out lettering) has an optional EOT (end of tape) hole at each end. Data is typically grouped into blocks, separated by inter record gaps (IRG) which are erased regions without data. The content of the blocks is specified by software and hardware depending upon the particular system used.

space. Although the advantages of buffering 10 are beyond the scope of this article, it should be sufficient to say that they are important. Except in very large commercial machines, buffer areas are seldom large enough to contain an entire program as a single logical record. Therefore, logical records are often broken up into several smaller blocks on the tape. Not only is the requirement for buffer memory reduced; but in addition, error handling is easier. Conversely, if the logical records are very small, for instance, one output character data, the buffering software collects several outputs together and ships it out to the tape as one block. The number of logical records per tape block is known as the blocking factor. Effective blocking represents a compromise between the smallest buffer area and the maximum tape utilization, ie: the minimumnumber of blocks and their associated inter record gaps. A graph portraying the approximate relationship between the length of data blocks, assuming they are all the same fixed length, and the total data capacity of a C-30 cassette is presented in figure 7.

The simplest application lends itself to the simplest formatting. A digitally controlled cassette system or manually controlled system may be used as an inexpensive substitute for a high speed paper tape reader punch. In fact, several manufacturers offer cassette systems that are plug compatible with paper tape equipment. The data is blocked byte by byte, or not at all. Since there is no file structure, the data appears on the cassette exactly as it would on paper tape. There is no need for inter record gaps between bytes in this format, for by placing very long gaps between logical records on the order of a foot or two of tape a human operator can locate a particular logical re

cord with the aid of a tape counter mechanism, just as an audiophile would find a particular song. A UART is a very neat way to generate the parallel-serial data conversion for this byte oriented format. The disadvantage of using a UART here is that it adds at least three extra bits, start, stop and parity, to every byte thus reducing the data density on the tape.

For more efficient and useful operation, a file structure should be added to the digi

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Figure 7: Cassette capacity versus block size. The inter record gap (IRG) is essentially wasted space on the tape. By increasing the size of the block, the percentage of tape wasted on IRGs declines toward a limit of zero. As the size of the block is decreased (ultimately to its limit of a single byte separated by IRGs on either side) the total number of bytes available on a tape declines. For any given set of parameters (inter record gap length in inches, flux density in bits per inch, and data format), the total useful data per cassette can be calculated and plotted as one point on a curve such as this.

47

tally controlled transport. By blocking the data into chunks of convenient size with identification information, software can then examine each buffer as it is read in to search for any particular file (a group of such blocks) on the tape. A file is considered to be a single logical record even though it might cover many blocks. In a file structured system with a remotely controlled tape deck, keyboard commands or commands generated by a program replace manual intervention and the automatic operations make the system much more convenient. Still lacking, however, is a very useful block replacability feature since there is no way to synchronize the start of overwriting with the

FOR FURTHER READING

Books

Bycer B 8, Digital Magnetic Tape Recording: Principles and Computer Applications, Hay den Co, NY 1965. This book has an excellent introduction to the theory, but the chapters on applications are heavily dated.

Sebestyn, L G, Digital Magnetic Tape Recording for Computer Applications, Chapman and Hall Ltd, London, 1973, an unimposing but very usable modern reference; a book shelf must for the designer types.

Commercial Literature

1. Memodyne Corp, Newton Upper Falls MA, "Recording Binary Code on the Philips Cassette," an 11 page brochure.

2. MFE Computer Access Systems, Salem NH, "Applications Notes #63 to 66" a pro and con discussion of cassette decks and recording techniques.

3. Motorola, Mesa AZ:

a) "M6800 Microprocessor Applications Manual," includes the complete design of a possible cassette memory system including software.

b) "Phase Locked Loop Manual," discussion of using PLLs for PE decoding.

c) "MC3467, MC3468 Applications Notes," monolithic magnetic tape read chains.

d) "MC4044 Applications Notes," using a PLL phase detector in PE decoding.

e) "MC8521 Preliminary Data Sheet," not yet released, but a complete PE decoder on a chip.

4. RCA, COS/MOS Data Book, "Applications Note ICAN6101, ICAN6210," PE decode/ encode using CMOS.

Acknowledgements

The authors would like to thank the following individuals and groups for their gracious generosity and assistance:

Joe Roy, Motorola

Paul Nordeng and the DASL Staff, University of Wisconsin

The Economy Company.

beginning of a data block, especially if the drive has stopped in the preceding gap. Although it is not possible in this system to overlay a corrected or updated program into the space it formerly occupied, it can easily be added on to the end of the tape.

Musings on the Ultimate

The ultimate cassette memory system incorporates block replaceability and sector addressing to simulate random access storage. The technique proposed here for PhiDecks is similar to that used so successfully by Digital Equipment Corporation in their DECtape units. In fact the Sykes Corporation developed and marketed such a system for cassettes until their attentions turned to floppy disks. The trick is use one track for normal phase encoded or pulse ratio data and a second track as a prewritten mark track. The mark track is first written to initialize the tape and it is only read thereafter. It contains, in the same code as the data track, various sorts of delineators, or marks, and also the block address numbers of the data blocks residing on the adjacent data track(s). Data is written in fixed sized blocks in synchronization with the areas designated by the mark track. By observing the transitions on the mark track, the tape controller wilt have no difficulty in overlaying or replacing previously written data. The advantage of including block numbers on the mark track is that as they are read in, they can easily be compared with a register containing a block number being sought, thus eliminating the need for a software search program. Usually a directory data block is included on the tape, most frequently as the first data block. Its contents generally include the file names and their starting block addresses. When a cassette is first mounted in the drive, its directory is read in. Whenever the computer needs access to a tape file, it gets the block address from the directory and initiates a hardware search. Each time a change is made to the tape, the directory copy in memory is updated and a copy of it is written back to the tape. Using one's imagination, many different file manipulations are possible with such a system. Anything possible with a floppy disk operating system is in fact possible with a mark track cassette system. The tradeoff is just time versus price. A floppy is essentially instantaneous, from a human standpoint. A cassette system takes from seconds to a few minutes, at about one fourth the price of a floppy. Even with these time constraints, a full digital cassette system is a lot less painful than Teletype paper tape or audio cassette."

48

j^*t ;Sti!«&& ;*»*»

^ v

FROM THE

Full 16K of memory on one card available in 4K increments. Buy only what you need now. Expansion later is easy with a board you have already tested.

Utilizes the EMM SEMI 4200 memory chip which is organized as 4K by 1 bits. Provides maximum access time of only 200ns. Added to board logic time, total board access time is below 250ns. No other memory board made to S100 bus specs can match this.

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Each 4K block may be individually addressed at any 4K page border. You have the versatility of most 4K boards in your 16K package. Address changes are very easily accomplished by using a simple jumper scheme. Each 4K block may be individually protected by a switch.

Power consumption is outstandingly low! Only 205ma from the +8v, 105ma from the + 16v, and 24ma from the - 16v, for a FULL 16K. Battery backup with a simple jack connector.

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Fully solder masked and silk screened board, sockets for all IC's. Complete documentation includes source code for comprehensive memory test program and paper tape of this program.

KIT: 4K - $169; 8K - $295; 12K - $435; 16K - $574; 4K expansion kits - $140.

16K assembled and tested: $644. Delivery: Off the shelf to 30 days.

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<"***

fi

What's Involved in Kit Building?

A collection of typical tools useful In building a kit This collection Includes several sizes and types of screwdrivers, needle nose pliers, side cutter (diagonalsJ} a set of nut dri vers, pliers, wire stripper, knife, soldering iron and solder. A solder removal device, such as a bulb sucker or a mechanical action suckerf is also most useful.

Louis E Frenzel

1588 Oak Ter

St Joseph Ml 49085

Most of the personal computing equipment available to the hobbyist today is in kit form. As a result, the field of personal computing as it is now known essentially centers around the building, testing and troubleshooting of computer kits. Many individuals with a "computer hobbyist" approach to the field are electronic types who enjoy kit building and consider their work with the equipment to be the main focus of their interests.

However, many other people would rather concentrate on the programming and application of the equipment. Such individuals may not enjoy or even consider themselves capable of building some of the sophisticated computer kits available. Yet

many of these nonhardware types are taking a chance on their being able to successfully learn kit building. They do so simply to be able to have the equipment that is available today. At this point in the development of the personal use computer field, being able to build a kit often means the difference between being able to own a fairly sophisticated computer or not.

There are many benefits to be gained by building a kit. Kit building is something that can be learned and easily mastered even by individuals who do not know and understand electronics. The purpose of this article is to outline the benefits of kit building and to present some basic guidelines and procedures that anyone can learn to successfully

50

Kit building is something that can be learned and easily mastered even by individuals who do not know and understand electronics . . .

construct a kit. The personal use computer field will continue to remain essentially a kit business for the immediate future. Why not join others in experiencing the benefits that come from this activity?

Benefits of Kit Building

Most inexpensive computer equipment is available in kit form because sometimes this is the fastest and easiest way for a manufacturer to develop and offer the product. This has allowed many small companies to enter the market quickly. Kits have been largely responsible for expediting the growth of hobby and personal computing by allowing young manufacturers to sell more products sooner.

While kits offer benefits to the manufacturer and to the builder overall, the real benefits of kit building go to the builder. Some of the benefits are obvious, but others are more subtle. Let's consider them.

Save money. One of the obvious benefits of purchasing kit equipment is the resulting savings in money. Kits almost always cost less than equivalent wired and tested products simply because the cost of labor is removed. In some cases, the price of a kit can be as low as one half the assembled price. Such savings are significant and have often made the difference between an individual being able to afford a computer or not. The cost savings has further benefited the field by allowing many more individuals to participate. It certainly makes sense to assemble the equipment yourself if you can. For a given upper limit dollar investment, you can afford significantly more equipment if you purchase kits.

Pride of accomplishment. A benefit not as obvious to those who have never built a kit is the sense of achievement that it produces. This is particularly true of large, complex and difficult kits. When an individual successfully assembles a sophisticated kit and makes it work, he or she is rewarded with a real sense of accomplishment. This is a feeling that is hard to describe, but one that becomes obvious when you build your first successful kit.

Fun and enjoyment. This is a do it yourself age. Most people enjoy doing things for themselves if they can. There is a certain amount of enjoyment in tuning your own car, growing your own garden, or paneling your basement. The same is true in the computer field. People want to do it themselves and find enjoyment in it. Kit building as a hobby fulfills this need for fun and involvement. Like other hobbies, kit building is relaxing since you become occupied in an activity that demands your full attention and skill. It takes your mind off other problems and worries.

Learning. One of the most subtle benefits of kit building is learning. Whenever you put a kit together and make it work, you automatically learn more than you realize. The whole process of kit building is educational. This is particuarly true for those individuals who are not electronic experts. Beginners quickly learn basic skills such as soldering, identifying electronic components, theory of operation and basic testing and troubleshooting methods. The learning may not be obvious as you are constructing the kit, but it is there and sooner or later you will realize it.

Kits can: save money, give pride of accomplishment, provide fun, enjoyment and learning, and prepare the owner for maintenance.

Lou Frenzei has been an enthusiastic personal computing advocate of the

"build it yourseff" variety for some time. His personal systems presently include an IMSAJ8QS0 kit product with 8 K of memory, an evaluation board 6800 system from Motorola with enough additional memory to run Tom Pittman's Tiny BASIC, an ASR 33 Teletype, audio cassette interfaces, serial and parallel inter faces for custom peripherals. One projected application for the computers is to amateur radio, where he aims to use the processors for station control, and processing of message and logging data for his station, W8LJR. Professionally, Lou is Director of Computer Products for the Heath Company, a firm which started the electronics kit business as it is known today. *

51

A "beginner's" kit assumes no knowledge of electronics and is exhaustively documented.

An "experienced builder's" kit assumes some knowledge and familiarity with electronics and as a result is less expensive due to savings in documentation cost.

Preparation for maintenance. Electronic equipment is much easier to service, repair or modify if you are familiar with it. Once computer equipment has been assembled and made operable, it is generally reliable. But should service be required, it will be easier if you know and understand the equipment. Kit building gives you much of that knowledge and familiarity.

These are only a few of the most important benefits of kit building. If you want total involvement from your use of computers, you should participate in as many of the different facets of it as you can. Kit building is one of the best ways of achieving this participation.

Types of Kits

All kits are not equal. There are big kits and little kits, easy kits and complex kits. In addition, there are different types of kits depending on the approach taken by the manufacturer and the intended customer. Before you purchase a kit and attempt to assemble it, it is a good idea to be aware of the types of kits available.

There are two broad, general classifications of electronic kits, those for beginners and those for experienced hardware people. These classifications really represent the extremes of a range of types of kits; but for purposes of discussion such "ideal types" are useful. Kits designed for the beginner are generally simpler and more thoroughly documented. Even an individual who knows nothing about electronics can usually assemble such kits successfully. The assembly, test and troubleshooting instructions are thorough, take nothing for granted and lead the kit builder by the hand through a step by step process of assembly. With such a kit, most people have little or no difficulty in assembling the product and getting it to work regardless of their knowledge and experience. Even though you may not be a beginner, this type of kit is often the best in terms of value because it practically insures hassle free building and a workable end product.

Another type of kit is one designed for the experienced kit builder or electronics expert. Such kits are furnished with a minimum of documentation and assembly instructions. In some cases only a schematic diagram, a printed circuit board layout showing component placement, and a parts list are supplied. To an experienced builder, this is usually sufficient information to assemble the product and get it to work properly. Many of the computer hobby kits available today are of this type. They assume that the builder is familiar with such equip

ment or it would not be purchased in the first place. Many novices and beginners have discovered this too late. There's nothing wrong with this type of kit because it does produce a useable end product. The problem comes when an inexperienced builder attempts to construct a kit of this kind and makes mistakes due to either lack of knowledge or experience. Such kits are highly desired by the experienced builder because they give him far greater satisfaction and a feeling of more involvement than the simpler kits, and ultimately have a lower cost since "idiot proofing" the documentation is a significant cost item in any kit. Experienced electronic kit builders receive great satisfaction from using their knowledge and experience in such projects. Many even enjoy discovering errors or having to supply missing information. They like to do the research necessary to build a product successfully. What may be a problem and big frustration to some is a real challenge and enjoyment to others.

Qualities of a Good Kit

Just what are the qualities of a good kit? It is desirable to know the elements of a good kit so that when you evaluate a product or compare competitive units, you will choose the best product for you. Here are several things you should look for in choosing a kit product.

Well designed. This is a subjective point yet an important one. A good design is one that works, has proven itself reliable and accomplishes its purpose. Other elements of good design involve the use of modern components and techniques. Good design is difficult to assess if you are not familiar with the specifics of the equipment or the latest technology. However, good product design generally shows up as a good reputation in the field, positive comments from owners, and favorable magazine test reports. If you are a newcomer, read every scrap of literature you can find, talk to people at your local computer club, and keep an open mind!

Good documentation. Just as important as good design is good documentation. This is an absolute necessity for a successful kit. The manufacturer simply must supply sufficient information to build, test and apply the product. Poor documentation usually means the difference between a good kit and a bad kit. A well designed kit can be bad because poor documentation makes it difficult if not impossible to assemble and use. Look for and insist upon good documentation to the level of detail you require.

Quality components. Quality or first grade components are a major part of any

52

Some Typical Introductory Kits

The Heath Company is the oldest and largest manufacturer of kits. For those computer people who are wary of trying a complicated kit, author Frenzei suggests several of his company's products as a means of seeing what it takes to build a kit by trying out the concept on simple items. Each of these items will result in a useful accessory for the computer lab, as well as introducing the builder to the process of building kits.

a. A prototyping breadboard. In computer applications, such a breadboard can be used to temporarily try out a circuit before committing it to permanent form using wires, sockets, Vectorboard and solder or wire wrap. Power supplies at standard logic (+5 V) and typical analog (±12 V) levels aid prototyping with this unit.

good kit. If a manufacturer uses regular commercial grade components, then the quality is good. Quality components help insure reliability and a minimum of defects and problems in assembly. Kit suppliers can sometimes purchase surplus or degraded components at significant savings. As a result they can pass along major cost savings to you. While lower cost is certainly a significant benefit, it is often offset by the problems encountered by the poor component quality. Unless you are prepared to deal with the limitations and problems brought about by low quality components, it is best to stick with the higher priced but more reliable units using quality parts.

Designed as a kit. Many products are not designed to be kits. Such products are designed first to have specific features and to meet certain performance specifications. The fact that it is to be offered in kit form is often secondary. The designer's main purpose is to achieve a saleable and workable product. Once this has been done, many designers feel that it is only necessary to supply the components in a bag which the customer can assemble. If the product is designed as a kit, the designer is constantly reminded that the product must be easy to assemble and service. For that reason, kit design and thorough documentation is some

b. A laboratory bench power supply. Once built, this instrument is used to simultaneously power logic (+5 V) and provide variable metered analog levels from ±0 to ±20 V.

c. A multimeter. This ail around useful test instrument can be built from a kit and later used to measure miscellaneous voltages, current and resistance when diagnosing or using the hardware of a computer and its interfaces.

what more difficult and time consuming than designing equipment that will be manufactured. Such products generally come from those manufacturers dedicated to the kit business.

Manufacturer support. A good kit manufacturer is one that supplies plenty of service and support. A customer can make wiring errors, receive a defective component or simply have difficulty in interpreting the documentation. The customer must have some way of dealing with these problems if he or she is to be satisfied with the product and complete its assembly. Always look for a kit manufacturer which has a significant amount of backup. This means the manufacturer will answer your letters and telephone calls regarding problems. In addition, the manufacturer should offer complete service and repair facilitiies at reasonable prices. Also check the warranty. Before you purchase a kit, be sure that you satisfy your own requirements with regard to the support and service available.

These are the main qualities of a good kit. Before spending hundreds or even thousands of dollars on computer equipment, investigate these points carefully. Your satisfaction with the products will be greater if you do.

A good design is one that works, has proven itself reliable, and accomplishes its purpose.

53

WMW'i

Key J: A low wattage soldering Iron is a must for building computer kits (or any kit with delicate printed circuit runs). Here is a typical low wattage iron with a small tip, along with a suction bulb device which can be used to remove solder if necessary.

Photo supplied by the Heath Company

Read test reports on the products that you are considering. Ask friends, associates and fellow club members for their opinions on the product. Often the experiences of others can help you decide. Also get as much information from the manufacturer as you can. If the data sheets and catalogs supplied are insufficient, write for further information. A reputable manufacturer will answer your specific questions and provide additional information as required.

One of the best ways to size up a product is to purchase the documentation for the kit. Most manufacturers will allow you to purchase the assembly and operation manuals. This will give you full details on the product and will give you an advanced look at the assembly instructions and other information. If you're serious about a product, this is a small investment to make to insure that you obtain a good product.

Building the Kit

Here are some tips, based on experience, that can help you build kits successfully even if you are a beginner:

Practice first. Before you wade into a $1000 computer kit, perhaps you should test or improve your skills first on a simple, low cost kit. This is particularly true if you are a novice. If you have never assembled a kit before, start out with a small, easy to build project first. You will learn a lot by assembling this simple project first, and you will get a feel for what kit building is all about.

There are a wide variety of simple low cost kits available. Many accessories and pieces of test equipment fall into this category. Try to choose a project that will be useful to you when you get to the computer kit, or in some other way. A good example of equipment that could be of value to you when working with computers is a volt ohmmeter or a power supply. Both of these items are relatively easy to build and you will find much use for them later when working with your computer system.

Obtain the proper tools. You will need a variety of tools to build a kit successfully. There is nothing more aggravating than to come to a point in the assembly process where you do not have the tools needed. While most kits can be assembled with common tools, you should provide yourself with a minimum set prior to building your kit. It will make the kit building process go faster and easier. Here is a list of the most common tools you will need:

1. screwdrivers of several sizes: blade and Phillips types

2. needle nose pliers

3. side cutters

4. nut drivers (0.25 inch is the most useful.)

5. pliers

6. wire strippers

7. knife

8. soldering iron

9. solder

10. solder removal device

Learn to solder. The most important skill required to build a kit is soldering. The majority of computer equipment is constructed by attaching electronic components to printed circuit boards. The circuit boards are then interconnected to one another through other printed circuit boards, connectors and cables. Solder is the common bonding element in all cases. You simply must learn to solder if the kit is to work properly.

Soldering is the process of melting an alloy of tin and lead known as solder, wetting the component leads with the hot molten solder, then allowing it to cool and provide a permanent electrical interconnection. The components to be joined are brought together physically and the joint made mechanically secure. Then a soldering iron is touched to the joint so that the component leads are heated. Once the joint is hot enough, solder is applied and allowed to flow over the connection. Then the heat is removed and the solder is allowed to harden. The result is an excellent mechanical and electrical connection.

54

To solder properly, you must have the right equipment. Primarily this means a soldering iron and solder. For most electronic construction, a small, low wattage, hand held pencil type soldering iron should be used. One with a wattage rating of 25 to 40 watts is best. This will provide more than sufficient heat but at the same time is low enough in wattage to prevent damage to electronic components. The soldering iron should also have a small, fine tip so that solder can be successfully applied to the very small connection pads on most computer circuit boards.

The type of solder used is also important. Many kits are supplied with the proper solder. If solder is supplied, use it. If you buy your own, be sure to purchase quality electronic grade solder. The best is a 60-40 rosin core solder. The 60-40 refers to the percentages of tin and lead respectively in the solder. The rosin core means that the solder contains a cleaning element that helps to remove the oxidation from the connections when heat is applied. (Do not use acid core solder which can destroy electronic components. It will literally digest your computer.)

The size of the solder is also important. For the tiny circuit board work found in most computer products, a thin solder is best as it is easier to control the rate of flow. Solder smaller than 0.032 inches in diameter is best. This will prevent excess solder from

being applied and will reduce the possibility of making solder bridges.

Next you should develop your soldering skills. The best way to do this is to practice. The proper procedure is to first physically connect the components. Usually this involves bending the leads of the component and mounting it on a printed circuit board. The soldering iron is then used to heat the junction of the component lead and the foil on the printed circuit board. It takes only several seconds for the joint to become hot enough to melt solder. Solder is then applied to the junction and allowed to flow over the leads and copper foil. The solder and iron are removed and the connection is allowed to cool and harden.

While the procedure sounds simple, it is a bit subtle. The subtlety has to do with the amount of time you heat the junction prior to applying solder and the amount of time the iron is left on the joint after solder is removed. If you apply too much heat in the beginning you can damage the component or cause the copper foil on the printed circuit board to peel off. Yet if you do not apply enough heat, the joint will not become sufficiently hot to melt the solder properly. If the solder is not melted thoroughly it will cause a so called "cold solder" joint. These are conditions where proper bonding does not take place. The amount of time that the heat is applied is a balance between that which prevents damage and that which

Simple points: Practice first, obtain proper tools, learn how to solder, learn how to unsolder, and if all else fails, read the directions.

One of the best ways to size up a computer product is to purchase the documentation (or borrow it from a friend). This is true whether the product is in kit form or not. (A corollary is the thought that good looking and complete documentation is an excellent sales tool for the manufacturer.)

Key 2: One key to good soldering is a clean soldering tip. There are several different brands of wet sponges like this one, which can be used to clean the tip during use. Many of these products are treated with special chemicals to help improve the cleaning properties.

Photo supplied by the Heath Company

55

allows the solder to melt and flow as it should. The skill and timing in this operation comes only from practice.

Learn unsoldering. Another skill practically as important as soldering is unsoldering. It is often necessary to remove a component from a printed circuit board. The component may become defective and need replacing. Or you may have discovered that you connected the component incorrectly. If you learn the technique of unsoldering, the component can be removed without damaging it or the printed circuit board.

Unsoldering is best accomplished by removing the solder on the connection. Do not attempt to remove a component by simply reheating the connection and prying the component from the printed circuit board. Damage will usually result. Although it takes a little more time and care, removal of the solder first will insure that you do not

Key 3: Use proper soldering technique. This set of iliustrations provided from the Heath Company documentation of kits illustrates proper soldering technique when assembling circuit boards. As noted at the bottom, it is important to heat both the component lead and the printed circuit board contact. If either is missed, then a bad joint as at B or C could result.

damage either the component or the printed circuit board.

Solder can be removed from the connection by first heating the connection with your soldering iron and and then using a suction bulb. This is a device designed to pull the solder from the connection by a vacuum created in a rubber bulb. A plunger type device known as a solder sucker can also be used.

It may take several applications of the tool to remove all of the solder. Get as much off the connection as you can. Then use a knife or needle nose pliers to carefully break the component lead loose.

Another method of removing solder from a connection is to use a wire braid coated with rosin. The braided wire is coarse and

1. Place the soldering iron tip against both the lead and the circuit board foil. Heat both for 2 or 3 seconds.

SOLDERINGA I RON

COMPONENT LEAD<

RCUIT BOARD

2. Then apply solder to the other side of the connection. IMPORTANT: Let the heated lead and the circuit board foil melt the solder.

3. As the solder begins to melt, allow it to flow around the connection. Then remove the solder and the iron and let the connection cool.

SOLDERING IRON

4. Hold the lead with one hand while you cut off the excess lead length close to the connection. This will keep you from being hit in the eye by the flying lead.

Be sure the solder made a good electrical connection.

When both the lead and the circuit board foil are heated at the same time, the solder will flow onto the lead and the foil evenly. See Illustration A. The solder will then make a good electrical connection between the lead and the foil.

When the lead is not heated sufficiently, the solder will not flow onto the lead as shown at B. Reheat the connection and, if necessary, apply a small amount of additional solder to obtain a good connection as shown at A.

When the foil is not heated sufficiently, the solder will blob on the circuit board as shown at C. Reheat the connection and, if necessary, apply a small amount of additional solder to obtain a good connection as shown at A.

SQLDEk FLOWS OUTWARD

AND GRADUALLY BLENDS WITH THE FOIL AND THE LEAD.

®

SOLDER DOES NOT FLOW ONTO LEAD. A DARK ROSIN BEAD SURROUNDS AND INSULATES THE LEAD FROM THE CONNECT ION,

SOLDERING

IRON POSITIONED CORRECTLY

BURNED / / ROSIN /> '

// / SOLDERING * , , *Sl iron ''-"'' POSITIONED

INCORRECTLY

SOLDER APPEARS TO FLOW INWARD AND STF ON TOP OF THE FOIL.

SOLDERING

IRON

POSITIONED

INCORRECTLY

56

can soak up a lot of solder. The rosin cleans the braid and the connection and encourages the capillary action that literally slurps the solder off the connection. To use the braid you simply place it on the connection and heat it with the soldering iron. The solder will flow up into the braid leaving the connection clean and open. Again, several applications may be necessary to remove all of the solder. Solder removal braid is available at most stores selling soldering irons and related equipment. It is extremely effective and will save you much time and possibly some expensive components and printed circuit boards.

Follow directions, it seems almost ridiculous to point this out, but one of the most common faults of kit builders is not following the assembly instructions. The assembly instructions have usually been tested to insure that they work. If you use a different assembly sequence or fail to note some of the special instructions, you are most likely to make a mistake. Even though you may be

an experienced kit builder, sometimes there are subtleties in the assembly process that make it absolutely essential that you follow the given directions.

Another precaution is to look for any errata sheets or correction notices before you begin the assembly. Some errata sheets are included randomly or at the end of the supplied documentation. Don't take chances; catch the errors in the documentation first to avoid mistakes.

Don't ruin your investment by assuming that you can do it by yourself. Protect your investment and follow the instructions. Remember the old saying, "If all else fails, read the instruction manual," is true.

Take your time. When building a kit, take your time. The faster you go the more likely you are to make a mistake. Most people who purchase kits are anxious to put them together and use them. This is only human and certainly understandable. But unless you have patience and take your time to follow the instructions and do quality work, your

Use of sockets remains a highly recommended practice — but use quality sockets by all means.

Key 4: If you make a mistake, fix it. To remove solder, use a bulb sucker (see key 1), a mechanical solder sucker tool (a), or a solder removal braid (b).

(a) Photo supplied by the Heath Company

(b) Photo courtesy of Wik-lt

I

57

(a)

Key 5: A detailed solder braid removal sequence, supplied by Wik-lt (a) Find the connection to be desoldered. (b) Heat the connection through the braid, causing capillary action to suck up the solder, (c) Remove soldering iron and braid, to view the desoldered connection.

(b)

(c)

chance of achieving a successful build are much lower. A better end product will result if you take care and time.

Part of the concept of taking your time is to spread the kit building process out over a long period. It is a lot better to have eight one hour or four two hour kit building sessions than it is to have a single eight hour session. The longer the kit building session, the more mistakes you are likely to make. When you find yourself getting tired, losing interest, or attempting to short cut the instructions, stop. Go back to building when you have had a chance to rest.

While it's good to take your time in building a kit, just keep in mind that most kits come with a limited time warranty. Thirty and ninety day warranties are typical, so it is highly desirable that you assemble the kit in less than that time. If you discover any defective parts or other problems, you can get them replaced within the warranty period. Take your time, but don't lose the benefit of any warranty that you may receive.

Ask questions. As you're building a kit you may have questions about the assembly. If the instructions are not clear or problems arise, don't guess. Don't take anything for granted. Attempt to answer the question yourself, of course. Study the directions more carefully. Ask a friend who has built a similar product. Call or write the manufacturer to be sure of what you're supposed to do before you go on. You can save a lot of time, money, grief and dissatisfaction if you get answers to questions before going ahead with what may be an incorrect decision.

Use sockets. Many electronic kits do not supply sockets for the various components. Transistors, diodes and integrated circuits are usually soldered directly to the printed circuit board. Some of the more expensive and delicate components may use sockets. While sockets may not be supplied, it is generally a good idea to add them yourself. The sockets will allow you to remove components for troubleshooting purposes or to replace them if they become defective. The socket will add a little extra cost to your kit, but the advantages are worth it. The ease with which a product can be serviced when all of the integrated circuits are in sockets is excellent. It is one investment that you may question in the beginning but will certainly find worthwhile later should you have difficulty. If you choose to use sockets, however, be sure to use high quality new sockets, preferably with gold or other nontarnishing finish on the contacts.

Provide yourself with reference resources.

58

Many manufacturers supply all the information needed to construct the kit successfully. Additional information simply is not necessary. But there are some kits that require you to have additional information. For example, it may be necessary for you to know the pinouts or theory of operation of the various TTL or MOS integrated circuits used in the kit. Because of this, it is a good idea to provide yourself with a reference library of books, catalogs, data sheets and any other information you can get your hands on. You will also find general textbooks and application notes from the integrated circuit manufacturers to be helpful. When you run into trouble or have questions, your references can provide the answers. It is an excellent investment that you should make at the time that you purchase your kit.

Two of the most important references you should have are the Texas Instruments TTL Data Book or its equivalent and the catalog or data sheets from the manufacturer of the microprocessor used. Adam Osborne's series of microprocessor books are particularly good and will also make excellent background reference sources.

Be careful with components. Most electronic components are small and delicate. They can be easily damaged physically and most can certainly be destroyed by excessive heat. Diodes, polarized capacitors and most integrated circuits can be put in backwards which would cause improper operation and possible electrical damage. Integrated circuit pins can also be bent and broken off very easily. Be very careful with every component as you install or solder it.

Another important precaution concerns the installation of MOS integrated circuits. These devices can be destroyed by static electricity. A static charge can be transferred to a MOS device by your hand or the soldering iron. Most MOS devices are supplied mounted in protective foam to keep the pins shorted. Leave the devices in this foam until you are ready to install them. When you do, be sure you ground yourself or remove any static charge before you pick up the device. If you use sockets, the MOS damage from static charges can be greatly reduced. Any charge from the soldering iron will be dissipated in mounting the sockets, not installing the integrated circuits. Further, when installing the integrated circuit in the socket, you can short all the leads together by pressing the board and socket against conductive foam.

All of the above recommendations and precautions are obvious for the most part. It's easy to read them and agree with them,

Provide yourself with a library of reference information about computers, integrated circuit logic data, etc. It will prove to be one of the most valuable pieces of "equipment" in your personal computing endeavors.

but if you are to assemble your kit successfully, you absolutely must follow them. It's a small price to pay for protecting your investment.

What to Do If You Have Trouble

Whenever you purchase a kit you should prepare yourself for the fact that you may make a wiring mistake or encounter a defective component. If you plan for this in the beginning you will not be surprised if it happens. In most cases you will find that it is not a serious problem. Instead it is simply an inconvenience to overcome. If you approach it with the right attitude, you will not be dissatisfied with your kit. Here are some tips on what to do if you experience difficulty.

When you finish building the kit, follow the test, checkout and troubleshooting instructions given by the manufacturer. The quality of this information varies from one manufacturer to another. Some supply no information while others furnish detailed troubleshooting charts. Use whatever information is available to you first before going on with the recommendations given below.

Question the problem. The first thing to ask yourself: Is the trouble you experienced really a problem? It may indeed be, but it may also be that you are using the equipment improperly. The controls may have been set incorrectly or you may be wrongly interpreting the results. The solution to this is to read the instruction manual carefully to be sure that you are doing things properly. In computers, as in flying, cockpit problems or pilot errors are a typical source of trouble. The hardware may be good, but the operator may be defective. Even in simple kits this is a very common problem. Due to the complexity of computers, no kit will be totally immune from this problem.

Check your assembly. Once you have eliminated operator error as the trouble, you can assume that you have a hardware problem. The first suspect is assembly errors. Go back and double check your assembly. This is time consuming but it can often turn up the problem. A good way to do it is to have a friend help you. Often by working with someone else you can find the problem

59

Be sure to remember the motto of a certain very large computer company: THINK. The application of computers as general purpose problem solvers requires thought on the part of the user, whether the computer is a kit or a traditional high priced product. The only computers which have any hope of being totally "idiot proof" are those which have had the thought requirements distilled into a well designed application program in products such as a hand calculator, a microwave oven controller, a "turn key" application system or any situation where the programming is supplied in a packaged solution to a problem.

that you may have overlooked yourself. A common mistake is poor solder connections. It may be difficult to spot one bad solder connection among thousands, and even a bad solder joint sometimes looks good. As a result, the first step should be to resolder each and every connection in the kit. Again this is tedious but will often solve the problem. To do this, simply touch the soldering iron to each solder connection briefly to remelt the solder. If you see a wisp of smoke come out of the connection, it may indicate that the rosin in the joint was not sufficiently melted thereby causing a poor connection. The joint may have been a cold solder joint where no electrical continuity existed at all. Simply reheating the connection made it good.

As you are resoldering the connections, look for solder bridges. This is a thin trace of solder that is accidently drawn between adjacent pads on the circuit board. The solder bridge causes a short. These bridges are usually eliminated as each solder connection is reheated. But they may not be. As you are resoldering each connection, look carefully at adjacent pins to be sure that shorts do not exist. Some solder bridges are so fine that they are difficult to find. Use a magnifying glass and strong light to help. As you go through a complete circuit board you may discover connections that you forgot to solder or components that did not get installed properly. Simply resoldering all the connections is an excellent way to recheck your assembly since it methodically covers all points.

Once you have double checked your soldering and assembly, again test the equipment. Many times the problem will be solved and proper operation will result. If the difficulty still exists, the problem may be a defective component. Unless you have had specific experience in troubleshooting electronic and digital equipment, locating a defective component can be difficult. For that reason, it is best to call for help.

Seek help. The first step is to ask a friend or the manufacturer for help. You may be able to find a friend who has built a similar piece of equipment or who has experience in troubleshooting. Don't hesitate to call or write the manufacturer for help. It is the manufacturer's responsibility to help you get the kit working properly.

Another alternative is to seek help from your local computer store. Most store owners will be familiar with common problems and may have just the advice, information or help you need.

Before you ask for help, however, it is best to isolate the problem yourself if you

can. Write down all of the symptoms. Make some tests yourself to try to determine what is happening or not happening. If the processor runs at all, run some simple diagnostic programs to attempt to isolate the problem. Try to obtain as much information as possible before you ask for help. The more information that you supply the better the quality of the help that you will receive. For example, one of the things that you can do is measure the power supply voltages. Often the equipment is not working simply because it is not receiving power. Use a voltmeter to check power supply voltage at each of the printed circuit boards in the equipment. If an oscilloscope is available, check for the presence of clock pulses.

Once you have accumulated as much information as possible, write a letter or make a phone call to the manufacturer. Continue this process until the trouble is located. If all else fails, return the kit to the manufacturer or your local computer store for repair. Above all, don't give up. The real fun begins when you get your computer running.

Kit Versus Wired Products: Your Decision

Kit building is fun, challenging and satisfying. It is educational, and you can save a lot of money. Most people who have built kits successfully highly recommend it. Yet some computer hobbyists simply do not want to spend the time or become involved with kit building. They want to concentrate on programming and applications. It is probably best that these individuals buy wired and tested units. Although this reduces the number of products available, it does eliminate the potential problems associated with kit building. It also eliminates the benefits.

Before you decide to buy a wired product, you should also consider having a friend or other individual build the kit for you. Often you can locate someone who is willing to build a kit for a price far lower than you would pay for an assembled unit from the manufacturer. I have heard of several examples where individuals have assembled kits for others simply to be able to have the experience of building and using the kit themselves for a period of time. There are a number of small companies who are in business to build kits for individuals. The prices are usually less than the assembled and tested units available from the manufacturer.

Even though you may have shied away from building a kit, try it. You may find that it is easier and more fun than you suspected."

60

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1276

Articles Policy

BYTE is continually seeking quality manuscripts written by individuals who are applying personal systems, or who have knowledge which will prove useful to our readers. Manuscripts should have double spaced typewritten texts with wide margins. Numbering sequences should be maintained separately for figures, tables, photos and listings. Figures and tables should be provided on separate sheets of paper. Photos of technical subjects should be taken with uniform lighting, sharp focus and should be supplied in the form of clear glossy black and white or color prints (if you do not have access to quality photography, items to be photographed can be shipped to us in many cases). Computer listings should be supplied using the darkest ribbons possible on new (not recycled) blank white computer forms or bond paper. Where possible, we would like authors to supply a short statement about their background and experience.

Articles which are accepted are typically acknowledged with a binder check 4 to 8 weeks after receipt. Honorariums for articles are based upon the technical quality and suitability for BYTE's readership and are typically $25 to $50 per typeset magazine page. We recommend that authors record their name and address information redundantly on materials submitted, and that a return envelope with postage be supplied in the event the article is not accepted."

Continued from page 14

perhaps the extreme case for shipment of BYTE magazines to foreign subscribers. Not satisfied with waiting three months or so for the very current information we put out in BYTE each month, he started immediately to search for alternatives.

His first urge was to import BYTEs in sufficient quantity to sell to his neighbors in the Sydney area, thereby assuring (so the theory went) that he got them on a timely basis by way of a bulk shipment. With that in mind, he figured that he'd send them air freight to his shop, then distribute them. Nice theory, but, in bulk it cost US $1.50 or more to ship each magazine by air — so his bulk shipments ended up going on the same boats which carry the surface mail. (It costs nearly US $6 to send just one copy by air mail!) So much for that theory. After taking a bulk shipment of BYTE each month for several months, John hit upon another solution to the problem: Maybe he could talk BYTE into printing locally for distribution in Australia. Shortly after that brainstorm struck, we got our first long distance phone call from John Bannister.

Phone calls from Australia are most interesting. You'd expect that a certain decay in quality would occur as the distance increases. But much to our surprise, the phone conversations with John, whether by cable, radio or satellite, often came through with a quality perhaps half an order of magnitude better than a simple transcontinental conversation with an advertiser in California! Of

course, for such calls, either one party or the other is bound to be half asleep, for the time differential is 11 hours between EST and the time zone which encompasses Sydney. At any rate, the first phone call was to explore the possibility of setting up a new Australian publishing house with John as the principal, whose purpose would be to print an Australian English language version of BYTE. Thus began a series of long distance negotiations, proposals, Telex messages and phone calls concerning the arrangements. Now that all the negotiating and arrangements have been crystalized into a signed contract, we can announce what has transpired.

Beginning with the January 1977 issue of BYTE magazine, two new editions will be published for readers in the more technologically sophisticated areas of Southeast Asia. One edition, in English, will be printed and distributed to subscribers in Australia, New Zealand, Singapore, Hong Kong, the Philippines and other countries where readers of English are interested. A second Asian edition will be translated into Japanese and distributed in Japan. The editorial content of both new editions will be identical (English edition) or identical semantically if different in detail (Japanese edition). For the first issues, the advertising copy will also be identical; but John's office in Sydney and his agent in Tokyo will solicit local advertising for these editions, while preserving the option for our US advertisers to reach these foreign markets.

Technologically, the arrangement is fairly

A BYTE family portrait, circa December 1976, Clockwise from top left are Manfred Peschke, Virginia Peschke, John Bannister and Carl Helmers. (Note: the reader probably suspects that ail those impressive looking books in the background are the world's greatest collection of computer tomes. While they do indeed look impressive, they 'd really only impress a farmer since they contain the genealogical records and trivia of the Guernsey cow breed.)

62

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You get both RAM and PROM memory, parallel, serial, cassette and video display interfaces, and software. Software includes a 512 byte bootstrap loader program so you can load any Processor Technology CUTS ("Byte/Kansas City") 1200 BAUD cassette tapes. Standardized subroutines in ROM, similar to those in a Sol personality module, are used by many Processor Technology software packages to improve program efficiency. You'll find you rarely need to touch your front panel switches. With our Subsystem 4ET you are up and running as soon as you turn on the power.

Three subsystems are available, depending on your memory requirements. Each Subsystem "B" includes five S-100 bus compatible modules as listed below. Each is dependent upon our new GPM module (GPM = General Purpose Memory) which provides 1024 bytes of low power static RAM and 512 bytes of preprogrammed EPROM as well as space for up to 8192 bytes more of ROM or 2708 type EPROM. The GPM module accepts the new ROM version of our well known ALS-8 Editor/Assembler software package.

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John Bannister (left) and Carl Helmers discussing the problems of translating B YTE into Japanese, white perusing the Japanese edition of Scientific American, December J 9 76. It turns out that translators do some interesting things. For example, in the translated version of an article by an author with a name of, for example, "Lane," the initials stay in Roman characters, but the surname — since it has a generic equivalent in Japanese script — is translated. But if the surname has no immediately identifiable generic root or equivalent, it remains in English spelling as do technical terms with no direct equivalent.

simple. At the time we give the final OK to the negatives from which BYTE is printed each month, our printer, The George Banta Company of Menasha Wl, will make duplicate copies of all the negatives, and send them to Sydney where John will modify the book to fit the local edition. Eventually this will include local advertising, local club and newsletter information, and possibly putting in new product information and related items of interest to local readers. The bulk of the material in the magazine will, however, remain identical to the US edition.

All our Australian, Japanese and Asian subscribers will be given the option of converting their subscriptions to the local edition which, due to its simultaneous publication, will be up to date as opposed to three months behind due to shipping delay.

Once it became apparent that we would be able to get together on this venture, John made the trip from Sydney to Peterborough NH via Lost Angeles. I call it Lost Angeles because the airline on which he was traveling managed to lose his luggage in the transfer. Arriving at Logan Airport, Boston (after neglecting to tell anybody what flight he was coming on), he was met by Debra "Sherlock" Boudrieau of BYTE, who in a feat of deductive reasoning and investigation, managed to pinpoint the flight and John Bannister, using only his one statement, "I'll be there at 8:30 tomorrow morning." As recounted later, it was a simple deduction: There was only one transcontinental flight

out of Los Angeles which arrived at Logan at 8:30 AM, and an Australian newly arrived is easy to spot: After an elapsed travel time of 22 hours with essentially no sleep, watch for the only person who is walking in a daze.

After initial greetings on arrival in Peterborough, John sacked out for about 15 hours, after which we began an intensive series of conferences on the details of publishing remotely, how to arrange shipment of the negatives, timing the monthly operation, etc. After a busy two days, I picked up John at midnight on December 1, and we spent the wee hours at my home and laboratory discussing things and comparing notes on the problems of computer enthusiasts in our respective countries. After I dropped him off back at the motel around 4 AM, we all showed up at the BYTE offices and took the pictures accompanying this editorial. Then, with the contract signed, Virginia and Manfred Peschke and John went to New York (by way of Boston) for a visit to Scientific American (see box) and some of the fabled surplus outlets which are reputed to still exist in that city. Manfred and Virginia finally saw John off to Australia from New York and returned to Peterborough that weekend.

One of the details of the Australian arrangement is a surprise and delight to Deborah Luhrs, who has been with BYTE nearly from the beginning. In order to assure a bit of experience, as far as handling subscriber orders and managing an office is

64

IF YOU'RE STILL PLAYING GAMES IT'S BECAUSE YOU HAVENT SEEN OUR SOFTWARE LIBRARY

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BOOKKEEPING

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Building

Compound

Cyclic

Decision 1

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Depreciation

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Interest

Investments

Mortgage

Optimize

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Pert Tree

Rate

Returnl

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Schedule 1

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Judy

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Nixon

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Part 3

MATH & ENGINEERING

Beam

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A Note of Thanks to Scientific American

We at BYTE wish to thank David Trusseil of Scientific American for taking time out of a busy schedule to meet with Virginia and Manfred Peschke and John Bannister of B YTE to discuss some of the probiems and pit fails of publishing foreign language editions of magazines. With the Japanese guage edition of BYTE we begin our such version in translation y and it proved quite helpful to us to have a bit of informal and friendly advice from people experienced in that endeavor.

We also learned that Scientific American, which is printed on extremely high quality paper, has lately been having trouble procuring supplies. The paper is necessary to achieve good reproduction of the color images which are so characteristic of their product. Who could possibly be eating up all the good quality paper? It turns out that there is a hot competition between Scientific American, Oui and Penthouse to see who can buy all the special paper. This quality magazine is being skinned alive!

concerned, John thought it a good idea to take up a suggestion which Virginia made: that Debbie should travel to Australia for a few months to help set up the office of the new firm, BYTE Publications [Austr/JapanJ Pty Ltd. Although Debbie left today (December 6 1976) as this editorial is being written, she still doesn't quite believe that it's all really happening!

Who is John Bannister, our new "Affiliate Publisher Southeast Asian Editions"?

John is a man of considerable experience in the Australian electronics industry, in the Sydney area. He became interested in small scale data processing systems following Don Lancaster's original TV typewriter articles in Radio Electronics and the later articles by Jonathan Titus and company on the"Mark-8 processor in that same publication. His assistant in business operations (bookkeeping and moral support department) is his wife Pamela, and he's well aware of the possibilities for using personal computers in the education of his two preschool age children. He's convinced (as are we) that it is just a matter of time until the revolution of personal computing we've seen in this country finally reaches his own country and Japan — to say nothing of the other technologically oriented countries of the world."

WHO NEEDS IT?

Biphase cassette recorder interface, digital comparator, no adjustments, switch - selectable speeds. Altair, IMSAI, Tarbell compatible. Manual $2.50 Kit $120.00. Assembled $160.00.

NEW

Universal cassette interface with independent latched input port for keyboard or other use, interrupt capabilities, switch-selectable baud rates, 800 to over 10,000 baud, digital comparator, level and sync indicators, status ports, extra IC pads for recorder relay. User selectable sync character. Altair, IMSAI, Tarbell, Kansas City. Manual $3.50 Kit $135.00. Assembled $180.00. C.O.D. $1.50.

DAJEN Electronics

7214 Springleaf Ct. Citrus Heights, CA 95610 (916) 723-1050

Z-80 COMPUTER

SYSTEM with RAM/PROM Module Cabinet & Expansion P/C Backplane Controls and Power Supplies Manuals - I/O Options, Kit CQQK

ALTAIR/IMSAI/P0LY/S0L

Compatible Modules

Z-80 Processor Board $150.

8080/6800 CPU Board 130.

8080ACPU& RAM/PROM 210.

Memory Modules 4/8/16/32K RAM from 100.

2/4/8/16K PROM from 90.

1-0/Communications mod. 95.

Video Display Module 180.

3M Cartridge & I nterface 290.

Floppy Disc & Interface 690.

DEC LSI-11/4K Module 800.

COMPUTER SYSTEMS

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St. Clair Shores, Mich. 48081

WHEN YOU NEED

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SPECIFY: N0K0R0DE "RC." SOLDER

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66

MORE HIIESON MAGIC!!!

Now ... the already tremendous value of MERLIN, the best, most versatile video interface, is an even greater value with the introduction of two inexpensive add-on features.

SUPER DENSE GRAPHICS

$39.00

320H X 200V RESOLUTION

MERLIN'S Super Dense Graphics is an add-on board which mounts directly to the MERLIN Video Interface. Each of 64,000 graphic dots is individually controllable and located on-screen. The kit includes a manual with X-Y coordinate transformation software listing.

SOFTWARE CASSETTE I/O

$29.00

1500 BAUD

MERLIN'S Software 1500 Baud Cassette I/O is an external add-on to the MERLIN Video Interface. It connects, along with a keyboard, to the MERLIN KYBD and I/O Port through a 16 conductor flat cable. The kit includes a manual with a listing of all necessary software, also available as part of the MEI ROM.

For more information, fast, write us direct.

Pricing:

MERLIN Assm. $349.00

MBI ROM/RAM $ 39.95

Super Dense Add-on $ 39.00

MERLIN Manual ....

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Master Charge and BankAmericard accepted.

MimTerm Associates, inc.

San Francisco Bay Area - Where It All Started - Has Its First Home Computing Convention

7,000 to 10,000 People

100 Conference Presentations

200 Commercial & Homebrew Exhibits

Two Banquets with Outstanding Speakers

Special-Interest Social Centers

Publication of Proceedings Being Planned

In Northern California's Largest Convention Facility, San Francisco's Civic Auditorium

CONFERENCE SECTIONS ON HOME COMPUTING

Being Plan

• Computer Graphics on Home Computers •

• Computer-Driven & Computer-Assisted Music Systems •

• Speech Synthesis Using Home Computers •

• Computers & Amateur Radio •

• Computer Games: Alphanumeric & Graphic •

• Personal Computers for the Physically Handicapped •

• Computers & Systems for Small Businesses •

• Tutorials for Hardware Novices & Software Novices

Software Design for Personal Computers Micro programmable Microprocessors for Hobbyists Optical Scanning for Inexpensive Program & Data Input Floppy Disc Systems for Home Computers Hardware & Software Standards for Personal Systems Seminars for Club Leaders, Editors, Organizers, etc. Personal Computers in Education (associated with a University of California short-course)

AND MUCH MORE

PRESENT-WORLD & FUTURE-WORLD BANQUET SPEAKERS

Banquets to be Held in Fascinating Speakers will

• Frederik Pohl, Science Fiction Writer;

Lecturer to NASA, American Astronautical Society, New York Academy of Sciences, World Future Society, etc. Robots You Can Make for Fun & Profit

• John Whitney, Pioneer Computer Film Maker,

Computer graphics experimenter under grants from NEA, Guggenheim Foundation, & IBM

Digital Pyrotechnics: The Computer in Visual Arts

San Francisco's St. Francis Hotel Discuss the Past, Present, & Future

• Henry Tropp, Mathematician, and Principal

Investigator for History of Computers Project jointly sponsored by the Smithsonian Institution & AFIPS TPie 1940's: The FIRST Personal Computing

• Ted Nelson, Author & Fantast, Director of

Xanadu Electronic Literary Network, Lecturer at Swarthmore College

Those Unforgettable Next Two Years

Era the

tprll lg-17, 10*7*7 • Ban francisco

©77-1-12a by Computer Faire

68

MICROCOMPI

^Cut out, or photocopy; then fold, and tape in position.

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Jfg, **<>■-*%«? <^

»*M,

***».

FIND OUT ALL THE DETAILS

GET YOUR FREE COPY

OF THE

SILICON GULCH GAZETTE

• Details of the programs & speakers

• Information about the banquets' arrangements

• Accommodations information, & registration forms

for the St Francis Hotel (Faire Headquarters Hotel), & the other three Computer Faire hotels

• Pre-registration details for the Faire

(reduced admission for those who pre-register) Details of the Proceedings expected to be published Articles about the homebrew exhibits Weather information, & tourist trivia regarding

San Francisco Listings of the commercial exhibitors AND, just to make it interesting:

— "Hot news'' & raging rumors from "Silicon Valley"

(the San Francisco Bay Area)

— Product announcements, equipment descriptions,

hardware & software news, etc.

CO-SPONSORS INCLUDE AMATEUR,

PROFESSIONAL, & EDUCATIONAL GROUPS

• The two largest amateur computer groups:

Homebrew Computer Club

Southern California Computer Society (SCCS)

• Both Bay Area Chapters of the Association for Computing Machinery (ACM)

San Francisco Peninsula Chapter Golden Gate Chapter

• IEEE Computer Society's Santa Clara Valley Chapter

• California Mathematics Council

• Stanford University's Electrical Engineering Dept.

• University of California's Lawrence Hall of Science

• People's Computer Company (PCC)

• Community Computer Center

• Bay Area Microcomputer Users Group (BAMUG)

• Professional & Technical Consultants Assn (PATCA)

• Amateur Research Center

april XS-ITT, 1977 • san franciscoj

©77-1-12 by Computer Faire*

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69

Simplified Omega

Ralph W Burhans

Research Engineer and Lecturer

Ohio University

Electrical Engineering Dept

Athens OH 45701

Photo 1: Mini-0 microcomputer interface, with the radio frequency front end. The RF front end (in the foreground) is essentially a receiver for 10 kHz radio signals broadcast by Omega transmitters widely spaced around our planet. The device was built in prototype form using perforated board and sockets, as seen here. The microcomputer interface (to a JOLT system) is via the mounted plug at the right of the interface box (rear unit in photograph).

TO FRONT END (FIG 2)

Antennas

The receiver is designed to use an E-field short whip or wire antenna of random length. This type of antenna is often called an "E-field" antenna because it responds to the electric field component of the radio signal. A 20 cm wire will do in many cases if the antenna is mounted in the clear. A 10 meter length wire works well in cases where there is not a lot of local 60 Hz harmonic interference. Unfortunately, the Omega System's 10.2 kHz is exactly the 170th harmonic of 60 Hz and urban laboratory monitors sometimes have problems with bursts of 60 Hz interference from high power SCR-TRIAC controls or rotating electrical machinery. The boat owner or aviation buff usually doesn't have problems with AC line interference and a short whip mounted vertically will often suffice for the antenna.

Preamplifier

The preamplifier of figure 1 is constructed in a small weatherproof box with a tight feedthrough insulator or fitting right at the antenna and a coaxial cable lead-in for the signal back to the receiver (see photo 1). The coax supplies both power to the preamp and a preamplified Omega signal back to the front end module. The circuit is not critical but should be adjusted for a broadband peak at about 10.2 kHz by minor changes in the 0.02 pf capacitor across the inductor. Tapping down on the 600 ohm line output transformer improves the Q of this simple bandpass filter circuit.

Figure I: Mini-0 antenna preamplifier, 10.2 kHz. This preamplifier is shown as constructed in one version in photo 4. The 2N5I39 transistor must be selected for a high ]3. Power for this preamp is sent up the coaxial cable from the front end unit, thus sharing the same wire with the signal. The transformer, T, is a 600 ohm center tapped to 600 ohm center tapped line to line transformer, a Mouser 80TM0I6 or 80TM009 part number in electronics catalogs. The Q factor for this amplifier is 2, with a gain of 20 dB at 10.2 kHz.

70

Receiver Details

ping down on the 600 ohm line output transformer improves the Q of this simple bandpass filter circuit.

The preamplifier has an input impedance of 1 megohm with a 1 k ohm series resistor as a current limiter for gross interference such as from nearby lightning discharges. We have yet to burn out a 2N3819 JFET in these front ends but have had trouble with similar MOSFET input transistors in earlier preamplifier systems. Other JFETs like the M PF102 will work just as well.

The 2N5139 PNP transistor provides a gain of 20 dB or so in this circuit and the transistor should be selected for a high beta, greater than 100 if possible. The Q of this circuit is about 2 which supplies some desirable reduction of low frequency and high frequency interference in the very first stages of the receiver.

Front End

The heart of the radio frequency analog circuitry involves a multistage bandpass filter with two active filters and two passive mechanical filters, as in figure 2. The signal from the preamplifier drives the first Seiko SM-31 R mechanical filter directly from the

Omega Navigation is a method of determining where your boat or plane is currently located, anywhere on the globe. It is a "free" method of navigation to a certain extent; since it is sent out by the cooperating nations via radio transmissions for shipping and defense traffic, but is available to any technological hitchhiker willing and able to build the proper interface. (Free in this instance is defined to mean the accounting for each person's share of the tax cost is so diffuse it can't be traced.)

In this month's installment, Ralph W Burhans continues the Omega information with the description of the detailed function and circuitry of an Omega navigation receiver which can play with any microprocessor system possessing an 8 bit input port [The Mini-0 Omega receiver design is intended for an experienced amateur electronics person, and to the best, of our knowledge is not yet available in kit form for the novice.] How do you use it once it's built? The details of the software will have to wait until the third and final part of this series, by Richard ] Salter, which will appear in the next BYTE.

■■■■■■

680 ohm isolating resistor which supplies power to the preamplifier. This first stage of mechanical passive filtering is followed by an active tunable bandpass filter to help reduce sideband responses and increase the system gain. A 1 k ohm pot at the output of this first active filter is used as a radio frequency gain control. The next stage is quite similar.

FROM

PREAMPLIFIER @(FIGI) J

.002

.01

LM324 QUAD OP AMPS 500

.01

^

6.8K —'WV—

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► 680

4

SEIKO SM-B

47K

RF GAI

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r

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I0K

IN9I4 DIODE BRIDGE LIMITER

i

^>

i

V/2 BUS

■H>

OUTPUT K TO ZERO

CROSSING

DETECTOR

Figure 2: Mini-0 mechanical filter front end amplifiers. This active circuit uses two mechanical filters manufactured by Seiko to provide a narrow bandwidth of 14 Hz at the -3 dB points and a gain of 40 to 60 dB. The output passes through a diode bridge limiter implemented with an operational amplifier section, prior to reaching the zero crossing detector of figure 3. The physical construction of this circuit is shown in photo 3.

71

Photo 2: Mini-O in operation on the bench. The setup shown here uses a Teietype Model 33 ASR with the JOLT computer (at right in front of power supply), and the Sinclair clock reference (in front of interface box on bench). The display on the oscilloscope shows output from a lines of position digital to analog conversion output described (in concept) in part J of this article.

The Seiko filters are available from:

Seiko Instruments Inc 2990 W Lomita Blvd Torrance CA 90505 Phone (213) 530-3400

Seiko also has filters for the 11.333 and 13.600 kHz Omega channels; write for information. The original SM-B filter has now been changed to type SM-31 R.

Order a SM-31 R 10.200 kHz 2 piece kit: unit cost $8.50 X 2 pes = $17, postage and handling charge = $1.50 [6% sales tax for California Residents only].

We have found that it is usually necessary to provide the 1 k load resistors to ground at the output of each of the operational amplifier stages as shown, to help reduce regeneration problems [ie: oscillations neither planned or desired | which depend on the particular parts layout on the circuit board.

The overall system gain and frequency response can be altered by changing the 6.8 k ohm feedback resistors across the first two op amps to 15 k ohms or so. However, too much gain here results in instability. The overall gain of this filter and limiter circuit is about 40 dB as shown. The bandwidth is about 14 Hz at the -3 dB points and the skirt selectivity is excellent, about -80 dB down at the next Omega channel frequency of 11.33 kHz!

Several other types of front end bandpass filter arrangements have been used with Vernitron ceramic filters and with Statek quartz tuning fork filters. However, these are more difficult to fabricate and adjust properly or involve more expensive circuitry compared to that required for the Seiko SM-31 R mechanical filters.

Alignment of the filter of figure 2 is quite simple. A stable function generator with a sine wave output at 10.200 kHz is fed to the input terminal through an isolating capacitor

and attenuator. The output from the limiter stage is observed on an oscilloscope and tuned for a peak amplitude by adjusting both 500 ohm trimmer resistors on the bandpass stages. It might be desirable to check the impedance matching by altering the 0.002 jjlF input capacitors from each SM-31 R filter. These serve to "tune" the filter peak to about 10.200 kHz but are rather broad. A capacitance between 0.002 and 0.003 mF is usually required and a fixed ceramic type capacitor is adequate or perhaps two parallel ceramic capacitors to adjust each filter peak to 10.200 kHz (such as 0.002 in parallel with 0.0005). In tuning the filter circuit be sure to attenuate the signal generator to a low level so that the limiter is not clipping the peaks at the output. The operation of the limiter can be checked by increasing the drive to the filter to the point where the output starts to look like a square wave with rounded-off corners. The limiter peak-to-peak threshold is about 1 V using 1N914 diodes. Other types of limiter circuits using the MC1357 or LM2111 IC chips have also been used but the simple diode bridge circuit of figure 2 is adequate for most Omega users. If you happen to have a dual channel oscilloscope, the phase shift versus signal amplitude may

72

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Photo 3: Mechanical filter front end board. This picture details the construction of the mechanical filter front end for the Mini-O receiver, described by the circuit diagram of figure 2. The potentiometer hanging loose at the left is the I k RF gain potentiometer, R1 in figure 2 The board shown here also includes the zero crossing detector of figure 3y at the right.

be checked by observing the input signal on one channel and using this to synchronize the scope sweep while observing the filter output on the other channel. There should be very little shift of the phase as the signal level is increased up to the point of limiting. At the limiter threshold only a slight phase shift should be observed. If a large change in the phase when limiting is observed, it usually means the circuit layout is poor and some kind of regeneration is taking place, or undesirable feedback; extra bypassing of the V/2 power bus with a tantalum low inductance capacitor of 10juF might help, or reduce the overall circuit gain by changing the active filter feedback resistors to a lower value.

Zero Crossing Comparator and Envelope Gate Generator

The output of the limiter of figure 2 drives the comparator circuit of figure 3. The 10.2 kHz zero crossings are obtained from one section of a quad LM339 comparator integrated circuit. This circuit is designed with a small amount of hysteresis and is intended to be centered on the V/2 output level of the limiter stage output DC level. LM339s are not perfect and usually have a slight offset so that it is desirable to trim the exact operating point by summing a

very small correction from a resistor returned to the positive power supply of +5 V. A value of 500 k ohms to 2 megohms is usually sufficient with 750 k shown in the

D- +^Y_ ADJUST FIXED R

iok ri^Tj F0R BEST THRES

(v/2 BUS) ^J^^J^J HOLD OFCOMPAR

I

IOOuF POWER PIN BY

* PASSING ON LM339

-o(l2)GND

INPUTS FROM

FRONT-END

(FIG2)

(ZERO CROSSINGS PER SECOND) (TO FIG 7)

QUAD LM339 COMPARATOR + 5V

J

AUTO START {AS> GATE OUTPUT (TO FIG 4)

GATE THRESHOLD

ADJUST

SIGNAL LEVEL INDICATOR

Figure 3: Zero crossing detector. This circuit shows the LM339 comparator sections used to determine zero crossing transitions (A), monitor the current signal level (B) and generate the automatic starting gate output (C) based on current signal level. The zero crossings output threshold is set by resistor R2t which must be selected to give the best threshold response. The auto start output is an "envelope gate": It is high when the signal is above the threshold set by R3} and low when below that threshold.

73

AUTO-START GATE FROM FRONT-END

Oi

)

2l5(Hz) |

<d

ALTERNATE: SINCLAIR RADIONICS

"BLACKWATCH" 215 Hz SOURCE (SEE FIG 6)

-HO

C 4017 CA

R 2 7

0.8Hz)

3-P0SITI0N SLIDE SWITCH

ROI 234567

!25mS STROBES FOR MEASUREMENT WINDOW FLIP FLOP (FIG7)

LED STATION INDICATORS

h-.|Hz CYCLE (10 SEC)

DM8865 LED

DRIVER

I I I I

Figure 4: Housekeeping timer circuit (HKT). The housekeeping timer is used to generate ail the signais needed by the interface. A crystal osciliator is shown with a 2** Hz (32.768 kHz) frequency, with wiring indicated for use of the Sinclair Radionics "Biackwatch " wristwatch as an alternative source of the signal. (If the watch is used, omit the crystal oscillator.) A three position slide switch is used to control operation modes, which include automatic start, manual starting or a clear operation. The LED display driver outputs of the DM8865 provide a continuous monitor of the Omega cycle, and the A slot is monitored by the interface to the computer to give software a timing reference to stations.

diagram of figure 3. The idea here is to adjust the comparator such that it will provide a square wave output with as low as 10 mV peak-to-peak input centered on about V/2. This threshold will correspond to about 10juV peak-to-peak at the antenna terminal (about 3 \±V rms) which is usually well below the antenna noise level when the gain ahead of the comparator is about 60 dB. The front end gain will be about 20 dB for the preamplifier plus a minimum of 40 dB for the filter and li miter which provides 60 dB total. More gain can be provided if required by changing the amplifier feedback resistors on the active filters as mentioned previously. Thus the zero crossing comparator should provide an output square wave for essentially all signals and noise when the antenna is connected to the preamplifier. The output of the comparator is a hard limited square wave, but the filter-limiter circuit has what is known in the trade as a clipped linear characteristic. The edge position of the comparator square wave contains the basic phase information of the Omega signal plus the noise developed at the antenna within the filter bandwidth used.

The other sections of the comparator are used to provide an envelope output signal

TT

H A

TT

<±y

"A" TIME SLOT SELECT (TO FIG 7)

I W\r4

47K

+ 5V

J

with a peak detector and an adjustable threshold gating circuit. The peak detector drives a signal level indicator which is handy for observing strong signals like the North American D channel on 10.2 kHz, as well as the overall receiver noise level. The meter should kick upscale slightly when the antenna is connected even in a very electrically quiet environment. The typical noise level in the 10 kHz region will vary from 10juV to 100/iV per meter of antenna length (assuming a perfect energy transfer at the antenna) for a receiver bandwidth of 15 Hz or so. The Omega signals will vary from a low of about IOjuV to a high of 1000^V depending on the range of the observer to the Omega transmitter. The noise level during local thundershowers can be much greater than the signal, and 60 Hz harmonic interference can often completely obliterate Omega signals as observed on a scope attached to the radio frequency front end. However, the digital1 processors which follow the zero crossing edge output can track signals buried in a large amount of noise with proper programming. [Software is the touchstone of computer applications.]

The adjustable threshold gate is used as an automatic start signal for operating the housekeeping timer (HKT) circuitry. We usually also connect an LED from +5 V through a 330 ohm series resistor directly to this gate output point to indicate when the strong D channel is on. An audio beeper

74

circuit connected at this point is also a handy device when first starting to observe Omega signals. This amplitude gate output is zero when on, so it operates as a current sink when driving external digital interface hardware. We have found that this circuit will start the digital logic operating 95% of the time or more, even in the presence of a lot of noise because the D channel Omega signal is quite strong for most observers in North America. For others, a manual start option is provided in the housekeeping timer circuit, and for the very sophisticated user, an automatic synchronization routine can be developed using the microprocessor with appropriate software.

Housekeeping Timer and Local Clock Oscillator

In order to operate an Omega receiver it is necessary to have some sort of timer circuitry and reference clock oscillator. The timer provides a means of telling the receiver which stations are being received, and the clock provides a reference for comparing the phase differences among stations. The clock oscillator drives the timer circuitry through an appropriate series of divider stages. A very simple housekeeping timer circuit based on a clock frequency of 2'1* Hz is shown in figure 4.

A 32.768 kHz quartz crystal of the type found in digital wristwatches is used. The timer circuitry here provides a number of very convenient gating and control signals for operating external microprocessors or hardware digital sensor systems. The timer is started with a master reset gate (MR) obtained from the front end automatic start output or from a manual pushbutton. A set-reset flip flop holds the timer on as long as the receiver is operating. The timer can be reset by switching to the stop position (or clear) and momentarily operating the same

control pushbutton. The housekeeping timer tells the receiver user where the Omega sequence is with LED indicators. For a microprocessor interface only one of the stations need be selected to identify where the Omega sequence is, such as starting at the A or D channels. Beginnners might find that a string of eight LEDs, one for each time slot, is a value in understanding the operation of the Omega sequence.

A uniform measurement window method has been used in this housekeeping timer circuit. If the clock is started at the beginning of the D Omega time slot, then the sequence of gates is as shown in figure 5. A measurement window for each Omega time slot is obtained with additional clear, stop, and read gates for each one. The measurement window width can be altered by starting on pulse 1 and stopping on 8 instead of 2 and 7 as shown in figure 4. The goal here is to provide an easy way of telling the microprocessor when the measurement is valid. The HKT generates eight time slots every 10 seconds with 10 shorter 125 ms control gates for each one under the option of whatever the user desires to program.

Clock Adjustments

The 32.768 kHz clock should be adjusted for an offset of 5X10_6 or less. A reasonably good frequency counter with a built-in 1 MHz temperature compensated crystal oscillator time base can be used. First adjust the trimming capacitor on the clock oscillator to read 32.768 with a 1 second counter gate time. Then adjust for 32.7680 with a 10 second gate time. If a period averaging feature is available on the frequency counter, 10^ periods of the 32.768 frequency will result in a number like 30.51757 microseconds which gives a reading of ±3 parts in 10*7 precision with respect to the frequency counter time base crystal. If you

Photo 4: The RFpreamplifier, shown built with a homebrew printed circuit board and mounted in a shielded metal housing. The antenna is mounted at the left, with the connection to the receiver front end box via coaxial cable at the right.

75

AUTO START

NO SIGNAL GAP, 0.2 s

J

J°l'hhl-I'l-H'l*l_ n

R

W//////A.

A0.9s

1.0s |

Figure 5: Timing diagram, showing how the iogic of figures 4 and 7 combine to produce a hardware defined measuremen t windo w which wiii vaiidiy sample a segment of the signal from each station. The diagram assumes that the automatic start begins on the leading edge of the signal from the D station. The portion of the transmission interval between dotted lines in the E} F, G, H, A, B and C station signals is monitored by the Mini-0 software through the interface.

UNIFORM l.25s TIME SLOT WITH TEN , 125ms GATES

START (BEGIN WINDOW)

STOP (END WINDOW)

MEASUREMENT WINDOW

M

READ OR WRITE

1_

TRANSMITTING TIME POSITION OF OTHER STATIONS RELATIVE TO AUTO START ON D WITH UNIFORM MEASUREMENT WINDOW

1_

do not have a frequency counter, the nearest CB repair shop usually does, and the clock may be carried to the frequency counter location for initial adjustment. Once adjusted the clock may be operated in the on-off mode with occasional checks using the Omega signal to estimate the offset for periodic recalibration.

Commercial and military Omega receivers often use a temperature compensated crystal oscillator clock on a frequency like 2.611200 MHz (2$ X 10.200 kHz). Suitable divider chains can be easily assembled to generate all of the Omega time slot functions from this particular frequency. It is also possible to devise frequency synthesizer circuits based on 5 MHz standards and some receivers have an atomic clock reference for use in the direct ranging mode. The 2^5 Hz watch crystal oscillator provides adequate stability when treated with some care and is many orders of magnitude less expensive than other methods.

isolating high impedance buffer amplifier. A circuit to modify the Sinclair watch kit is shown in figure 6. The output of this circuit is used to drive the oscillator of figure 4 by removing the crystal from the circuit of figure 4 and driving between ground and the input side of the oscillator gate right across the frequency trim capacitor. The GT-500 clock requires an additional 4024 divider stage to generate 2^5 Hz from the crystal frequency of 2^1 Hz.

Marine navigator types might find that a clock such as the Sinclair Blackwatch which has a digital display for time of day in hours-minutes, or minutes-seconds, is of value also as a celestial navigation chronometer. Once the clock has been properly adjusted, the user can even estimate when the D channel should be operating by keeping track of the clock offset on a daily basis using the seconds readout. The Sinclair watch kit can provide better than 1 second per week offset with respect to Omega. Thus the receiver user can also start the receiver manually by operating the pushbutton when the estimated D channel second interval is displayed on the clock readout. The gating system of figure 5 with uniform time slots is designed such that errors up to a quarter of a second can be tolerated and still provide some measurement window. The automatic starting gate will start using the strong D channel within 50 ms of the correct station spacing illustrated in figure 5, and manual push to start operation can be achieved within 100 ms with some practice in "clock watching."

Microprocessor Interface

The next step in the receiver operation involves converting the 10.2 kHz Omega zero crossings to a sampled set of 6 bit numbers. First a single chip rate multiplier, an RCA CD4089BE, multiplies the 32.768 kHz frequency by 5/16 to generate 10240zps (zero crossings per second) clock rate. There will be some jitter at the LSB rate but this will wash out in the processor which needs only six of the eight bits for Omega use.

The Omega zero crossings are fed to a digital mixer circuit consisting of one D flip flop (144013) and mixed with 2^1 Hz obtained from the housekeeping timer circuit of figure 4. The mixing formula here is:

IF= f- (m+1) 2n

Other 215 Hz Clocks

A Sinclair Blackwatch or the Westclock GT-500 wall clock movement have been used to provide the 2»* Hz signal with an

where:

IF is the intermediate frequency in Hz,

f is the input frequency,

m is the harmonic number of 2n Hz

76

which is nearest and lower than the input

frequency,

n is an integer.

The result for Omega is IF = 40 Hz when 2" a 2048 Hz and m = 4. We have now converted the Omega 10.2 kHz signal to a 40 Hz signal using simple digital mixing where the phase of the edges of the 40 Hz track the Omega phase within 2048/40 or within 51.2 parts per cycle. This is a convenient number in that 5 X 51.2 = 2°. A 6 bit number (1 part in 64) can specify the Omega phase but the precision of measurement will only be 1 part in 51.2 of the actual Omega phase. This is more than adequate for simple Omega receivers which typically have errors of ±1 nautical mile, and 8 miles represents an Omega lane. In effect the binary system generates phase to within 2/100ths of an Omega cycle or lane as applied to distance measurement over the earth surface. It is also worth noting here that the phase direction of the 40 Hz signal changes opposite to that of the Omega signal, that is, the effective LO is on the high side of the Omega signal or 10240 Hz is above 10200 Hz by 40 Hz. This is of no consequence since the subtraction to obtain the correct line of position direction can be reversed using complementary arithmetic.

The 40 Hz output signal from the mixer is inherently noisy and also contains higher harmonics of the LO. A binary phase lock loop (BPLL) consisting of the 4030-4011 and 4040 CMOS chips of figure 7, provides nine bits of filtering and a clean 40 Hz signal. The phase data contained in the 40 Hz edges may actually be used at this point without any microprocessor by starting an RS flip flop with an 8 Hz edge obtained from the housekeeping timer and stopping with the next 40 Hz edge. The width of the resulting on-off pulse is directly proportional to the phase of the original 10.2 kHz Omega signal with respect to the local clock which generates the 8 Hz reference. A suitable counter, averaging, and subtraction circuit can be devised in hardware to measure Omega lines of position where the filtering time constant will be the width of the gating interval of figure 5, or about 8 Hz/5 for a bandwidth of 2 Hz.

For microprocessor use we sample the cycling 40 Hz clock obtained from the rate multiplier and 8 stage counter of figure 7, with the 40 Hz Omega signal from the binary phase lock loop filter. An 8 bit three state latch (4508) stores the individual Omega phase readings as 6 bit data and the other two bits of the latch are used to store the station status information from the gating circuitry of figure 7. These 8 bit

Integrated Circuits for VLF-LF Receivers

In our VLF-LF navigation lab at Ohio University we have found a great many standard IC chips useful for Omega (10 kHz range) or Loran-C (100 kHz range) receivers. Experimenters skilled in the art of fabricating high gain receiver circuitry might wish to substitute various other circuits for the Mini-O front end system. The following list of ICs has been used with both Omega and Loran-C systems:

AM Receiver Chips (identical circuits) Fairchild uA720 National LM1820

RCA CA3123

Signetics N546

AM-FM-SSB Receiver Chips (not identical circuits)

Fairchild uA721 National LM373 or LM374 Plessey SL1624C

RCA CA3089

FM Limiter Detector Chips (used as envelope detectors

by feeding input to limiter, also to quadrature input) Fairchild uA721 Signetics ULN2111 National LM2111 RCA CA2111

identical types

FM Limiter Amplifiers (not identical circuits)

Signetics ULN2208 Signetics ULN2209 National LM703 National LM371 National LM370 (AGC type) Fairchild uA757 (AGC type) RCA CA3028

RCA CA3053

There are probably others which would be suitable; refer to the manufacturer's literature and application notes. One of the newest types, the Fairchild uA721, appears to work for both Loran-C and Omega receivers and has the potential for providing a noise blanker using the mixer stage, without adding any additional active circuitry to the front end.

ADDED BUFFER CIRCUIT

Figure 6: Use of the Sinclair "Blackwatch" wristwatch kit as a source of the 2?$ Hz reference signal (32. 768 kHz). This circuit was used by the author to provide both chronometer functions and Omega reference timing by mounting it in a plastic case so that the L EDs could be seen (see photo 2).

2'5 Hz ALTERNATE REFERENCE CLOCK SOURCE (TO FIG 4)

TO

SEGMENTS OF WATCH { DISPLAY

O

b —

C — d e —

f —

g

— Dl D2

— D3

— D4

m

. TO DIGITS

)OF WATCH

DISPLAY

J

CAUTION:

SOME MODELS MAY HAVE SLIGHTLY DIFFERENT PlNOUT NUMBERING

^■IC NO, I IN SINCLAIR "BLACKWATCH" KIT

77

MIXER

BINARY PHASE LOCK LOOP

10.2 ZX INPUT (FIG 3)

INTERRUPT TO NMI-OR IRQ

REFERENCE COUNTERS

-£>

OSELECT FROM PROCESSOR ADDRESS DECODER, FlG8

8 BIT

DATA BUS TO

PROCESSOR

D6 ON FOR A ONLY D7 ON FOR 625 ms OF EACH TIME SLOT

"A" TIME SLOT {FIG 4)

4013

MEASUREMENT WINDOW FLIP FLOP

Figure 7: 8 bit processor interface. This is the interface used with the JOLT or KIM-1 versions of an MOS Technology 6502 in the author's laboratory. The address se feet ion logic is shown in figure 8. The mixer and phase iock ioop generate a 40 Hz difference frequency which drives the processor's interrupt line. This signal also provides the latching signal to the 4508 bus interface, so that when the processor responds to the interrupt it will have the data which was current at the time of the interrupt. The binary rate multiplier (4089) is used to divide the reference frequency to provide a crystal controlled clock into the reference counters, so that the count of crystal controlled cycles can be read following the interrupt.

numbers now become the raw Omega data for processing and status using interrupt requests to the microprocessor at every 40 Hz positive going edge. The data is used as if it were high order memory address with a decoder from the microprocessor address lines and output to the 8 bit data bus with appropriate software, figure 8. There are other ways of implementing the interface with about the same hardware depending on the particular microprocessor system used. If the 625 ms sample window of figure 5 is used, then there are 25 Omega phase readings valid for each time slot. That is, there will be 25 cycles of the 40 Hz signal in

625 ms. The microprocessor software designer can manipulate this data in various ways. Some receivers first estimate a mean or mode value. Many Omega processing systems create a software tracking loop which is similar in principle to a phase locked tracking loop as used in analog circuits. This can be done in the 40 Hz case by programming in increment-decrement addition to the 40 Hz interrupt edge position such that the new calculated position will tend to be exactly at the same phase value for each reading. This estimate is stored in memory for each time slot creating what we would call a software memory aided phase locked tracking loop. The loop output becomes the phase of each time slot with respect to the cycling 40 Hz reference clock and is subtracted in pairs to generate lines of position.

A microprocessor can be programmed to do this with 100 or so instructions. An equivalent hardware memory aided phase locked loop and lines of position subtraction would require at least 20 additional integrated circuits as well as a memory. Thus the

78

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Figure 8: Partial address decoder. In a small system} where only a portion of the total address space is actually used, it is possible to get away with partial decoding of addresses. This decoder lumps all addresses of the form hexadecimal 8xxx together as the (single) address for the Omega interface; for systems where memory address space utilization is a problem, other address decoding configurations should be used.

Acknowledgments

At Ohio University we have been developing low cost Omega navigation systems (ONS) for use by the general aviation community. The Mini-O system described here is a spinoff of some of the simpler ideas. Part of the work reported here has been supported by NASA Langley Research Center, Grant NGR 36-009-017, under the Tri-University Program in Air Transportation. The aid and support of Dr R H McFarland, Dr R W Lilley, Prof G E Smith, R J Salter, Lee Wright, Kent Chamberlin, Dan Moyer, and Ralph Smith are much appreciated on the project results.

TO

DISABLE OF 4508 LATCH (SEE FIG 7)

microprocessor can do this job as well as all the remaining computation to output some useful navigation information and still have space left for whatever the system designer wishes to do.

At this point we leave it up to the software designer to implement a navigation system on the microprocessor. We have supplied raw phase data at a suitable low data rate (40 Hz), a collection of Omega sequence and time signals for interrupt and control of microprocessor functions, and means of identification of where the Omega sequence is at a particular time. The first stage in programming involves developing sensor processor filtering of the data down to the lines of position level. The simplest marine receiver might require only two lines of position outputs. Further sophistication would involve conversion to latitude and longitude, range angle, diurnal corrections, multiple frequency redundant systems, differential corrections, etc. The next article in this series, by Richard Salter of our laboratory, presents some of the sensor software details.

Test Equipment Recommended

The Mini-0 receiver system is intended for fabrication by those skilled in modern electronic circuit arts. It is not recommended for the total novice. Access to some test equipment is required for alignment and checkout. An oscilloscope, preferably a triggered sweep model, a stable audio function generator, and a frequency counter with a quartz crystal time base, are suggested.

The function generator should be capable of tuning the range of 5 kHz to 20 kHz with some reasonable stability (with an internal regulated DC supply) and a tuning rate such that the frequency of 10.200 kHz may be set to within a few Hertz. The adjustment of the very narrowband front end requires setting the function generator to the center frequency of 10.200 kHz and this should be checked with the aid of a frequency counter operating in parallel or triggered from the function generator synchronizing output. We have used the EXAR model XR-2206KA kit

(available from James Electronics, POB 822, Belmont CA 94002, for about $18 as a basic chip plus circuit board). This provides a convenient squarewave output for checking frequency in parallel with the sine wave output. A good quality logarithmic tuning potentiometer is required in these types of function generators.

The frequency counter should have a 10 second time base with a quartz crystal reference that is accurate to within ±\X\Qr% or has a low offset. If you do not have this item, many radio amateurs often use them in their shacks, as well as CB repair shops. Some frequency counters have provision for using an external time base which can provide the required precision for initial adjustment of the 32.768 kHz clock oscillator. The Sinclair Blackwatch kit also has instructions for adjusting the offset using WWV time ticks on the high frequency (short wave) radio bands. This takes longer than using a good frequency counter but is adequate for the patient experimenter. For the experimenter who is involved with time and frequency measurements, a good 1 MHz secondary standard is suggested. Many oven controlled crystal oscillators are on the surplus market. (Herbach and Rademan, 401 E Erie Av, Philadelphia PA 19134, has several with proportional oven controls in the $30 to $50 price range; a reasonably priced temperature compensated crystal oscillator is available from Bliley Electric Co, 2545 W Grandview Blvd, Erie PA 16508, the model TCCO which requires 26 mA +5 VDC and costs about $75.)

Some experimenters might even wish to consider the possibility of using an external 1 MHz frequency standard as the microprocessor clock system so that all of the timing functions could be accomplished with precision using the microcomputer itself without ever using a special purpose Omega clock in the interface.

When using an oscilloscope, it is suggested that most measurements be made with a low capacitance probe so that the waveform displayed will not be distorted by the lead capacitance to the scope. When observing the input signal at the preamplifier output terminal or at the input to the front end, an ordinary coaxial lead to the scope may be used because the impedance at this point is about 680 ohms. However, the output of many of the CMOS logic circuits is a much higher impedance, and distortion of the actual waveform will take place unless a low capacitance probe is used. The CMOS logic circuits will tolerate up to something like 130pF additional capacitance, but this can distort a 1 MHz signal."

80

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Continued from page 13

attempting to sell the user the idea that the DEC PDP-8 that drove the readerwould fit in the palm of his hand in a few years. The Intel 8008 was just out, and those outside the integrated circuit world could not understand its potential.

In printers' terms the paper has a line screen of 25% density, similar to a printed photograph. All we did was to place the dots where we wanted them. To do this the RCA Vidiocomp was driven with our dot "font." The worst problem in producing the master was that the technicians adjusting the Vidiocomp did not really do a good job on the sweep linearity. It wasn't necessary in text, but it really came out in our reader. The data is encoded in a phase-like method where along the scan line the black dot is placed to either the right or left side of the cell, thus a black white or a white black. When scanned and converted to an analog signal, you have either a positive or negative transition at the cell center the same as many cassette tape recorders. This was done as we had just finished a cassette recorder design. The reader has a three cell scan head. Two cells track the line, and the third is the data cell. The organization is like a disk, where the first few lines at the beginning are a disk directory — in this case chapter paragraph line number starts. You can use the runout on each side to count your position the same as a disk head position encoder.

If anyone wants more information please contact me, C R Conkling Jr, at POB 310, Shoreham NY 11786, (516) 744-9475.

GRAY SCALE?

I am following your series of articles on the optical bar code readers with great interest. Basically I agree with Messrs Banks and Sanderson (December 1976 BYTE, page 12) that optical bar code readers and low cost printing will be "the way to fly." I would add that software would best be distributed as source code, although the technique could obviously be used for source or object code. I would suggest that the suggested format (figure 2, page 16) be enlarged to include a one byte "record type" code. This would allow for a far more flexible system at very small cost.

I borrowed my son's (inexpensive) microscope and gave the sample bar codes (figure 4, page 17) a close look. One thing became quickly apparent: Even on the low density sample a lens system of at least 200X was required! Any less and I could see more than one bar at a time. Secondly, holding the paper flat to prevent misfocusing was a problem. The high density samples had a problem obvious to the unaided eye — the ink smeared (see copy enclosed). My experiment indicated that your sample (e) was about the best. Sample (c) came close, but might present problems in tracking.

Several thoughts on the subject: Some form of audio feedback from the computer (have the processor make a "click" noise by toggling a one bit output port into a speaker) would help maintain the correct scan rate and tell when you had strayed off the track. Perhaps the bar code system is not the ultimate way to go; how about a "gray scale" — you could print white, 33% halftone, 66% halftone, and black (giving four levels) or what have you. The halftone system would allow printing of wider bars while yielding high bit density, thus reducing the requirements of the lens system. One final thought: With proper forethought, the bar code "pencil" could double as a "light pen."

Please keep up the good work, especially on this subject. I believe you are on to something very worthwhile.

Carl KZettner W5HFG

108 Moss Dr

San Antonio TX 78213

As noted earlier (see January BYTE, page I1) the smearing of the high density samples and variability of the spacing rule out their use. The actual problem can be attributed to a nonuniformity in the response of the photographic preparation of the plates for the print run, since the smearing was seen in our "blueprint" proof copy of December BYTE.

The magnification of the optics is not the problem; rather it is the aperture of the fens, and masking of that aperture so that only one bar width at a time is viewed. The sfit method (see comments in another section of this forum) shows good promise as an inexpensive but quite usable form of optics for bars such as those we've printed In recent tests. The larger the area of the opening, the greater the amount of the bar which is sensed. The narrower the effective aperture (whether or not a fens is used), the higher the density can be made.

NRZ, ANYONE?

I was very glad to see your article on bar coding, and I hope it will be a success. There are a couple of improvements I'd like to see, though.

Since you're printing the bar code, won't you please print the same data in human readable form, too? The Universal Product Code has the numbers printed. Punch cards have their problems, but at least with them you can tell exactly, character for character, what's going into the machine. With paper tape (or your bar code formats) you can puzzle it out, but only with a lot of work. Of course, with magnetic tape there's no hope. You're suggesting 50 bits per inch [not anymore] so you could print the corresponding hexadecimal characters immediately below the bars at 12.5 characters per inch. (I've found 12 to 21 characters per inch in BYTE articles.) Of course, if you're printing ASCII characters, the characters

themselves could be used instead. If a misprint keeps one frame of bars from being read, I'd sure rather key in 125 hexadecimal characters than 500 painfully deciphered bits.

Since bar codes can be the same as saturated magnetic tape codes, I'm surprised you didn't suggest the NRZ (Non Return to Zero) code. In it, the medium is divided into equal cells. A transition (from white to black or black to white) in the center of a cell represents a one, while no transition represents a zero. A transition also occurs at the end of every cell for timing. Although more difficult to read manually than your formats two or three, this code has even spacing and is more compact:

1 1

* JEO_

T.B TO ■

0

1 1

0

1

0 0 0 0

If we assume, in each of these formats, that the short spaces and bars are half the width of the long spaces and bars, and that 50 bits per inch is a reasonable density for format 2, we can calculate the corresponding densities for the other formats:

Density Format (bits per inch)

1 75-150, average 100

2 50

3 50-75, average 60 NRZ 75

[We have to figure out how to do it first. . . but maybe ... 7

I think the NRZ code with hexadecimal or ASCII characters would be a good compromise.

To encourage use of your bar code standard, BYTE could offer to convert data from tape to bar code for anybody at a standard price. That way other magazines, particularly those on small budgets like club newsletters, could use it. If it were only a few dollars a page, bar coding would be cheaper than cassettes (though slower to read) even for a "production run" of half a dozen!

Finally, a hard copy printer or even a typewriter can print a low density bar code: 010001101 can be scanned right

82

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Using software (although this may be premature), NRZ may very we/i be much more complicated to decode. But it may be worth trying. Since the format of the light and dark we print has no bearing on the hardware, provided we use bars with physical minimum size parameters set by an aperture standard, it only requires a night or weekend's worth of software and some experiments with PC layout tape, white paper, a darkroom and a camera to try out a different format at the bit level. In actual program object or source code, we plan to print an exact hexadecimal map of each bar code frame, thus allowing both hand and machine readable data entry.

SPACES CARRY NO INFORMATION?

Harold Mauch sends us this commentary, which we print with a few words at the end:

I would like to take exception to the choice of proposed format for the "Machine Readable Printed Software" described on pages 12-17, BYTE magazine for December 1976. Of the three formats described, the selected format (format 3, page 14, figure 1) has the least going for it.

• It is lower density than format 1 since the spaces carry no useful information.

• Contrary to the assertions of the author, the spaces provide only a marginal reference for discriminating wide from narrow bars.

• The hardware and/or software needed to implement format 3 is more complicated than that required to read either format 1 or 2.

Examination of the test strings on page 17 indicate the typesetting, lithographic and printing process is far from "perfect" in maintaining bar to space ratios. To compensate for this imperfection, author Keith Regli added a "bias computation and adjustment" to the space count, thus complicating the software.

Such ad hoc measures could be eliminated with format I. The printing process maintains excellent bar to bar and space to space ratios, but poor bar to space ratios. The lithographer may have over or under exposed the plate or the printing press may be running too much or too little ink. A more satisfactory approach for discriminating between wide and narrow bars is to compute the average of known wide and narrow bars (add the counts and shift left once). This provides a discrimination threshold with which other bars in the local area may be compared. The same procedure would

apply to wide and narrow spaces. Even with the addition of reference bars and spaces, the average data density of format 1 is 33% greater than format 3 and 60% greater than format 2.

While on the subject of reference bars, format 3 needs them also. If the data is a string of zeros, I claim that the printing variations evident in the test strings on page 17 will eventually confuse the decoding algorithm. This can be resolved by adding a reference or parity bar, preferably to each 8 bit byte. This required addition thus gives format 1 a 50% density advantage over format 3,

I presently use and prefer a signal conditioner circuit nearly identical to that described in author Merkowitz's article (page 81, figure 3). The super differentiator circuit of figure 4 is better for low density waveforms since the photo sensor output is nearly a square wave. However, when bar and space width is decreased to the dimension of the photo sensor's effective aperture (0.005-0.010 inch in my equipment), the photo sensor output looks more like a sine wave which does not differentiate into the narrow pulses required by the threshold comparator of figure 4.

One final note: My experience is that timing bits alluded to in figure 2, page 16, are required, not for timing, but to permit the signal conditioner detectors to stabilize. Referring to figure 3, page 81: When the photo sensor is resting on the white page before a line of code is scanned, the peak detectors will decay to the "white" level. This creates a severe white bias until the "black" peak detector stabilizes. The result is that the measured duration of the first few bars and spaces of a line will be grossly distorted and not suitable for data.

Harold A Mauch

Director of Engineering

PerCom Data Co

4021 Windsor

Garland TX 75042

The point about format 7 versus format 3 needs some comment. First, the format 3 spaces do carry useful information - they give the timing values needed to discriminate bit widths. The bias calculation is required also in format I, which will suffer from the same problems in the switching of the levels. (This problem is caused by the tendency of the system to take different amounts of time to change state from black to white than vice versa.) By using explicit black marks for each bit, at feast we are guaranteeing that each bit has the same biases (one rising edge to black, one failing edge to white). We don't care about bar to space ratios other than the fact that they are locally constant within a space of several bits retained in the running average of the input algorithm.

The startup bias also depends upon your detector design, and later conversations with several engineers suggests that the circuits of Fred Merkowitz's articles are overly complex for this application. . . CHB

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Have you written Software for your

Altair Computer?

The Altair 8800 computer-was the first micro produced for the general public and remains number one in sales, with more than 8,000 mainframes in the field. The wide acceptance of the Altair computer and its rapid adaptation to many diversified applications has truly turned the dream of the affordable computer into a reality.

Yet the machine itself, remarkable as it.is, represents only the beginning. The right Software, tailored to meet a user's specific requirements, is a vital part of any computer system. MITS wants to insure that Altair users everywhere have the best applications software available today and in the future. For this reason, a new MITS subsidiary, the ALTAIR SOFTWARE DISTRIBUTION COMPANY, has been formed. Its purpose: to acquire the highest quality software possible and distribute it nationally through Altair Computer Centers.

That's where you come in. The ASDC will pay substantial royalties to the originators of all software accepted into the ASDC library. If you have written business, industrial or commercial use software for the Altair 8800, ASDC wants to hear from you. It is the aim of the ASDC to stimulate and reward creativity in producing useful software that makes those dreams of "computers for everyone" come true. The ASDC will select only software that measures up to its high standards for system design, coding and documentation. The software will then be further documented and distrib

uted through ^^k ^^ Altair Computer Centers around ^^^^^j^^^^k the country.

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BITS™ Presents:

TV Typewriter Cookbook by Don

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Digital Logic Circuits by Sol Libes. An

invaluable tutorial background volume on digital logic, arithmetic, 10 concepts and interfacing to analog devices; written by one of the founders of the Amateur Computer Group of NJ. This book acquaints the reader with much of the terminology and background concepts of digital hardware. $5.98.

-Modern Operational Circuit Design by

^Active Filter Cookbook by Don Lan

caster. The chief chef of electronics Cookbooks concocts another gourmet appetizer. Run to this book when you need to find a starting point for the design of a filter for use in an electronic application. $14.95.

-Altair Design developed by Ensor

John L Smith. An absolutely essential introduction to the use and application of operational amplifier systems. The book contains both theoretical background information and practical circuit suggestions which can be used to advantage by the experimenter. $16.95 (hardbound).

— Electronic Projects for Musicians by

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Holiday.

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Altair Design 3 developed by Ensor Holiday..

Keep the loved ones busy while you use your system . .. give them any one or all of these computer generated Altair Design books to start them (or yourself) on endless hours of creative coloring. No other coloring books are quite like these unique books. $2.50 each.

Artist and Computer edited by Ruth Leavit. A visual treat, as you encounter reproductions of numerous works by computer oriented artists and read about these works in their own words. $4.95.

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Pie&se not«: Although our ads will change month to month, with few exceptions all previous books adver•.ised Are ay*u!able through BITS, A

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.Practical Solid-State Circuit Design by

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-Boolean Algebra by 6rice Ward. A

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— What to Do After You Hit Return of

PCC's First Book of Computer Games. This is PCC's first book of computer games, a compendium which includes descriptions of numerous games, and listings of 37 selected BASIC games. $8, new second edition.

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Digital Computer Fundamentals by Jefferson C Boyce. The way to a world of learning is through books. A great place to start, and to return from time to time, is the classical textbook. This new book from Prentice Hall is intended as just that. Topics covered include digital computer operation, basic computer circuits and concepts, Boolean algebra, implementing computer operations in hardware, communicating with the computer and related issues of coding schemes, detailed discussions of the control section, memory functions, arithmetic and logic functions, input and output functions of a classical computer, a chapter on computer programming and a final summary chapter on the details of a typical minicomputer design interpreted in the light of the more theoretical general concepts in the book. This book is excellent background information for the literate and well read hacker. Order yours today. $15.95 hardbound.

Adam Osborne's books An Introduction to Microcomputers, Volumes 1 and 2, are a

concise compendium of the technical details of microprocessors at the component (engineering) level. These are the source books for the system designer who plans to employ the microprocessor, or the advanced homebrewer who wants a dash of customization not found in commercial products.

Volume 1 is subtitled "Basic Concepts." This is the book which presents a framework of ideas concerning the design and use of small computers implemented with LSI. Topics include definitions of the microcomputer, fundamental concepts of logic and numbering characteristics of instruction sets, etc. $7.50.

__ Volume 2 is a much thicker (895

How

Buy and Use Minicomputers and Microcomputers

by William Barden. People have often asked us where to turn to get an introductory book about computers for personal use. One excellent place to start is How to Buy and Use Minicomputers and Microcomputers, William Barden Jr's instant summary of the small computer revolution, published by Howard Sams in mid1976. This is one of the first books of the "general introduction to computers" genre to be published with an emphasis towards the small computer and personal computing as it is being practiced these days, the book, written for the novice as well as the expert, surveys the technical details of the field in nine chapters and 10 appendices. This book is light (but essential) reading for the experienced computer person, and worthy of serious, concentrated perusal by the novice. $9.95.

page) detailed volume which complements the information in the first volume. This is the volume which fills in many of the details left out of the conceptual treatment in Volume 1. Here you'll find 19 detailed chapters on the engineering and logical specifications of products made by 16 different manufacturers, including in many cases reprints from the manufacturers' documentation as well as new materials provided by the author. Published in 1976, it even includes such processors as the MicroNOVA by Data General and the Texas Instruments TMS-9900 as well as the older 8 and 16 bit machines. Organization is by design type, and where parts of several manufacturers were intended for a given processor design such as the 8080, these are grouped into a single chapter. $12.50

COMPUTER

POWER

AND HUMAN REASON

»«;

. Computer Power And Human

Reason by Joseph Weizenbaum. This book is one which should be purchased or read for several reasons. If you're presently a programmer by trade or skill, you'll see a philosophy of computer use and abuse propounded. It's genuinely interesting, and definitely provocative if you reference the storm of letters, counter letters and counter counter letters which this book produced in the Association for Computing Machinery's SIGART newsletters during 1976. If you're a novice to the field, the tutorial and explanatory chapters of this book, which are aimed at the layman, will serve as an excellent background source which is also eminently readable, This includes an excellent and low level explanation of what an algorithm is, and how computers go about executing effective algorithms. $5.95 softbound.

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87

COUNTER

COMPARATOR

MICROPROCESSOR INPUT PORT

COMPARATOR

COMPARATOR

Figure I: Block diagram of an analog to digital converter. This diagram shows the functions of the various components of the converter. There are two inputs to the tristate register, one from the comparator and the other from the channel decoder. The input marked A is the output state control and the Input Enable Control line. The input marked B is the register input strobe line.

POTENTIALLY 16

CHANNELS TO SELECT

CHANNEL DECODER

I MICROPROCESSOR OUTPUT 3 | PORT

An Inexpensive Joystick Interface

Thomas R Buschbach In the quest to develop the ultimate in

12310 Purcell Rd video games, the need arose to interface

Manassas VA 22110 analog controls to a microprocessor. A com

mon control used in most video games is the joystick. It allows you to control two axes with one device. A joystick usually has potentiometers mounted on two adjacent sides as shown in photo 1. The potentiometers vary their resistance from 0 ohms to

Listing I: This 8080 op code will read the digital value for the desired analog to digital channel. The digital value is left in the accumulator. AH numbers in this listing and listing 2 are in octal.

address

octal code

op

operand

commentary

000

076 XXX

MVI

A,XXX

A:= number of desired channel;

003

323 AAA

OUT

AAA

output channel to unit AAA

005

333 BBB

IN

BBB

read digital value of channel from BBB

007

365

PUSH

PSW

save digital value;

010

227

SUB

A

clear accumulator and flags;

011

323 AAA

OUT

AAA

clear output port to 0;

013

361

POP

PSW

restore saved value;

their maximum value as the control stick is moved. The change in resistance is proportional to the displacement along the axis parallel to the surface the potentiometer is mounted on. All that remains is to convert these resistance values into digital values which the microprocessor can manipulate. To develop a full range of two and four player games, I decided four joysticks would be required. To interface four joysticks to the microprocessor would require eight channels of analog to digital conversion. Since the commercial analog to digital converters cost approximately $50, buying eight of them was prohibitively expensive. Even buying only one and multiplexing its inputs and outputs seemed to be more expensive than necessary.

Being a typical software fanatic, I had no desire to build my own analog to digital (AD) converter, However, after examining all the alternatives, I decided to build Roger Frank's circuit (BYTE, May 1976, page 70),

88

Photo 1: This is a typical joystick showing the poten tiometers that are mounted on each side of the device and wired in parai/ei.

which utilizes a digital to analog converter (DAC) and a software algorithm to do the analog to digital conversion. After ordering the required components I decided that using a software algorithm to do the conversion for eight channels of analog to digital conversion would not leave the processor time to process the game's algorithm. At this point I decided to implement the software conversion algorithm in hardware.

In developing the circuit I had four design goals in mind:

Interface at least four joysticks, eight channels analog to digital.

Use no more than one input and one output port.

Use no processor cycles for the conversion process.

Sample each analog signal at least 1000 times per second.

A block diagram of the circuit is shown in figure 1. The detailed functions of the digital to analog converter and the comparators are explained in Roger Frank's article mentioned earlier. If you are considering constructing this circuit, I would recommend reading that article.

The circuit is controlled by a counter which continually counts down from octal 377 to 0, driving the inputs of a digital to analog converter. The output of the converter is compared to the analog input signal from the joystick. As long as the converter output voltage is higher than the

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Figure 2: This is the schematic diagram for interfacing one joystick to a microprocessor. The portion within the dotted iines of the diagram should be repeated for each individual joystick in a system. All resistances are measured in ohms and are 14 W.

CO

o

voltage from the joystick, the output of the comparator is 0. When the counter has counted down to a value which causes the converter to output a voltage equal to, or slightly below, the voltage from the joystick, the comparator output goes high. This edge triggers the corresponding tristate register to load the current value of the counters. This occurs asynchronously for each channel.

To access the digital value for the desired channel, you output a number from 1 to 8, corresponding to the desired channel, on an output port. Leaving this value latched in the output port, the digital value may be read from the desired input port. Clearing the output port to 0 completes the operation. This operation is shown in listing 1.

Figure 2 is the schematic to interface one joystick to the microprocessor. The circuit may easily be expanded to handle four joysticks. The 74123, IC1, is used as a multivibrator to generate a pulse waveform. With the resistance and capacitance values shown it will have a frequency of approximately 0.3 MHz. This pulse train drives the count down input of the 74193 counters IC2 and IC3 which form an eight bit binary counter which continually counts from octal 377 (or hexadecimal FF) to 0. The outputs of counters IC2 and IC3 are tied to each tristate register pair (IC5 and IC6, and IC7 and IC8) and to the digital to analog converter, IC4. This latter circuit produces a negative ramp continually going from +5 V to 0 V in 256 steps. The output of IC4 is converted from a current to a voltage signal by IC9. One quarter of IC10 is used to compare the output of IC9 to the voltage from the joystick. The output of each quarter of IC10 is tied to a single tristate register pair. This output remains a logical 0 as long as the voltage from IC9 is greater than the voltage from the joystick. When the voltages are equal the output of the corresponding quarter of IC10 shifts to a 1. This edge triggers the corresponding pair of registers to latch the value of the counters at

Table I: Power connection table for the circuit of figure 2

Number

Type

+5 V GND -12 V +12 V

IC1

74123

16

8

IC2

74193

16

8

IC3

74193

16

8

IC4

MC1408L-8

13

2

IC5

74173

16

8

IC6

74173

16

8

1C7

74173

16

8

IC8

74173

16

8

IC9

LM301

IC10

LM339

12

IC11

7442

16

8

IC12

7404

14

7

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Photo 2: Underside of finished assembly showing wire wrap board and two joysticks.

Photo 3: This is the top view of the finished unit showing the two control sticks; the connectors are for input port, output port and power. An identical box with two more joysticks will plug into the side of this box for games requiring four joysticks.

Listing 2: This subroutine will read the digital value from a requested analog to digital conversion channel, set minimum and maximum values, apply a scaling factor, add or subtract an offset value, and then return the resulting value in the accumulator to the calling program. The program can be located at any high order address, symbolized by <x> in the listing.

octal

address

octal code

label

op

operands

commentary

000

176

MOV

A,M

A:= channel number;

001

323

002

OUT

2

output channel number;

003

333

002

IN

2

input digital value;

005

043

INX

H

HL: = HL+1;

006

107

MOV

B,A

B:—digital value;

007

227

SUB

A

I

010

323

002

OUT

2

clear output port;

012

176

MOV

A,M

A:=minimum value;

013 014

270 332

020 <X>

CMP JC

B JP1

(

if B>A then go to JP1 [not lower limit]

017

107

MOV

B,A

else B:=A [set lower limit] ;

020

043

JP1

INX

H

HL: = HL+1;

021

176

MOV

A,M

A:=maximum value;

022 023

270 322

027 <X>

CMP JNC

B JP2

I

if B<A then go to JP2 [not upper limit]

026

107

MOV

B,A

else B:=A [set upper limit] ;

027

043

JP2

INX

H

HL: = HL+1;

030

227

SUB

A

clear accumulator and flags;

031

206

ADD

M

A:=A+scale factor;

032

372

054 <X>

JM

JP3

if scale factor negative then go to JP3;

035

312

070 <X>

JZ

JP4

if scale factor zero then go to JP4;

040

127

MOV

D,A

D:=A;

041

170

MOV

A,B

A: = B;

042

027

JP5

RAL

shift left;

043 044

067 077

STC

CMC

I

clear carry;

045

025

DCR

D

D: = D-1;

046

302

042 <X>

JNZ

JP5

if D^0 go to JP5;

051

303

067 <X>

JMP

JP6

go to JP6;

054

346

177

JP3

ANI

177

mask most significant bit;

056

127

MOV

D,A

D:=A;

057

170

MOV

A,B

A: = B;

060

037

JP7

RAR

shift right;

061 062

067 077

STC

CMC

i

clear carry;

063

025

DCR

D

D:=D-1;

064

302

060 <X>

JNZ

JP7

if D is greater than 0 go to JP7;

067

107

JP6

MOV

B,A

B:=A;

070

043

JP4

INX

H

HL: = HL+1;

071

227

SUB

A

clear accumulator and flags;

072

206

ADD

M

A:=offset value;

073

372

100 <X>

JM

JP8

if most significant bit =1 then go to JP8

076

200

ADD

B

A:=A+B;

077

311

RET

return;

100

346

177

JP8

ANI

177

mask most significant bit;

102

127

MOV

DfA

D:=A;

103

170

MOV

A,B

A: = B;

104

222

SUB

D

A:=A-D;

105

311

RET

return;

that instant. All tristate register outputs are normally in the high impedance state. To access a register you output the number of the desired channel on an output port. The 7442, IC11, decodes the four least significant bits of the output port to determine which register pair to enable the outputs on; at the same time disabling the inputs of the register pair so that the registers will not be updated while the microprocessor is accessing them. A 0 on the output port places all tristate register outputs in the high impedance state.

Construction Notes

Resistor R4 is used to set the maximum digital value possible. Set all data inputs to the digital to analog converter at +5 V, then set R4 to yield the desired digital value. This sets all analog to digital converter channels simultaneously. If it is required to adjust a single channel's maximum value then a resistor must be added in series with the joystick, such as R15. A value equal to the joystick's internal resistor would cut the full scale digital value in half. Note that the maximum value may also be limited by software as is done in listing 2, but this does not utilize the full displacement of the joystick, as using R15 would.

The +5 V at the joysticks must be regulated and free from noise. Any fluctuations in this voltage will cause fluctuations in the digital value. Depending on your power supply and wiring, it may be necessary to provide a zener diode for on board regulation of the +5 V supply. Also, be sure to use several bypass capacitors.

Software Control

The subroutine of listing 2 will read the digital value from the requested analog to digital conversion channel, set minimum and maximum values, apply a scaling factor, add

92

or subtract an offset value, and then return the resulting value in the accumulator to the calling program.

A control block must be set up for each analog to digital channel. The address of the control block must be loaded into the HL register pair prior to calling the subroutine. The control block of 5 bytes must be in the following format:

Starting address

+1 byte +2 bytes +3 bytes +4 bytes

Channel number

Minimum value Maximum value Scale factor Offset value

The first byte, channel number, selects the desired pair of tristate registers. It is the binary coded decimal number which when output to the analog to digital converter unit will cause IC11 to enable the desired register pair.

The second byte, minimum value, determines the absolute minimum number that is accepted from the converter. If the value from the converter is smaller than the minimum value it is set equal to the minimum value.

The third byte, maximum value, determines the absolute maximum number that is accepted from the converter. If the value from the converter is larger than the maximum value it is set equal to the maximum value.

The fourth byte, scale factor, determines by what power of two the raw digital data will be scaled. Scaling is accomplished by the new value set equal to the raw data times 2 raised to the power of the scale factor" where the scale factor is any value from —127 to +127. This yields the following possible factors (. . . 8, 4, 2, 1, .5, .25, .125, . . .). A one in the most significant bit signifies a negative scale factor.

The fifth byte, offset value, is added to the digital value after the scale factor is applied. It may be any number from —127 to +127. As a two's complement integer, a one in the most significant bit signifies a negative offset.

Conclusions

The final assembly of this circuit, shown in photos 2 and 3, was built into an aluminum housing on a wire wrap board. The circuit can be used to interface any analog voltage signal to a microprocessor. The circuit for interfacing two joysticks to the microprocessor was constructed for about $35, exclusive of the cost of the joysticks. For an additional $10 the circuit could be increased to handle four joysticks."

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93

Continued from page 16

Popular Electronics Cosmac ELF project, has a possibility of expansion without too much complexity. The processor was obviously designed with the notion that software is cheaper than hardware (sometimes) and the 1802 can be programmed to replace hardware in many ways.

One such way is using a programmable output line as a memory extension address bit. The processor has a Q line output which can be programmed in software to be either high or low. This could be used (properly buffered of course) as an address bit to select a page of memory. This would allow expansion of its address to 17 bits very simply and allow 128 K with very little hardware and also very little software.

I don't intend to be even in the 64 K range for quite some time but those who could use 128 K now can get it easily. Thanks also for the "Beer Budget Graphics" article in the November issue, page 26.

John Pawlicki

6065 Greenwycke Ln

Monroe Ml 48161

The same general technique is what is meant by adding bank selection logic to a machine. Several processors have similar opportunities for expansion, For example, the National Semiconductor PA CE 16 bit processor has 4 programmable flag outputs - treating those flags as address bits externally results in a total of 20 bits worth of memory address space, or a maximum of 1,048,5 76 words of memory.

ARE ANY READERS USERS OF SURPLUS DATAPOINT MACHINES?

I've been reading BYTE since the August 76 issue and have enjoyed it quite a lot. It is nice to know there are so many computer freaks out there. The reason I'm writing is that I used to work for Datapoint Corp as a technician. I had a Datapoint 2200 Version II to use for test purposes. It is an 8 bit TTL minicomputer and is fairly fast and powerful. It has a built-in 80 character by 12 line CRT display, a keyboard and a dual cassette deck. Although it has only 16 K of programmable memory, I found it more than adequate with the 2 cassettes with 110 K each, and disk operating software is available. There is a large amount of high level software (including timesharing) available including several excellent diagnostic programs (capable of identifying which memory chip is bad, for example).

They have made over 5,000 of these minis since 1973 and they are available in the used market. I have read of amateur use of the PDP-8, but there has been no mention of the Datapoint. Is there anyone else out there interested in this mini?

Bill Doyle

A COMMENT ON BUG OF THE MONTH #4

The solution to "Bug of the Month #4," in October 76 BYTE, page 41, overlooks an important point. I think it is logically correct after handling the N=2 case and moving statement K=1 to precede the last RETURN as suggested. However, the program (or any program) does not run in a clean environment. Any computer that a FORTRAN compiler or interpreter runs on has a limited integer range. If the value of N to be tested is prime and near the maximum integer that can be represented, the computation 1*1 will result in integer overflow. This is particularly a problem in FORTRAN as some versions do not give error indications on integer overflow.

As an example, I checked this problem using a version of WATFIV on an IBM 370. Integer overflows do not give an error. The maximum positive integer is 2,147,483,647 (2**31 -1). In the program the value of I is increased until 1*1 is greater than N, assuming N is prime. The largest value of I which will not overflow when squared is SQRT (2147483647) truncated or 46340. Any prime numbers larger than 46340**2 (2,147,395,600), but still within the integer range, will cause an integer overflow of I and improper termination. I consulted a prime number table and found they don't generally go up to 2 billion; however, there are probably plenty of prime numbers in this category.

Even in the case that an error message occurred on overflow, the routine is still not working correctly. While it would not result in potentially erroneous results, neither has an answer been returned to a perfectly reasonable request. For these large values of N, a possible solution is to simply check for the value of I exceeding 46340 following the I increment. If this occurs, N is then prime.

Unfortunately, this requires an extra operation in the loop and depends upon the computer's integer range. I have not been able to think of a better method.

Keep up the good work. "Bug of the Month" is usually interesting.

Richard Altmaier

POB 2061

Stanford CA 94305

CORRECTIONS FROM BOB MARSH

Three factual errors were included in recent issues of BYTE magazine regarding Processor Technology products:

1. Our Software No. 1 Resident Assembler, Editor Monitor package (referred to in the article as "SYS 8") was a joint development effort between Microtec and Processor Technology. Employees of PTC added many neat features to the original Microtec program in order to produce Software Package No. 1. It was first distributed

in July or August of 1975 in the form of well documented source listings. Paper tapes were distributed to many computer clubs free of charge. Other companies, including IMSAI and Tarbell, have since made use of Software No. 1 adding minor modifications to suit their IO device requirements. To my knowledge at least six other firms have reproduced Software No. 1 in one form or another, all of them giving PTC and Microtec credit for authorship. (All, that is, except one rather well known "surplus" dealer.) Please note that Microtec receives a small but well deserved royalty on each Software No. 1 we distribute. No other manufacturers are paying such royalties.

Software No. 1 is currently available from Processor Technology for $14.50 including both source listing and hexadecimal object paper tape or CUTS/BYTE standard cassette.

2. A recent review of our VDM-1 Video Display Module stated delivery as 60 days. In fact VDM-1 s have been available ''off-the-shelf" since October of 1976. There is no excuse for any of our 40 or so retail distributors to be out of stock for more than a few days. With good planning they should always have VDM-1 s, as well as our 2KRO, 3P+S, 4KRA and 8KRA modules, in stock.

3. In your review of the Sol computer system you added $97 for our CUTS audio cassette data interface. The Sol has its own CUTS type interface built in and does not require an additional module for this function. (The CUTS board is primarily used in Aitair and IMSAI mainframes.) So the system pricing in your example should be:

Sol-20 kit

$ 995

SOLOS module

100

TV/monitor

150

Cassette recorder

100

8KRA

295

Software

48

$1688

Bob Marsh Vice President

Processor Technology 6200 HollisSt

Emeryville CA 94608

COMMENTS ON HOME COMPUTERS: FIND A NEED AND FILL IT

Find a need and fill it! Henry Kaiser built quite a business organization using that phrase as one of his business precepts. And now the development of microcomputers and microprocessors has created a market for home use.

There are many functions in the home that can be carried out by microcomputers because of their unique properties that could not be effectively performed before. They include financial information, inventory of assets, inventory of food and supplies, energy control, recreational games and surveil

94

lance for theft and fire. You can probably think of more uses.

A whole new industry is being spawned and it does not detract from other industries because new needs are being created. It can create new job and career opportunities for persons familiar with computer usage.

What should be the marketing effort? Should it be structured like the auto industry with franchisee dealers and new models coming out every year or should it be structured like the radio and television industry with dealers carrying a multiplicity of models? Time will tell.

I would like to see demonstration models placed in places like Newport's Fashion Island or Glendale's Galleria or Los Angeles' Broadway Plaza.

W Donald Pollock 149 S Burlington Apt 2 Los Angeles CA 90057

WANTED: HIGH BANDWIDTH TV MODS

I see many articles and projects on converting televisions to video terminals for use on minis and micros. Unfortunately (for me), these are all set up to generate a 32 character line. I would like to build a terminal using a TV or video monitor that would have 80 or 72 characters per line. Isn't there a kit or some way of bypassing the front end of a TV that will let you get the bandwidth needed? And just how does one figure out the bandwidth that is needed? Does anyone out there have the schematics or logic diagrams for such an adventure? Any help is really welcome.

|oe Heck

12 Enfield St

Jamaica Plain MA 02130

Any authors out there engineering a commercial TV mod which fits this bill? Or is it even possible?

AUTHORS TAKE NOTE: 488 BUS INTERFACE WANTED

I have never written to a magazine, but as I have never enjoyed a publication as much as BYTE, I felt I just had to sit down and let you know how I feel.

I got into programming in a small way a few years ago, with the HP-65 and programming became a new love. I am the Electronics Section Supervisor of the Metrology Laboratory at Puget Sound Naval Shipyard. We have recently acquired an Altair 8800a with 20 K programmable memory, a TTY, 8 K and extended BASIC, and a 4P lO board with 4 ports. We are presently using the Altair for data processing and scientific calculations, but hope to use it in the future as an automatic instrumentation controller.

This brings up a point: I sure would like to see marketed or published a design for an interface from the Altair bus or standard 8 bit parallel ports to the IEEE 488-75 bus. The use of a micro

I

I

I

I

I

I

I

I

I

I I

What good is a Micro-Computer if you con't moke it work?

Startup time on micro-computers can be a real problem. We know that. That's why we've developed The Mini-Micro-Designer. The first complete package of hardware, software and educational materials. All with one purpose: to speed microprocessor system design.

How? By providing the only microprocessor test and development system with solderless breadboarding capabilities. At its heart: the 8080A processor chip, providing all signal functions. A

panel that monitors the address and data busses of the microprocessor and allows data I/O with or without an asynchronous terminal. And the Bugbook V, E&L's innovative approach to selfteaching micro-electronics.

So experiment. Design. Test. Because now there's a system that's caught up with imagination. The Mini-Micro-Designer from E&L Instruments. Available now at your local computer store. Suggested resale price $422.50 (U.S.A.)

t I I

E&L INSTRUMENTS, INC.

61 First Street, Derby, Conn. 06418 (203) 735-8774 Telex No. 96 3536

95

computer and a terminal with this interface would give the calibration instrumentation industry an inexpensive and versatile automatic test system.

Bruce O Ferland

PS: Am very excited about machine readable, printed software (bar codes). Hope to see some hardware marketed in the near future.

FREEDOM OF ENTRY

Wilber and Fylstra's sneers at computer professionals in the article "Homebrewery versus the Software Priesthood," October BYTE #14, page 90, are both unnecessary and unsupported. To believe that the industry, its managers, or its programmers encourages the present high cost of designing and maintaining software is stupid. Manufacturers normally lose money on systems software that they must develop to sell their machines and want lower costs and greater flexibility reliability (how much does a new release of an operating system cost?) more than anyone. The wide acceptance of such new techniques as top down structured programming, proofs of program correctness, chief programmer teams, and relational file organization indicates the interests of the profession in improving clarity, reliability and productivity.

The demand for computers and programs is very elastic (total spending for these things increases as prices drop). I and other programmers have more work than we need. We are happy to have people learn programming.

For those who did not see the article, Wilber and Fylstra accused the profession:

1. of deliberately surrounding computers with an aura of mystery;

2. of protecting their privileged posi

tions by keeping their knowledge to themselves;

3. of regarding their knowledge as sacred and beyond the nonspecialist;

4. of being high priests and acolytes of the holy alliance of logic.

AH of these charges are false.

In its growth and achievements, the computer industry has been the most dynamic enterprise in this country. We, the computer hobbyists, exist because of this success, not in spite of it. Both politically and psychologically, the computer industry is remarkably free of barriers to entry. I have no license or certificate. I have no college degree yet. I was able to get a position as a programmer analyst with no previous experience largely because of my experience in home computing.

Wilber and Fylstra are idiots. They get a minus infinity on BOMB from me.

The December 1976 BYTE was one of the best ever. Keep up the (usually) good work.

Martin Buchanan

2040 Lord Fairfax Rd

Vienna VA 22180

See Mike and Dave's comments in their fetter replying to H T Gordon's comments in December. They apply equaiiy here. Wouid anyone else care to comment?

IS THE SOFTWARE

PRIESTHOOD CONCEPT

CONSIDERED DANGEROUS?

In his letter concerning the evaluation of microprocessor instruction sets, December 1976 BYTE, page 50, HT Gordon misunderstood the main thrust of our article, "Homebrewery versus the Software Priesthood," October 1976 BYTE, page 90: Of course professional

software people will always be needed by business executives to help evaluate commercial products — that's not our point! We decry only those software people who, like some priests, seek to protect their knowledge of the programmer's art, as opposed to their product. We were concerned with the personal market, not the very different commercial market, and we fundamentally wish to encourage widespread software literacy and free exchange in this personal computing hobby.

Our recognition that there is room for journeyman programmers in the computer business should be clear from our discussion of their relation to the personal computing user. It is important, however, to carefully distinguish the two worlds. In the business world, the programmer's relationship to the client is typically that of an employee or a contractor. By contrast, the firm supplying software for personal use hopes to have a large number of individual customers. The salient distinction is of accountability: The parties to a software transaction are much more closely related in the first case than in the second. A commercial client can reasonably expect the software product to suit its intended application, but any individual user of commercially supplied "personal" software represents only a tiny portion of the supplier's intended market. Point one: Individuals wanting personal computers responsive to their own needs must be prepared to program the computer themselves.

On the other hand, if a lot of people know how to program their own computers, then somebody else stands to lose. That somebody else, though, hardly includes everyone paid to write computer programs. While people won't buy something they could easily do better themselves, they are generally happy to

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96

pay for quality merchandise. The essential factor here is the quality of the product. If individual users find it easy to produce fairly good programs, they'll only buy the really good stuff; the only losers will be the producers of mediocre goods. On the other hand, if ignorance is rampant, the less competent programmers can flourish in the personal market. Point two: Only the second rate practitioners stand to gain by a lack of wide scale diffusion of software skills.

Now, most hackers learned what they know for free, and they learned it through personal contact with other hackers. This has almost always happened where they were in close proximity. However, hobbyists, who currently represent almost the entire community of people making personal use of computers, are dispersed geographically. A good system of communication is necessary to bridge the distances. Telecommunications, with its very high transmission speed, can do wonders in helping people share consumerist views of the market as well as actual programs. The telephone brings personal telecommunication into a fantastically large proportion of people's homes, but it has the disadvantage of requiring both parties to a communication to be at home and disposed to communication at the same instant. That's why we proposed a network of "Community Information Exchanges" to serve as buffers to communication. Point three: A CIE net can be of immense utility in dispelling ignorance.

To close the circle, we had no intention to put anybody down; the ideas we're pushing are that a lot of people should learn to use computers well. That'll benefit all the good guys; and there's a plausible sounding mechanism by which we can pull it off. We disparage only those who, for whatever reasons, try to prevent it.

MikeWilber

920 Dennis Dr

Palo Alto CA 94303

David Fylstra

POB 10051

Stanford CA 94305

One point of information, which was not available to Mike or Dave, or Martin or H T Gordon at the time of writing of their respective letters: The results of a recent survey of a random sample of BYTE's 2100 readers out of our list show that they tend to be people with some experience in software with the following numbers:

51% indicated prior experience with any large computer system.

58% indicated prior experience with a minicomputer.

79% indicated that they intend to use (52%), or are using (27%), their personal computer system for software development.

The numbers for various specific professional and business applications goals

such as text editing, accounting, or simulation were typically 30% in the ''intend" category with '5 to 10% indicating the "actually using"category.

This tends to indicate a significant overlap between professional people and personal computing users so the issue may be a moot one.

WHAT'S AN APPLE?

I am thinking about purchasing an Apple II minicomputer, but before I purchase it 1 would like to get as much information as possible about it. I wondered if you have heard about this computer or if you had written a product description about it in a past issue. If you could send me any information on it, I would appreciate it very much.

Andrew McNelly

1176 Berkshire Dr

San Jose CA 95125

/ saw the prototype in operation on Saturday November 20 1976 in Palo Alto CA in my hotel room when Steve Jobs and Steve Wozniac, Apple's creators, demonstrated it. It wilt be an excellent product, completely preassembled, available at computer stores nationally as well as by mail order. A 6502, 6 K ROM BASIC, color graphics, completely

assembled case and keyboard, 4 K program memory, audio interface, monitor program, etc, ail for about $1300. Go to a Homebrew Computer Club meeting and ask people about it, . , CH

HIGH LEVEL DECODING PROBLEM?

Thank you!

As an owner of the SR-52 (and printer), I was delighted to see your articles in the December issue. Programmable calculators, such as the SR-52 and HP-95/97, represent very powerful tools when one must deal with number systems.

I've just about finished a mini Star Trek game. Each time you get a Klingon, the display flashes "BLOOIE" (310078, upside down).

I hope you continue to set aside a small portion of your magazine for these hand held computers.

Meanwhile, my Motorola 6800 evaluation board is waiting in the wings for an RS-232 peripheral.

Tom Handley

New Age Communications

Portland OR

FVS: You can reprint this letter if you can decode my terrible writing. (No software provided!) ■

If you want a microcomputer with all of these standard features • • •

• 8080 MPU (The one with growing software support)

• 1024 Byte ROM (With maximum capacity of 4K Bytes)

• 1024 Byte RAM (With maximum capacity of 2K Bytes)

• TTY Serial I/O

• EIA Serial I/O

• 3 parallel 1/O's •ASCII/Baudot terminal compatibility with TTY machines or video units

• Monitor having load, dump, display, insert and go functions

• Complete with card connectors • Comprehensive User's Manual, plus Intel 8080 User's Manual • Completely factory assembled and tested —not a kit

• Optional accessories: Keyboard/video display, audio cassette modem interface, power supply, ROM programmer and attractive cabinetry... plus more options to follow. The HAL MCEM-8080. $375

• • .then let us send you our card*

HAL Communications Corp. has been a leader in digital communications for over half a decade. The MCEM-8080 microcomputer shows just how far this leadership has taken us... and how far it can take you in your applications. That's why we'd like to send you our card—one PC board that we feel is the best-valued, most complete

ffl

microcomputer you can buy. For details on the MCEM-8080, write today. We'll also include comprehensive information on the HAL DS-3000 KSR microprocessorbased terminal, the terminal that gives you multi-code compatibility, flexibility for future changes, editing, and a convenient, large video display format.

HAL Communications Corp.

Box 365,807 E. Green Street, Urbana, Illinois 61801

Telephone (217) 367-7373

97

Uiil.i

Microprocessor

Quay 80MPS.

For serious

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Quay 8GMP5 is nor designed for fhe cosuoi hobbyist. Only if you're serious about your personal computing, should you rind out about Quay dOMPS's features, capabilities, and options. Only if you want to break free from hobby-ciass microprocessors and enter a great new world of sophisticated computing experiences, should you get into the Quay 60MPS.

Features

D Single PC board. 16 pin c11"

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3 Z-60CPU.156if

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points; trace and single-step debugging; handles serial I/O.

7 additional UVEPROM sockets,

4 6-bit parallel f/O ports. Vectored interrupt (2 Z-60 PIO's, expands to 4).

O 1 socket for 2-60 4 timer.

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Dealer inquiries invited.

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At Last! A Phi Deck Tape Mass Storage System for the Altair Bus

Recognizing the .need for low cost versatile mass storage for the Altair and compatible 8080 based microcomputers, Micro Designs is offering two new digital cassette mass storage systems with up to one megabyte capacity.

According to the manufacturer, an integral part of these ready to use systems is a complete system of file management software which allows the user to manipulate both symbolic and binary files with high level commands.

The Micro Designs Model 100 is a compact single cassette drive which stores up to one half megabyte of data. The random access format of the data on

the tape allows programmed access to any single 128 byte record. The data transfer rate is 1000 bytes per second, and the tape may be searched at a rate exceeding 120 inches per second. The dual transport Model 200 puts up to one megabyte of peripheral files on line.

Both units come fully assembled, and ready for immediate use. The interface board plugs into the main frame motherboard connector to attach the mass storage unit to the computer. To bring up the operating system, the user loads a cassette, and transfers control to the ROM on the interface board; all further tape operations are automatic. Status lights inform the user of relevant tape conditions, and hardware error detection is provided. These small table top units sell for $550 (Model 100) and $825 (Model 200). Delivery is quoted as 30 days after receipt of order. Contact Micro Designs Inc, 1175 Colusa Av Berkeley CA 94707."

At Issue, a Table

We received the following item concerning a new products item in the December 1976 BYTE.

I wish to take issue with the comparison chart given in the "State of the Art Disk Technology" on the SA-400 Minifloppy. Specifically, the specifications on the 3M Minicartridge. When used with the Qantex Model 200 MINIDRIVE™, the 3M Minicartridge has an unformatted capacity of 336 kilobytes. With the high density option, the Model 200 will provide 676 kilobytes on one 3M Minicartridge. These numbers are computed as follows:

Capacity per track (unformatted) = Length of tape (feet) * 1 2 inches per feet • Packing density (bpi) 8 bits per byte

8 = 168 K For two tracks

Capacity = 336 kilobytes Thus, your figure of 100 kilobytes is completely erroneous.

The Qantex Model 200 is offered with either a 1 or 2 track head.

Next, let's consider transfer rate, which is computed as follows:

Transfer rate = tape speed (inches/

seconds) * packing density

(bits/inch)

Transfer rate = 30 ips ■ 800 bpi

Transfer rate = 24 kilobits per

second

98

Thus, an order of magnitude error in your chart. The Qantex Model 200 with the high density option provides a transfer rate of 48 kilobits per second.

Average access time is usually computed as one half the time required to traverse the media. The Qantex Model 200 provides a high speed mode wherein tape is moved at 90 ips. Access time is computed as follows:

_Tape length (ft) • 12 in/ft

Access Time

2 * Tape speed (in/sec) 140-12

Access Time

2 • 90

Access Time = 9.34 sec.

The Qantex Model 200 MINIDRIVE™ with intimate electronics is significantly smaller than indicated, with a physical size of 4 by 4.1 25 by 3 inches with a companion PC card of 4.5 by 6.5 inches. When packaged in an optional sheet metai enclosure, the complete drive including all PC cards is 4.75 by 4.75 by 7.5 inches.

Incidentally, the Qantex Model 200 configuration, which is equivalent to the type supplied by the SA-400, also costs $390, quantity one.

All things considered, I believe the decision to use a cartridge or disk must be founded upon careful analysis of system requirements. If access time is of key importance, the disk is the obvious choice, if capacity is of key importance, then the cartridge is the obvious choice. Other considerations might be the length of time it takes to validate a data block

just recorded. The rotational latency for the disk is 200 ms. Thus, the system has to wait 200 ms to validate a block just recorded. The Qantex Model 200 with a dual gap head will provide verification 5 ms after the last bit has been recorded. For many applications, this is a critical parameter.

Also to be considered is the MTBF of the two devices. The Model 200 MINIDRIVE' has only one motor as opposed to two for the floppy. Aside from the one motor, there is virtually no other mechanism for the Minidrive. The floppy, on the other hand, has the indexing mechanics to impart linear motion to the head positioning mechanism. Shugart's method for indexing is very clever; however, it does not appear to be able to operate in an environment of moderate shock and vibration. Qantex experience in producing the "standard" 3M Cartridge peripheral (AN/USH-26(V) for the Naval Electronics Systems has resulted in a cartridge drive which can operate in severe environments.

Joel A Kramer

President

Qantex Division

North Atlantic Industries Inc

200 Terminal Dr

Plainview NY 11803

Moral of the Story:

When putting in a new product item, the information is supplied by the producer of the product. Now, here is an oblique way of providing a new product item on the Qantex Model 200 MINIDRIVE-in the way of an interesting letter of protest over a tabfe found in December BYTE. As noted in the Shugart feature in December, the information, in the table on page 87, was "supplied by Shugart." A note of qualification concerning the Philips cassette drive was placed in the text because of the aval/ability of the Phi-Deck and similar low cost drives.

Manufacturing and marketing a product, any product, whether it be a computer, or one's personal services, is a very personal and people oriented activity. Products don't spring forth by magic but represent the creativity of the people working on their design and marketing. This letter emphasizes that fact. . . CH ■

Where to Go to Get Whatever . . .

The following text is taken essentially verba tin from a well written press release . . .

A new directory has just been published that helps radio amateurs, CBers, experimenters and computer hobbyists locate equipment, parts, supplies and services. Over 600 sources of standard and hard to find gear are listed in the handy guide. Many of the 600 sources are mail order firms and many are discounters, too. All are firms that do business with electronics hobbyists.

The first section of the book lists the

firms alphabetically, their complete mailing addresses and phone numbers. Then, a list of the products or services they offer are provided along with key product information, minimum order amounts, shipping charges, etc. You'll find everything from the million dollar mail order firm that handles hundreds of product lines to the weekend garage operation offering a low cost accessory for a microprocessor or Citizen's Band transceiver.

The second section of the book is a breakdown of products and sources in over 200 categories. Under each category is a listing of all firms that sell or manufacture the items cross referenced to the first section. For instance, there are over 25 sources of low voltage (1 2.6 VDC to 1 3.8 VDC) power supplies and over 50 sources of digital ICs.

The buying guide contains many prices and sufficient detail that you can make your purchases directly from the book or obtain additional information to make your choice. Catalog prices, if any, are listed.

The last section of the book includes all sources by state so you can buy from the firm nearest you when there are several choices. You'll probably find some local firms that you didn't know existed.

The Underground Buying Guide is available only by direct mail from Peninsula Marketing Services, 12625 Lido Way, Saratoga CA 95070. The price is $5.95 plus $.55 postage and handling. Californians add $.39 sales tax. Moneyback guarantee within 10 days if you are not completely satisfied."

Attention Commercial and Industrial Users of the 8080

muPro Inc, 424 Oakmead Pky, Sunnyvale CA 94086, has just announced what may be one of the best 8080 oriented assemblers to come to market. This is the BSAL-80 assembler, a "block structured assembly language" which comes with a relocating and linking loader. Finally, someone in the microprocessor world has gotten around

Microcomputer

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This dynamite new microcomputer system in a kit moves data like nothing else on the market. f\un it alone or plug it into an $100 bus AJtoir/IMSAI. For solo performance, all you need is *an unregulated power supply and on I/O device. Plugged in, Quay 8QAI is a CPU ROM, SIG, and RAM board—run any 5100 compatible device, BUT MORE THAN THAI Quay SOAI's Z-80 CPU opens challenging new areas of personal computing.

Features

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O Parallel keyboard Input. Accepts standard ASOi keyboard

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O 158 instructions. Ail 78 3080 instructions

D On board voltoge regulators.

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99

to implementing some of those nice things which systems programmers have grown accustomed to on the bigger minicomputer and large scale computers! This product, according to the press release, "allows the user to write programs in a high level language syntax while retaining the flexibility, program size and execution speed of assembly language. The ability to utilize any of the 8080 machine instructions and to control the use of the architectural features of the 8080 is maintained."

Since the output is truly relocatable and has linkage information, the programmer is able to develop truly modular programs. The company also has available a line number oriented editor program and a loader program to go with

the assembler. The product is definitely aimed at commercial users, since its price is well out of the range of the individual user on a tight budget: The BSAL-80 assembler with BSAL-80 relocating/ linking loader are available together for $975 in 8080 resident form: the BSAL-80 text editor is available for $350. The text editor, assembler and loader are available as a package for $1250 and a FORTRAN IV cross assembly version is available for $1250. The 8080 resident versions are provided free of charge with the purchase of the muPro-80, muPro-80E or muPro-80ED hardware and software development systems manufactured by the firm. Delivery of the software is quoted as immediate."

Cogitate then Emulate with This Bipolar Controller . . .

The new Signetics 8X300 bipolar microprocessor device is now available in a single board design evaluation kit intended to titillate the fancies of the hardware designer. . . but guaranteed to find its way into a few homebrew experimenters' hands as one of the cheapest, fastest and easiest routes to a high performance microprogrammable emulator for existing or experimental processor architectures. At $299 it's hard to argue with the features of this kit:

250 ns bipolar 8X300 processor. This processor handles 8 bits at a time with a read-modify-write cycle of 250 ns. (Yes, that's four instructions per microsecond!) 256 bytes of high speed working data storage. (In the use of this board as a microprogrammed emulator, this becomes the area used for the control data and general registers of the machine you emulate. If you're crazy enough to want to emulate a 360, for example, allocate 64 of these

bytes as the 16 general purpose registers and another 32 bytes for the four floating point registers and use the remainder for control registers and pointers within the emulator.)

• Four IO ports implemented to interface external devices. (You'd use these ports to drive the address and data buses of the emulated computer system.)

• System development software in PROM to aid you in utilizing the board.

• 1 3 bit address bus and 1 6 bit data bus for the microprogram memory used to drive the 8X300. (This should be more than enough control store to build the aforementioned 360 emulator. For a microprogramming project you'd want to add up to 8 K by 16 bits of dual port programmable memory to this bus.)

• Diagnostic and instructional controls which include a WAIT mode to allow single step operation, oneshot instruction jamming, ability to change or examine internal registers, etc.

Contents of the kit (hardware) include an 8X300 processor, eight 82S116 programmable memories for the data store, two 82S115 512x8 PROMs with the systems software for evaluation use, miscellaneous TTL parts, the printed

How to Use the 8X300 Controller as an Emulator

notes by Carl Helmers, Editor

CHOOSE MULTIPLES OF 8 BITS FOR ADDRESS AND DATA BUS TO MAIN MEMORY MODULES OF THE EMULATED MACHINE

This figure shows the conceptual design of an emulator system built around your present microprocessor and the 8X300KTI00SK kit of Signetics. The parallel IO ports of the general purpose microprocessor are used to address and load the programmable control store of the emulator (which you

8X300 IO PORTS USED AS BUS INTERFACES FOR THE EMULATED COMPUTER SYSTEM'S ARCHITECTURE

8X300KT100SK

EVALUATION

BOARD

13 LINES OF CONTROL STORE ADDRESS

16 LINES CONTROL PROGRAM DATA

CONTROL LINES TO 8X300

STATUS LINES FROM 8X300

PROGRAMMABLE CONTROL STORE (UP TO 8 K BY 16 BITS, HIGH SPEED MEMORY)

16 LINES DATA FROM CONTROL STORE

I CON

f STO

LINES \/_^/

ji 16 LINES DATA TO CONTROL STORE

CONTROL STORE ADDRESS SWITCH

CONTROL STORE ADDRESS SELECT

EMULATOR DEVELOPMENT PROCESSOR INTERFACE THROUGH PARALLEL PORTS

16 BITS ADDRESSING PLUS DATA 8 BITS AT A TIME

DMA (IF YOU'RE CLEVER) USES OLD PROCESSOR MAIN MEMORY AS SYSTEM MEMORY EMULATED MACHINE

YOUR OLD GENERAL PURPOSE PROCESSOR USED AS THE SYSTEM DEVELOPMENT PROCESSOR

A MASS STORE <

have to assemble yourself from high speed chips or run the 8X300 at less than its full rated speed). Assuming that you start with a complete computer system which includes assembler or high level language, you write the software of a microassembler in order to create the emulation programs conveniently prior to loading the control store. You use the IO ports of the evaluation card (plus additional ones if necessary) to define the address and data bus structure of the machine you're emulating, if you're clever, you make this output of the 8X300 treat your old microprocessor's memory as its own via the DMA trick, but for initial testing it is probably better to dedicate a small amount of memory (perhaps 4 K bytes) exclusively to the emulated machine to avoid blowups due to wild programming of undebugged machine instructions. Through the control and status interfaces you tack onto the evaluation board kit, you make the emulated machine treat the old machine and its peripherals as its main IO devices, so that programs working in the new architecture can at least talk to you. The result of all this cogitation and wiring will be a microprogrammable computer architecture experimental rig which will be the envy of many an industrial laboratory or university computer science department -yet still at a cost within the advanced experimenter's budget.*

100

circuit, complete manual and assembly instructions. Signetics is located at 811 East Arques Av, Sunnyvale CA 94086, and the 8X300KT100SK is available from Signetics distributors."

What Makes the Z-1 Tick?

Cromemco has forwarded this picture of Harry Garland's Z-80 processor card which is what makes their new Z-1 computer "tick." According to Cromemco, they have an arrangement with Zilog to obtain a selected version of the Z-80 processor which can operate with a 4 MHz clock. Yet the card remains compatible with the Altair bus which is available from numerous manufacturers.

This processor card design has a crystal controlled 4 MHz clock which can drive the processor at either 4 MHz or 2 MHz depending upon a switch selected option. The use of memory wait

states enables the board to operate with mixes of fast and slow memory in the event that an older system is being upgraded to the 4 MHz clock rate.

An interesting feature which will prove most useful to those people who purchase the Cromemco Bytesaver EROM card (or its equivalent) in order to build permanent systems software loads is the new Cromemco Z-80 processor card's power on restart option which allows selection of an automatic restart vector to any 4 K boundary in memory address space. Thus if you put your monitor in EROM up at hexadecimal address F000, this board lets you set up an automatic restart jump to your monitor whenever you turn on the power (or if you're a true hacker, when you simulate power on with your own restart button).

This processor is available either in kit or in assembled form at prices of $295 and $395 respectively. Delivery is quoted as 15 to 30 days ARO (after

receipt of order). Cromemco also provides a Z-80 monitor, with complete documentation including source code and paper tape object code. Also available according to the press release is a Z-80 assembler and BASIC interpreter. Cromemco is located at 2432 Charleston Rd, Mountain View CA 94043."

A Matter of Form

We recentty received a pad of coding forms for those who work in assembly or machine language, designed and sold by Walton Electronics. The forms are bound together in pads of 50 sheets and are formatted to accept code for the more popular microprocessors. Columns include: address, code, label, instruction and notes. Code can be written in either octal or hexadecimal with up to 3 bytes per line in regular assembler format. The lines are spaced to permit coding from a pica typewriter.

These forms make hand assembly easier and neater which helps eliminate errors. The pads sell for $1.95 each postpaid. Quantity discounts are available. Order from Walton Electronics, POB 503, Bethany OK 73008, or check your nearest computer store."

Explore the Universe of Color

Compucolor Corp, Norcross GA 30071, announced plans in December 1976 to begin marketing a new 8 color

personal computer, the Compucolor 8001, in early December. According to the press release, the Compucolor 8001 is a stand alone CRT and microcomputer with both computation and graphics capabilities.

It is programmed to handle simple or complex tasks, from color graphics and income tax records to checkbook balancing, education instruction, tutoring and a unique variety of computer games. The unit features BASIC language, a 19 inch display screen, keyboard and tape memory. Options are also available.

The Compucolor is being marketed through retail computer stores nationwide, and no price was quoted with the press release."

INTERNATIONAL DATA SYSTEMS, INC.

400 North Washington Street, Suite 200 Falls Church, Virginia 22046 USA Telephone (703) 536-7373

S100 Buss Cards (ALTAIR/IMSAl Compatible)

88-SPM Clock Module

88-UFC Frequency Counter Module

88-MODEM Originate/Answer MODEM

GENERAL PURPOSE PERIPHERALS

MCTK Morse Code Trainer/Keyer

TSM

USES

Your computer keeps time of day regardless of what program it is

executing. Applications include event logging, data entry, ham radio, etc

Measure frequencies up to 600 MHz. Computer can monitor multiple frequencies such as transmit and receive frequency.

Use your computer to call other computer systems such as large timesharing systems. Also allows other computer terminals to "dial-up" your computer.

Hardware/Software package which allows your computer to teach Morse Code, key your transmitter, and send prestored messages.

Use it to measure inside and/or outside temperature tor computerized climate control systems, etc.

Requires one eight bit output port. Use it to produce computer

music.

Temperature Sensing Module

DAC8 Eight Bit Digital to Analog Converter

Terms: Payment with order. Shipment prepaid. Delivery is stock to 30 days. Write or call for detailed product brochures.

KIT PRICE

$96.00

$149.00 $199.00

$29.00 $24.00

$19,00

101

Technical Fcpum

Comments on a Prototyping Bus

(See December 1976 BYTE, page 128.)

Webb Simmons

1559 AlcalaPI San Diego CA 92111

This concerns the proposal for a universal prototyping bus structure by David Washburn.

Mr Washburn raises some interesting points, none of which raise objections from me; however, when we dream let us dream boldly. It is not boldness to increase the address bus width from 16 bits to 18 bits. It is not boldness to replace the pseudostandard bus with an 88 connection bus.

A truly bold step for the address bus is to immediately go to 24 bits (3 bytes). The processor board can have two 8 bit registers, loaded by 10 instructions (but it does not matter how they get loaded), to supply the upper 8 bits of an address. The choice of which upper register to use would be based upon whether it is an instruction fetch. [Not necessarily possible to determine with any processor chip . . . CH/ In this way instruc

tions and data can be arbitrarily far apart. The actual loading of the upper address register should be deferred by one instruction time to allow for a jump into the newly selected memory block. Many variations on this theme are possible and none would be binding upon any user. Merely allow 24 bits and let each person do his/her own thing.

Similar reasoning suggests 24 bits for the data bus. [But why not go ail the way to 32 ? ? ? CH/ A person with true 16 bits of data may wish to use a Hamming code for error correction as well as (in lieu of) simple error detection. A 21 bit field is required to correct a one bit error in 16 bits (see the Data General description of their Eclipse computer). Once again a person may either use the extra bits or ignore them.

I rather like the thought of multiple inexpensive connectors, but why stop at two?

Some Comments on the Universal Bus Idea

M Faiman

Associate Professor of Computer Science

University of Illinois at Urbana-Champaign

UrbanalL 61801

David Washburn's comments in the December issue of BYTE on a universal bus structure are well taken. We ran into the problem he describes a couple of years ago when we started to experiment with microprocessors in our department. Every microprocessor, as your readers well know, has its own external signal configuration and protocol which all other devices— memory boards, 10 interfaces, etc, must match in order to form a working system. Changing processors, even if they cost a mere $25, necessitates a costly redesign of all the associated device interfaces. Since there are typically many of the latter for only one of the former, this is

obviously an expensive and, in most instances, impractical business.

Our solution, after studying the characteristics of the popularly available and projected microprocessors, was to design our own Modular Unified Microprocessor System - MUMS (1, 2, 3, 4). This system has undergone two design iterations since its inception, and its chief characteristics may be summarized as follows:

1. The hardware utilizes a fairly simple, uniform bus structure that is processor independent. There is one microprocessor per bus, and it and all other devices intercommunicate via a small set of generic signals (see item 5 below).

2. The bus signal protocol is chosen so that the most numerous modules in a system require only the simplest, ie: least expensive, interfaces.

102

Use three connectors or even four. When a user has no need for the extra connectors they can be omitted from the mother board. The standard board size might increase somewhat but the extra square inches will not be very expensive.

The 3 bit "speed code" set by each memory board seems to have no advantage over a one bit "data ready" signal from memory. Unless and until the data is truly ready the processor can do nothing sensible anyway. Many computers already allow for asynchronous memory with an indefinite wait for data ready, so this in not new.

Concerning standard peripheral device numbers, why not define them in the range from a low of zero to a high of 255? Then allow anyone to append one or two upper bytes to this low byte of standard assignments. The upper byte (or bytes) could be set with jumpers or dip switches. This will allow the spirit of standard device assignments and still let a user put them where he wishes.

For multiple processors (eg: 2) let us not overlook the possibility of Y shaped memory in which each processor gets its instructions from its own branch of the Y without conflicts with the other processor. For data the processors can share the common branch and most of the time both processors can run at near full speed."

3. To sidestep the spread in timing requirements of different processors the mode of communication on the bus is asynchronous. A particular advantage of this is that memory boards of differing access/cycle times can be used in the same system. (There is no need for the "speed code" number that Mr Washburn describes.)

4. Multiprocessing is accomplished with the aid of a TIE module and, optionally, a COM-UNIT. The former plugs into any MUMS bus and appears to the processor as a DMA device. From its other end a 4 wire line (10 MHz serial) can talk to a similar module on another bus for dual processor activity, or to the COM-UNIT — In process of design right now — which will handle communication between up to 16 processors.

5. The bus is physically implemented on a 72 pin connector (DEC compatible), as shown in the figure. Of these, the DATA, ADDRESS and POWER lines are self-explanatory. The others have mnemonic names, as follows:

r

16 K STATIC RAM

For ALTAIR / IMSAI / POLY 88

$459 kit

ASSEMBLED $529

• USES 4K STATIC RAMS-NO REFRESH

• VERY LOW POWER - LESS THAN 1 AMP

• Z80 FAST-200ns ACCESS TIME

• PROVISION FOR BATTERY BACKUP

• LOW PROFILE SOCKETS FOR ALL CHIPS

• EACH 4K ADDRESSABLE TO ANY 4K SLOT

• HARDWARE/SOFTWARE MEMORY PROTECT FOR EACH 4K

• SPECIAL PAGING OPTION ALLOWS UP TO 1 MEGABYTE ADDRESSABLE MEMORY

• LOW COST

CONSTRUCTION MANUAL $1.75

PAGING OPTION $9.00

QUANTITY DISCOUNT 5 BOARDS — 5%

10 OR MORE —10% DEALER INQUIRIES INVITED

OMNI SYSTEMS INC.

P.O. BOX 7536, UNIV. STATION PROVO, UTAH 84602

READER SERVICE NO. 198

I I

Featuring the

test equipment

and accessories

you've been

looking for in

money-saving,

easy-to-build

kit form.

And our new catalog also lists hi-fi, television, amateur radio products and much more ... nearly 400 quality electronic kits for your every interest. You'll find Heathkit building easy and enjoyable with our famous step-by-step assembly manuals. And we won't let you fail. Should you have the slightest problem, an experienced staff of technical advisors awaits your phone call. Send for your FREE catalog today. You'll see why quality* reliability and serviceability are familiar words to a Heathkit customer. Heath Company, Dept. 334-27, Benton Harbor, Michigan 49022

Heath Company, Dept. 334-27 Benton Harbor, Michigan 49022

Please send my FREE Heathkit catalog. I am not on your maiiing list.

Name

Address

nity

State

CL-627

— ___-<

I I

103

BD15

—

1A

2A

—

BD7 i

BD14

_

1B

2B

_

BD6

BD13

—

1C

2C

_

BD5 I

BD12

—

1D

2D

—

BD4 1

I DATA

BD11

_

1E

2E

_.

BD3 1

BD10

—

1F

2F

—

BD2 1

BD9

—

1H

2H

—

BD1

BD8

_

U

2J

—

BDO

Expansion

X X

1K

1L

2K 2L

X

X

BA15

—

1M

2M

—

BA7

BAH

—.

1N

2N

—

BA6

BA13

—

1P

2P

—

BA5

BA12

—

1R

2R

—

BA4 '

) Annoccc

BA11

—

IS

2S

—

BA3 i

f AUUntoo

BA10

—

1T

2T

—

BA2

BA9

—

1U

2U

—

BA1

BA8

—

1V

2V

—

BAO

Component

Side of Card

GND

—

3A

4A

—

GND )

k

GND

_

3B

4B

—

GND

+ 5

—

3C

4C

—

+ 5

> POWER

+12

—

3D

4D

—

+ 12

-12

—

3E

4E

—

-12 J

f

X

3F

4F

X

RST

—

3H

4H

—

A"C"R \ WAV

l

X

3J

4J

X

RAV

_

3K

4K

—

> MEMORY

X

3L

4L

X

I

WHD

—

3M

4M

—

WLD )

i

DGI

_

3N

4N

_

DGO

DMA

W

_

3P

4P

—

DMR

ISN

—

3R

4R

—

TW )

i

IGI

—

3S

4S

—

IGO I

i

I A3

—

3T

4T

—

JHI

INTERRU

IA2

—

3U

4U

—

TR5 i

IA1

—

3V

4V

—

rm- /

Foil Side of Card

CONTROL

MUMS Bus - Signal Layout

RST

— Power on reset

RAV

- Read Address Valid

(from processor DMA

device to memory or IO

device register)

WAV

- Write Address Valid

(similarly)

ACK

— Acknowledge (opposite

direction)

WLD

- Write Low Data byte

WHD

- Write High Data byte

DMR - DMA device Request

DGI/DGO - DMA Grant In/Out (daisy chained signal)

IO - Used in conjunction

with appropriate memory control signals to access an IO page.

ISN — Interrupt Sync (proc

essor generated)

IRi - Interrupt Request for

level i (i = 1,2,3)

lAi - Interrupt Acknowledge

for level i

IGI/IGO - Interrupt Grant In/Out (daisy chained signal)

IVV - Interrupt Vector Valid

(device to processor)

It is obviously beyond the scope of this letter to describe timing relationships in detail, but the interested reader may find particulars in references 2 and 4 below. ■

REFERENCES

1. Faiman, M: Modular, Unified Microprocessor System (MUMS), ACM Computer Science Conference Abstracts, page 19, February 1976.

2. Catlin, R W : MUMS: A Modular, Unified Microprocessor System, (50 pages, Technical Report UIUCDCS-R-76-809, University of Illinois, Urbana-Champaign), IEEE Computer Society Repository #R76-245.

3. Faiman, M, Catlin, R W and Weaver, A C: A Modular, Unified Microprocessor System (MUMS), Proceedings of the IEEE DISE Workshop on Microprocessors, pages 1-5, Colorado State University, August 1976.

4. Faiman, M, Weaver, A C and Catlin, R W: MUMS — A Reconfigurable Microprocessor Architecture, Computer, January 1977.

What's

Computer Power & Light

Gene Morrow, president of Computer Power & Light, a computer store located at 12321 Ventura Blvd, Studio City CA 91604, has sent along a brochure describing his firm's packaged 8080 processor system. The Computer Power & Light COMPAL-80 computer is a fully assembled system for homes and small

businesses, which includes the following main features:

• 8080A processor

• audio tape serial interface port

• Teletype or RS-232 serial port

• 12 K programmable memory

• 16 line by 64 character video display with full ASCII character set and graphics

• 9 inch high resolution monitor

• ASCII keyboard with capacitance switch mechanisms

• case and cabinetry with cooling phan, chassis connectors for interfaces, "turn key" configuration

• PROM monitor to eliminate the need of a costly front panel

• 10 K extended BASIC including formatted PRINT, double precision, all transcendental functions, etc.

The price on the above package of features is quite reasonable — for $1863

you get a completely assembled system which can be viewed and examined in Gene's store. Gene's press release claims that several systems already have been delivered including one which is in use at Mt St Mary's College in Los Angeles as part of a computer programming curriculum, another which is being used to keep track of inventory in a retail store in Santa Barbara, and another in an industrial laboratory. For more information, contact Gene at the store."

A New Version of SC/MP

National Semiconductor has now introduced a new version of the SC/MP processor (see Robert Baker's article in September 1976 BYTE, page 76). This newer version is implemented with a faster NMOS technology with the following essential points of improvement:

104

• Twice as fast in execution (3.58 or 4.0 MHz on chip crystal)

• One quarter of the power requirements (200 mW versus 800 mW)

• Compatibility with the previous product

• Single power supply

According to the press release, this new version is being sampled from the factory at $17.76 for single quantities and in 1 977 the production quantities of 1000 or more will sell "significantly below $10 each" when it becomes available in a plastic package. National Semiconductor also plans to have available a retrofit kit for present owners of SC/MP kits, which will allow conversion to the new processor. The price for this product is not yet announced.

This is the kind of processor which rapidly becomes a commodity part, and

can thus be buried into all manner of dedicated application products with appropriate read only memory software designs and special purpose peripheral hardware. For an example of such dedicated products, consider the dedicated electronic music synthesizer module: Hypothesizing a $2 to $5 price for a plastic package version of this computer, using perhaps 1 or 2 K of 2708 storage for control programs, and perhaps 1 K or so of programmable memory for parameters, it should be possible to engineer an inexpensive stand-alone music synthesizer module which will sit on a computer table and take orders through a high speed serial port and RS-232 level receivers.

National Semiconductor is located at 2900 Semiconductor Dr Santa Clara CA 95051. National Semiconductor parts and products are available through most nationwide electronic distributors."

Floppy Disk Controller

And a Hint about a Future Article

NEC Microcomputers Inc, Five Militia Dr, Lexington MA 02173, has a pair of the most advanced LSI devices available for peripheral control in microprocessor systems. This pair consists of the uPD372D floppy disk controller chip (now available at $54 in quantities of 1 to 24) and the uPD371D cassette controller chip (also available, in quantities of 1 to 24 quoted at $48). Both these items are available from a nationwide network of distributors, which in New England includes Harvey Electronics, Semiconductor Specialists and Sterling Electronics. Tim Schoechle, of the Technical Staff for Microprocessors of NEC, sent along the latest technical manual on

the floppy disk controller chip, for use as a reference in editing a forthcoming article by Ira Rampil which reviews both of these controllers.

When you buy one of these chips, you get a fixed purpose processor which is customized to the job at hand. As described in the 68 page uPD372D disk controller manual (dated December 3 1976, which we understand was written by Tim), the chip takes care of all the housekeeping and formatting requirements at the hardware level needed to create floppy disk records with IBM 3740 format, Shugart Minifloppy format, etc. It also generates and checks cyclic redundancy characters, can be synchronized with address marks or physical indices (so called "hard sec

tors"), and will handle up to four floppy disk drives through separate select lines. Furthermore, it has the capacity to overlap input and output control of two separate drives. Taking into account differences in hardware, the track to track stepping rate and stepping pulse width outputs are programmable, as is the sector size and data rate. A list of 13 drives with which the chip is compatible is given by manufacturer and model number. More detailed information will have to wait for Ira's article — but for the engineers or homebrewers who can't wait, the information is available from NEC or its representatives: Ask for the "uPD372D LSI Floppy Disk Controller Chip User's Manual.""

MVM 1024 Microprocessor Video

Module

* * *

*

$225

ASSEMBLE AND TEST

Sixteen 64-character lines, upper/lower case 128 character font.

Software-controllable reverse video characters.

Full read and write capability for both cursor position and character code.

Interfaces to any microprocessor: 8080, 6800, 6502, etc.

Scrolling, line/character insert/delete, etc. easily done with software.

THE SOPHISTICATED VIDEO MODULE FOR THE ADVANCED EXPERIMENTER

o Write or tall tor complete literature.

~Ar

Riverside

ELECTRON*; DESIGN WC.

1700 NIAGARA STREET * BUFFALO, N.Y. 14 207 716 875-7070

105

Flights of Fancy with the Enterprise

David Price 3901 Victoria Ln Midlothian VA 23113

Listing 1: The Star Trek program, expressed in BASIC. For notes on conversion to Aitair BASIC see the text. This version requires 9382 bytes of work space for the program text, 161 matrix elements, and 46 bytes of character string space. The approximate totai size requirement is thus 10 K bytes, plus the size of the BASIC interpreter itself. Using a 12 K extended BASIC interpreter, this program would thus require approximately 22 K of programmable memory in a typical microcomputer system. Hurrah for the 16 K chips!

10

m

30

40

SO

60

70

80

90

10 0

110

120

130

140

150

160

17 0

BO

SO

200

210

SO

230

240

250

260

270

30

90

300

310

320

330

340

350

350

370

310

390

430

410

420

430

440

450

450

470

410

4»0

500

510

520

530

540

550

SO

570

90

90

60 0

610

620

630

640

"65 0

660

67 0

STAR TREK

STTRi SPACE WAR SIMULATION

PROGRAM BY DAVID PRICE

REM *»*** REM **** REM **** REM «*** REM *•**

REM »••«**•««•***••••*••••«••*«*••••« *••«

DEF FNA<XXINT<X*RND< 1>+1>

DIM GC8*8J,ZSC 153, CSE63,X4C24]

TO=T»<FNA<20)+20)*100

E»3000

P-15

S-0

x$»

DEF FND<DXSQRC(Kn, lD-SU 2+ (KC I * 23 -S2) " 2)

Q1»Q2«S1 = S2 = FNA<8>

MAT C«CONC9,2J

CC2# 13-CC3* 13-CC4* n = Ct4#23*CC5*23«CC6j23— 1

CE W 13-CC 3*2>CC 5j IJ-CE7/2J-CC9, lJ-0

MAT D=Z£RC63

B9»K9»0

FOR I-I TO 8

FOR J-i TO 8

K3*B3«0

IF RND< IX.8 THEN 270

K3=FNA<3)

K9-K9+K3

IF RND< IX.96 THEN 300

B3»l

B9=B9+ 1

S3=FNA(5)

GCI,J]=K3* 10 0 + 63*10+S3

NEXT J

NEXT I

IF K9=0 OR B9»0 THEN 200

GOTO 357 0

IF Ql >* 1 THEN 38 0

Sl-Ql*)

IF 01 <- 8 THEN 400

Sl»Ql-s

IF Q2 >

S2-Q2«l

IF Q2 <»

S2«Q2»8

X-GCQUQ23/100

K3-INTCX)

B3-INTUX-K3)*10)

S3»GC CI, Q2J-< CB3* I0XCK3* 106) )

IF K3-0 THEN 52 0

PRINT "COMBAT AREA"* "CONDI TION RED"

IF SXK3MQG) THEN 520

PRINT " SHIELDS DANGEROUSLY LOW"

MAT K»ZERC3*3J

MAT Q»ZERC8,83

QCS1/S23-1

FOR |»l TO K3

GOSUB 3500

QCRl,R2]-2

KCI; 1 J = R1

KCI,2)*R2

KU*33»200

NEXT I

IF B3»0 THEN 650

GOSUB 350 0

QCR1,R23»4

FOR 1=1 TO S3

GOSUB 3500

QCRl,R23-3

THEN 42 0

THEN 440

The main objective of this version of the Star Trek game is to destroy all of the Klingon battle cruisers within 30 stardates. The Klingons and starbases are randomly positioned within a simulated galaxy. To help you better visualize this galaxy we use quadrant sector notation.

The galaxy is divided into a matrix of 8 by 8, or 64, quadrants. Each quadrant is further subdivided into an array of 8 by 8 sectors. The United Space Ship Enterprise, of which you are captain, has been assigned to seek out and destroy all of the Klingon invaders. You have at your disposal a bristling array of sophisticated weaponry including phasers, photon torpedoes, and an onboard computer, which are triggered by

Once upon a time there was Star Trek. During its brief but eventful fife as a television series it not only won acclaim from within the science fiction community, but was also hailed by the popular media as one of the first truly intelligent shows on television, it a d an entirely new type

of audience to science fiction including many from the computer crowd. By showing us glimpses of a distant future, it allowed us to take a more objective look at the present Star Trek now survives only in rerun form and in the games of computer people. Those computer people who happen to be Trekkies have adopted the Star Trek theme as their own. Everybody under the sun has been programming games based loosely on StarTrek. The- . < have evolved into some of the most complex computer games ever written. Yet, lurking beneath this complexity lies a startling amount of realism.

106

your direct orders. To utilize the facilities of the Enterprise you enter simple numerical commands. Figure 1 shows the flowchart for the initialization of the variables used in the program and the first quadrant set up. The flowchart also indicates on what lines of the program the various operations take place.

The Command Set

Figure 2 shows the flowchart for entering commands to the program. The commands are numbers which are tested by the program to determine what to do.

Command 0 places you in control of the warp engines which are used to propel the Enterprise from one location to another. You are first asked for the direction in which you wish to travel. The trajectory angles are arranged on a circular vector as shown in figure 3.

Listing 1, continued:

f START J

90

INITIALIZE VARIABLES

210

INITIALIZE

GALAXY

ARRAY

3570

3610

YES

440

OUTPUT INSTRUCTIONS

INITIALIZE QUADRANT

390

440

MOVE TO

LEGAL

QUADRANT

INITIALIZE QUADRANT ARRAY

2600

OUTPUT SHORT RANGE SCAN

(command J

Figure 7; Flowchart for the initialization of the Star Trek program. The numbers in the flowcharts of this article re fer to line numbers in the program found in listing L Once initialization is completed, execution flows to the command interpreter.

SO NEXT I

69 0 GOSUB 26 0 0

700 PRINT "COMMANDi";

710 INPUT A

T20 IF A<l OR A>5 OR A#INTCA) THEN 78 0

73 0 Rl-A+1

740 IF DCR13 >■ 0 THEN 78 0

75 0 GOSUB 342 0

760 PRINT ZS;- NOT OPERATIONAL

77 0 GOTO 700

T8 0 GOTO (A+l) OF 890* 1520* 1640* 1800*2200*3010*3550

WO PRINT

80 0 PRINT "Q-SET COURSE"; TABC 2 0) ; "4 3 2"

810 PRINT "1-LONG RANGE SCAN-; TABC 21) J "V * /"

820 PRINT -2»PHAS£R CTRL"; TABC 22) I -\V

830 PRINT "3-TQRPEDO CTRL"; TABC 18) J "5 - 1"

840 PRINT "4-SHI ELDS"; TABC 22>; V\"

850 PRINT "5-LIBRARY COMPUTER"; TABC 2 1); "/ ' \"

860 PRINT "6-RESIGNATION"; TABC 2 0); "6 7 8"

87 0 PRINT

66 0 GOTO 700

90 PRINT "COURSE C 1-9)1";

90 0 INPUT CI

910 IF CHI OR CI >- 9 THEN 700

920 PRINT "WARP FACTOR (0-g)iBi

93 0 INPUT VI

940 IF VI <- 0 OR Wl>8 THEN 700

950 IF DC 13 >- 0 OR VI <■ .5 THEN 98 0

96 0 PRINT "ENGINES ARE DAMAGED* MAXIMUM SPEED- WARP .5"

970 GOTO 920

930 IF E-CV1*8)»0 THEN 1030

99 0 IF S<1 THEN 247 0

1000 PRINT "YOU ONLY HAVE"; E; "UNI TS---SUGGEST YOU CROSS- OJRCUI T"

1010 PRINT -FROM SHIELDS* VHICH HAVE^/S; "UNITS"

102 0 GOTO 70 0

103 0 FOR I" I TO 6

1040 IF DC13 >- 0 THEN 1060

10 5 0 DC I 3-DC I 3+1

1060 NEXT I

1070 IF FNAC10)#5 OR Vl<2 THEN 1120

108 0 R1-FNAC6)

109 0 DC R13- DC R1 3 - FNAC 5)

110 0 GOSUB 342 0

1110 PRINT LINC 1)* "DAMAGE CTRL REPORTS *miZMm DAMAGED- '"*LIN< i)

1120 N-INTCV1*8)

1130 QCS1*S23»0

114 0 X-Sl

1150 Y-S2

116 0 C2»INTCC1)

117 0 X1-CCC2* 13+CCCC2+ 1* 13-GCC2* 13)*CC1-C2) 1180 X2»CCC2*23+CCCC2+ 1* 23-CCC2* 23 )* C C 1-C2) 119 0 FOR 1-1 TO N

£00 S1-S1 + X1

£10 S2-S2+X2

£20 IF SKI OR Sl>8 OR S2< 1 OR S2>8 THEN 1360

£30 IF OCINTCSI)*INTCS2)3=0 THEN 1270

£40 S1-S1-X1

£5 0 S2-S2-X2

£6 0 GOTO 128 0

£7 0 NEXT I

£80 S1-INTCS1)

£90 S2*INTCS2)

1300 QCS1*S23=1

1310 E»E-N

132 0 IF VKI THEN -69 0

1330 T=T+l

1340 IF T>T0+30 THEN 2500

135 0 GOTO 69 0

1360 X»Q1*8+X+X1*N

1378 Y»02*8+Y+X2*N

1380 Ql=INTCX/8)

1390 Q2-INTCY/8)

MOO Sl"INTCX-Ql*8+.5)

1410 S2»INTCY-Q2*8+.5)

1420 IF S1>0 THEN 1450

W3Q Ql-Ql-1

1440 Sl = 8

1450 IF S2>0 THEN 1480

146 0 02=Q2-1

W7 0 S2=*8

143 0 T-T+l

149 0 E-E-N+5

i500 IF T>TO+30 THEN 2500

£10 GOTO 360

1520 PRINT X$C 1* 173

1530 FOR 1*01-1 TO 81+ 1

1540 MAT N»ZERC33

155 0 FOR J-Q2-I TO Q2+ 1

1560 IF K! OH I>8 OR J< 1 OR J>8 THEN 1580

B78 NCJ-Q2+23-GCI*tJ3

158 0 NEXT J

1590 PRINT USING 163 0; NC 13 *NC 23*NC 33

1600 PRINT X$C 1* 173

1610 NEXT I

162 0 GOTO 700

1630 IMAGE -l "*3<3D*" I -)

1640 IF K3= 0 THEN 2350

165 0 PRINT "ENERGY AVAILABLE-"; E

1660 PRINT "NUMBER OF UNITS TO FIREi";

167 0 INPUT X

168 6 IF X< 1 THEN 700 1690 IF E-X<0 THEN 1660 17 0 0 E= E-X

17 10 FOR 1= 1 TO 3

1720 IFKCI*33-0 THEN 1780

1730 H=INT(X/K3/<FNDC 0)))

r?40 KCI*33»KCI* 33-H

1750 PRINT H;"UNIT HIT ON KLINGON"

1760 IF KCI*33>0 THEN 178 0

1770 GOSUB 2050

178 0 NEXT I

107

Listing J, continued:

1790 GOTO 2030

BOO IF P>0 THEN 16 3 0

BIO PRINT "ALL PHOTON TORPEDOES EXPENDED"

£20 GOTO 700

B30 PRINT "TORPEDO COURSE 0-9);";

B40 INPUT CI

B50 IF CHI OR CI >- 9 THEN 7 00

B60 C2»INT<Cl)

B70 XI-CCC2* U+CCCC2+ Ij IJ-CCC2* 13)*<C1-C2)

B6 0 X2-CEC2, 23+CCCC2+ U 21- CC C2, 2] ) *CC 1- C2>

B9 0 X«5 1

POO Y=S2

BIO P= P- 1

P2Q PRINT

S3 0 X=X+X1

19 4 0 Y=Y+X2

B50 IF X<1 OR X>8 OR Y< 1 OR Y>8 THEN 2 18 8

660 IF QCINT(X),INTCY)J»0 AND 61 INTCX+ - 5) * INTC Y+ - 5) I* 0 THEN 1930

B7Q FOR 1=1 TO 3

£30 IF INTCX)-KCI*13 AND INTCY)»KCI * 21 THEN 2020

B-90 IF INT<X+.5)=KCI, 13 AND INTCY+ . 5) -KC I , 23 THEN 2020

2000 NEXT I

2010 GOTO 2 12 0

2020 GOSUB 2050

2030 GOSUB 2370

204 0 GOTO 70 0

2050 KCXj3)-QCKC1, 13,KO,233=0

2060 PRINT "***KLINGON DESTROYED***"

2070 K3*K3-1

208 0 K9=K9-1

209 0 IF K9=0 THEN 2550 2100 GCQ1>Q23 = GCQ1,G23- 100

21 1 0 RETURN

2120 IF QONTCX),INT(Y)3#3 THEN 2150

2130 PRINT "YOU CAN'T DESTROY STARS* SILLY I •

2140 GOTO 2180

2150 PRINT "***STARBASE DESTROYED***"

2160 PRINT "YOU ARE HEREBY RELIEVED OF DUTY ! I CONGRATULATIONS I"

217 0 GOTO 2 53 0

218 0 PRINT "TORPEDO MISSED"

219 0 GOTO 203 0

22 0 0 PRINT "ENERGY AVAILABLE= mi E+5

2210 PRINT "NUMBER OF UNITS TO SHIELDSt";

2220 INPUT X

2230 IF X<0 THEN 700

2240 IF E+S-X<0 THEN 22 10

225 0 E-E+S-X

2260 S=X

2270 GOTO 700

2280 PRINT LIN< 1) ; "DEVICE"* "STATE OF REPAIR"

229 0 FOR Rl-I TO 6

2300 GOSUB 3420

2310 PRINT ZS/DCRU

2320 NEXT Rl

2330 PRINT

234 0 GOTO 700

2350 PRINT "SHORT RANGE SENSORS REPORT NO KLINGQNS IN THIS QUADRANT"

236 0 SOTO 7 00

2370 IF CS--DOCKED- THEN 2460

2380 IF K3=0 THEN 2460

239 0 FOR 1= 1 TO 3

atlOQ IF KII,33=Q THEN 2450

24 10 H=INT(KCI,33/FNDC 0)+ 1>

2420 S=S-H

2430 PRINT H;-UNIT HIT ON ENTERPRI SE"

2(140 IF S<0 THEN 2520

2450 NEXT I

246 0 RETURN

247 0 PRINT -** FATAL ERROR** "

248 0 PRINT -THE ENTERPRISE IS DEAD IN SPACE* AND MUST BE EVACUATED H"

249 0 GOTO 253 0

2500 PRINT LINO), "IT IS STARDATE"; T

2510 GOTO 2 53 0

2520 PRINT LINO);- ***THE ENTERPRISE HAS BEEN DESTROYED***"

2530 PRINT LINO), "THE FEDERATION WILL BE CONQUERED 1 I I"

2540 GOTO 3560

2550 PRINT

2560 PRINT "THE LAST KLINGON BATTLE CRUISER HAS BEEN DESTROYED! !"

257 0 PRINT "THE FEDERATION HAS BEEN SAVED If"

258 0 PRINT

259 0 GOTO 3 56 0

26 0 0 FOR I-SI- 1 TO $1*1 2i 10 FOR J=S2-1 TO S2+ 1

2620 IF Kl OR I >8 OR J< 1 OR J>8 THEN 2640

2630 IF QCI,J3=4 THEN 2670

2640 NEXT J

2650 NEXT I

266 0 GOTO 27 3 0

267 0 C*** DOCK ED"

268 0 E=300 0

269 0 P- 15

27 0 0 MAT D=ZER 27 10 S«0

2720 GOTO 28 10

2730 PRINT

2740 IF K3>0 THEN 278 0

2750 IF E<300 THEN 28 0 0

2760 CS="GREEN

277 0 GOTO 28 10

2780 CS*-*RED*"

279 0 GOTO 23 10

23 00 CS--YELLOW" 35 JO PRINT xs S20 Z=0

330 GOSUB 3330

940 PRINT

350 GOSUB 333 0

260 PRINT - STARDATE"; SPA< 5)i T 370 GOSUB 3330

380 PRINT -CONDITION-JSPA(5);Ci

39 0 GOSUB 3330

23 0 0 PRINT "ENERGY*"; SPAC 7); E

Figure 2: Command interpreter. A very simple interpreter is employed by the program. It requests a command input, tests the command for validity with a computed GO TO at line 780 to activate the appropriate command segment, invalid commands fall through the GO TO statement and lead to printing of a command list on the output display.

f COMMAND j

700

INPUT COMMAND

800

OUTPUT

COMMAND

LISTING

YES

760

INFORM USER

r APPROPRIATE COMMAND

One warp factor represents the length of one quadrant. It is possible to move very short distances by using warp factor values less than one. Every time you move to a new location, you will get what is known as a short range scan which is a printout of the quadrant you are currently in. The symbols used in the short range scan are:

Enterprise <*>

star *

Klingon +++

starbase >!< Figure 4 shows the actions which take place during the execution of this command.

Occasionally, after using enough warp factors to get you to who knows where, you will discover that you haven't gotten anywhere. This is because you have run into something, probably a star. Fortunately, your warp engines will always bring you to a screeching halt in time to prevent an accident. This is why it is a good idea to check your short range scan before laying out a

108

Figure 3: Course vector diagram. Numbers are used to determine the direction in which the Enterprise wili move, or a photon torpedo is fired. These numbers are reiated to the points of a compass as shown here; fractionai vaiues are used to generate points in between these major headings.

Listing J, continued:

5 -»

course, to make sure you have a clear path to your destination.

Command 1 will output a long range scan. A long range scan is a table containing information on the quadrants bordering the one you are in. It is arranged on a 3 by 3 grid, with your own quadrant being the one in the center. You are given a three digit number for each quadrant. The hundreds digit of this number is the number of Klingon ships in that quadrant. The tens digit is the number of starbases, and the ones digit is the number of stars. Be sure to remember that leading zeroes will be suppressed on the printout. Sometimes an entire row on the long range scan will be made up of zeroes. This represents the edge of the galaxy, the perimeter of your range. The warp engines will not permit you to enter this area. Instead, you will bounce off the edge.

Command 2 is the phaser firing section. You may destroy a Klingon ship by firing enough units of phaser power to deplete his shields. The question is, how many units are necessary to do this? One factor you must consider is the amount of energy he has in his deflector shields. For every unit of energy you hit him with, his shields drop a corresponding amount. Your distance from the Klingon also matters since the amount of energy that reaches him lessens with distance. Your sensors will tell you how successful you have been in damaging the Klingons. Your phaser fire is evenly divided

910 GOSUB 333 0

92 0 PRINT "TORPEDOES"** SPA< 4) **P

330 GOSUB 3330

940 PRINT "SHIELDS-; SPA(6);S

950 GOSUB 3330

960 PRINT "KLINGONS"; SPAC 5) ;K9

970 GOSUB 3330

980 PRINT

990 PRINT XS

30 OS RETURN

3010 PRINT "COMPUTER ACTIVE AND AWAITING COMMAND";

3020 INPUT A

3630 GOTO CA+1) OF 2280*3100*3310

304 0 PRINT "FUNCTIONS AVAILABLE FROM COMPUTER"

3650 PRINT - 0=DAMAGE REPORT"

3060 PRINT " 1» PHOTON TORPEDO DATA"

3070 PRINT " 2="SH0RT RANGE SCAN"

308 0 PRINT

309 0 GOTO 3010 3100 PRINT

31 10 FOR 1=1 TO 3 3120 IF KCI*3] <= 0 THEN 3200 3130 X=KtI*2J-S2 3140 Y»S1-KU*13

315 0 IF X-0 THEN 324 0

316 0 A«INT(((57.3*ATN(Y/X))/45* 1)* 100)/100 3170 IF X>0 AND Y< 0 THEN 3290 318 0 IF X<0 THEN 322 0 3190 PRINT -DIRECTION»-;A 3200 NEXT I 3210 GOTO 700 322 0 A=A+4 3230 GOTO 3190 3240 IF Y<0 THEN 32? 0 325 0 A-3 3260 GOTO 3190

327 0 A-7

328 0 GOTO 319 0

329 0 A= A+ 8 3300 GOTO 3190 3310 GOSUB 2600 3320 GOTO 700

3330 REM ***** OUTPUT QUADRANT *****

3340 Z*Z+I

3350 FOR 1=1 TO 8

3360 ZS»" <*>+ + + * >!<■

3370 PRINT ZJtQCZ*n«3+l*QCZ*13*3+3*;

338 0 NEXT I

339 0 IF Z» I OR 2-8 THEN 3410 3800 PRINT SPA<5>; 3511 0 RETURN

3420 REM ***** PRINTS DEVICE NAME *****

343 0 RESTORE 3440

3(140 DATA "WARP ENGI NES"* "SCANNERS"

3450 DATA "SHIELD CTRL "* "COMPUTER"

3460 FOR X=l TO Rl

3470 READ ZJ

3480 NEXT X

349 0 RETURN

350 0 REM **** PLACEMENT IN QUADRANT ARRAY *»** 3510 R1-FNAC8)

352 0 R2=FNAC8)

3530 IF QCR1*R2]#0 THEN 3510

354 0 RETURN

3550 PRINT LIN(l)*"YOUR RESIGNATION HAS BEEN *ACCEPT£D*"

3560 STOP

3570 PRINT -DO YOU NEED INSTRUCTIONS";

358 0 INPUT AS

3590 PRINT LINC5)

3500 IF AK1*|]#"Y' THEN 440

3510 PRINT SPAC5>;-<*> =ENTERPRISE"

362 0 PRINT SPA(5>;" * -STAR"

3630 PRINT SPA(5);" + + + =KLINGON"

3640 PRINT SPA(5>;">!< *STARBASE"

3650 PRINT LIN(2>

3560 PRINT "COMMAND 0*WARP ENGINES"

3670 PRINT "COURSE IS IN A CIRCULAR VECTOR AS SHOWN. "; TAB( SO); "4

'3680 PRINT "REAL VALUES MAY BE USED. FOR EXAMPLE* "J TAB( 51); "\ " /"

3690 PRINT "1.5 WOULD BE HALFWAY BETWEEN 1 AND 2. »J TAB( 52) i "\"/m

3700 PRINT TAB(48);-5 1"

37 10 PRINT "A 'WARP FACTOR' IS THE SIZE OF ONE QUADRANT. ■; TAB( 52);

3720 3730 3740 3750 3760 3770 378 0 3790 3100 3 10 320 3830 340 350 360 370 380 390 300 39 1 0 3520 330 340 359 960 370 380 39 0

PHASER BANKS"* "TORPEDO TUBES

PRINT TABC5I);"/ * \" PRINT TABC50);"6 7 §" PRINT "COMMAND 1=LQNG RANGE SCANPRINT "CODED IN THE FORM XXX* WHERE THE UNITS ARE THE NUMBERPRINT "OF STARS* TENS THE NUMBER OF STARBASES* AND HUNDREDS" PRINT "THE NUMBER OF KLINGONS." PRINT LIN(2)*"COMMAND 2-PHASERS"

PRINT "YOU MAY DESTROY THE KLINGON BY USING ENOUGH PHASERPRINT "POWER AS TO DEPLETE HIS SHIELDS. KEEP IN MIND THAT WHENPRINT "YOU FIRE AT HIM* HE GONNA DO IT TO YOU* TOO!" PRINT LIN<2)* "COMMAND 3»PHOTON TORPEDOESPRINT "COURSE IS SAME AS WITH WARP ENGINES. THE LIBRARYPRINT "COMPUTER CAN COMPUTE TRAJECTORY FOR YOU (OPTION I) " PRINT LINC 2)* "COMMAND 4»SHI ELDS"

PRINT "DEFINES THE AMOUNT OF ENERGY TO BE ASSIGNED TO SHI ELDS. ■ PRINT LIN< 2)* "COMMAND 5-LIBRARY COMPUTERPRINT " OPTION 0= DAMAGE REPORTPRINT " A STATE OF REPAIR LESS THAN ZERO INDICATES THATPRINT " THAT DEVICE IS TEMPORARILY DISABLED." PRINT " OPTION l»PHOTON TORPEDO DATAPRINT " GIVES DIRECTION TO ALL KLINGONS IN YOUR QUADRANT." PRINT " OPTION 2-SHORT RANGE SCAN"

PRINT " ALSO GIVEN AUTOMATICALLY AFTER SUCCESSFUL COMPLETION" PRINT " OF WARP ENGINE MANEUVERS."

PRINT LINC2), PRINT LINC6) GOTO 44 0 END

-COMMAND 6=RESI6NATI0N

109

f ENGINES J

690

INPUT COURSE

1030

1070

RANDOMLY

INFLICT

DAMAGE

1120

MOVE ENTERPRISE

1330

INCREMENT STARDATE

690

OUTPUT SHORT RANGE SCAN

-f COMMAND J

Figure 4: Engines and navigation service routine. This routine is used to set the Enterprises's course heading, speed (warp factor), move the Enterprise to its new position, and simulate Klingon actions with ran domiy in flic ted damages. Foilowing execution of this routine, the game normally returns to the command interpreter.

Figure 5: Phaser firing command service routine. The purpose of this routine is to fire the phaser, calculate damages to the Klingon ship (if any), and give the Klingon a chance to fire back with the effects of damage to the Enterprise computed.

fPHASERS J

-/ COMMAND J

1000

2470

GzD

690

OUTPUT SHORT RANGE SCAN

2470

YES

-f STOP J

f COMMAND J

INFORM USER

-/ COMMAND j

1660

(command j

INPUT AMOUNT OF ENERGY TO FIRE

-f COMMAND J

FIRE PHASERS

1770

f-f COMMAND J

2050

Trekkies Take Heart

Recent news stories took note of the unveiling of the first production NASA Space Shuttle at Rockwell international^ facilities in California. The impact of Star Trek is evident; The name of the ship is ''Enterprise/' (it is even complete with five general purpose but dumb, ie; voiceless, ship's computers and can't fly without them).

INFORM USER

2070

REMOVE KLINGONS FROM ARRAY

2150

KLINGONS

RETURN

FIRE

2440

2470

YES

-C STOP J

f COMMAND J

110

between ail of the Klingons in your quadrant. Thus, if you fire 600 units, and there are two Klingon ships, you are in effect firing 300 units at each one. Figure 5 shows the flowchart for the phaser firing sequence.

Command 3 is for firing the photon torpedoes. To fire torpedoes, you must first know the direction to your target. This, like the navigation course, is determined on the circular vector shown in figure 3. The library computer can compute the torpedo trajectory for you.

Often a star may be in your way, thus

Table 1: Some of the variables described by function. These variables have unique uses as described. Not all variables are listed in this table.

B3 C$

E K3

K9 N

P

S

S3

T TO

01,02

S1,S2 D(1)...D<6)

G(1,1)...G(8,8) Q(1,1)...Q(8,8)

K(1,1)...K(3,3)

K<l,1)

K(l,2)

K(l,3) FNA(X) FND(O)

The number of starbases in the current quadrant. String containing the current condition: red, green, yellow, or docked.

Amount of energy remaining. The number of Klingon battle cruisers in the current quadrant.

The total number of Klingon ships in the galaxy. Three digit number stating number of Klingons, starbases, and stars in quadrant. The number of photon torpedoes remaining. Units of energy currently assigned to shields. The number of stars in the current quadrant. The current stardate. The stardate on which the game began.

Specifies the X and Y coordinates of the current quadrant within the galaxy. Specifies the location of the Enterprise within the quadrant. Each element contains the state of repair for its respective device, (ie: D{3) contains data for device No. 3). Each element is a three digit number containing data on a single quadrant of the galaxy. Each element is a number 0 to 4, specifying what type of object is situated in that sector of the current quadrant. Contains information on the Klingons in the current quadrant:

The X coordinate of Klingon number I.

The Y coordinate of Klingon number I.

The shield power of Klingon number I.

Returns a random number in a form useful to the program. Returns the distance from the Enterprise to another Klingon.

preventing you from hitting your would-be victim. The only way around this, other than using phasers, which do not follow a predetermined course and hence are not stopped by stars and other obstacles, is to use a small warp factor and maneuver in on the Klingon. Figure 6 shows the sequence that takes place when the photon torpedo command is initiated.

Command 4 allows you to raise or lower the Enterprise's deflector shields. It is neces

INPUT

TORPEDO

TRAJECTORY

-f COMMAND J

FIRE TORPEDO

I950

2I80

INFORM USER TORPEDO MISSED

2060

INFORM USER

2I20

YES

INFORM USER

HIT STARBASE

2I50

C

Figure 6: Photon torpedo command service routine. This routine is entered when a photon torpedo is to be fired. It calculates the trajectory, examines the results for any Klingon hits, allows for Klingon return fire, then returns to the command routine if the Enterprise has survived.

2070

2090

2550

~\ ST0P J

2370

KLINGONS

RETURN FIRE

2440

YES

J

(command J

111

sary to be certain that your shields have sufficient energy before entering a combat area, because every time you fire at a Klingon, the Klingons fire back at you!

To clarify, you are subjected to Klingon phaser fire every time you use phasers or photon torpedoes. The amount of energy the Klingons hit you with depends on how far away they are. For every unit that

reaches you, your deflector shields drop a corresponding amount. If they drop to less than zero, you lose the game. You are given a short message within the short range scan every time your shields get too low. You are also given a condition yellow whenever you get precariously low on energy. The sequence for raising the shield energy is given in the flowchart of figure 7.

Listing 2: Sample outputs of the program in iisting 1.

TUN STTR

DD YOU NEED INSTRUCTI ONS?N

ENERGY TORPEDOES SHIELDS KLINGONS

2*1 13

COMMAND: ?5

COMPUTER ACTIVE AND AWAITING COMMAND?!

COMBAT AREA CONDITION RED

SHIELDS DANGEROUSLY LOW

COMMAND:?- 1 fcSET COURSE

STARDATE

3000

CONDITION

•RED*

ENERGY

30 0 G

TORPEDOES

15

SH I EL DS

0

KLINGONS

£6

* TORPEDO CTRL 5

^SHIELDS f*\

^LIBRARY COMPUTER / " \

6= RESIGNATION 6 7 8

DIRECTIQN= 7.99

D!RECTI0N= 7.74

□ RECTIQN= 7

COMMAND! ?3

TORPEDO COURSE C 1 -9>;?7

•••KLINGON DESTROYED*** 2 4 UNIT HIT UN ENTERPRISE

28 UNIT HIT ON ENTERPRISE

COMMAND:?!

0 : 2 : 5 :

0 :205 ; 5 ; 0 : 3 :202 :

COMMAND: ?0

COURSE < 1-9): ? D_ I

VlfiRF FACTOR C 0-8) I ?3

BIERGY AVAIL ABLE= 3000

NUMBER OF UNITS TO SHIELDS:? 50 0

COMMAND: ?5

COMPUTER ACTIVE AND AWAITING COMMAND?-!

FUNCTIONS AVAILABLE FROM COMPUTER

0*DAMAGE REPORT

1 = PHOTON TORPEDO DATA 2=SHORT RANGE SCAN

COMPUTER ACTIVE AND AWAITING COMMAND?!

ur.ECTIUN= ?-? DIRECTION- 7

COMM AN D: ? 3

TORPEDO COURSE Cl-9):?7

COMMAND:?!

: 2 05 : 4:103:

: 4 : 3 : 5 :

: 13 : 1 : 4 :

COMMAND: ?Q COURSE C 1-9) : ?6

VARF FACTOR < C-8) 1

: ? 1

SHU

KLIA

.DS

SOUS

12 23

•KLINGON DESTROYLL***

2 UNIT HIT ON ENTERPRISE

*COU

YOU CAN'T DESTROY STARS* SIlLY!

TORPEDO MISSED 22 UNIT HIT ON ENTERPRISE

COMMAND: ?2

KJERGY AVAIL ALL £= £500

NUMBER OF UNITS TO FIRE:?3 0 0 3 6 UNIT HIT ON KLINGON

13 UNIT HIT ON ENTERPRISE COMMAND: ?£

EJERGY AVAILABLE= 1700

NUMBER OF UNITS Tu FIRE:? 1000

KLINGONS

COMMAND: ?G

COURSE ( 1-9) : ?3

VARF FACTOR ( 0-8) : ?2

COMBAT AREA CONDITION RED

SHIELDS DANGEROUSLY LOW

COMMAND: ?£

BJERGY AVAIL A£t-E= 70 0

NUMBER OF UNITS TO F1HE:?4Q0 4 3 UNIT HIT ON KLINGON

•••KLINGON DESTROYED**** COMMAND: ? 1

Si 0 : 0

~0~:~ 5 t 1

COURSE ( 1-9): ?7

VftRP FACTOR C 0-8):?3

COMBAT AREA

CONDI TI UN RED

TORPEDOES

SHIELDS

KLINGONS

HJERGY AVAILABLE- 2989

NUMBER OF UNITS TO FIRE:? 1000

82 54

UNIT HIT ON KLINGON UNIT HIT ON KLINGON

20 UNIT HIT ON ENTERPRISE

•••THE ENTERPRISE HAS BEEN DESTROYED*** TIE FEDERATION WILL BE CONQUERED!!! EDNE

112

Command 5 allows the user access to the library computer which has three options specified by an integer between zero and two. If you enter an illegal option, such as a negative number, the computer will print a short list of commands.

Option 0 gives a damage report. The Enterprise may get damaged when you warp out at high speeds. When this occurs, you are informed as to which device has been affected. Extensive damage to a device may render it inoperable. In the damage report, each device is listed along with its respective state of repair. A state of repair less than zero indicates that the device is temporarily disabled. Repairs are made, albeit slowly, by onboard technicians, but a faster way is to dock with a starbase. Not only does this automatically repair your ship, but you are also resupplied with energy and photon torpedoes. An extra bonus: While docked, you are protected from Klingon attack by the starbase's shields.

Option 1 calculates the torpedo trajectory to all Klingons in your quadrant. Option 2 prints range scan. If you are docked with a starbase, it also replenishes your supplies.

f SHIELDS j

2200

PRINT

AVAILABLE

ENERGY

22IO

INPUT

ADDITIONAL SHIELD POWER

2260

RESET SHIELDS

-f COMMAND J

f COMIV

)

Figure 7: Shields service routine. This routine updates a power ievel for the Enterprises^ shields.

Command 6 indicates that you wish to resign. Other good ways to end the game prematurely are to torpedo a starbase, or allow yourself to run out of energy.

Conversion Notes

As everybody knows, the growth of the personal computing field has been constantly hampered by the problem of standards. This has been particularly bothersome in the software agenda, where there are said to be no fewer than forty different versions of BASIC floating around. Consequently, I thought it would be appropriate to comment on some of the difficulties one might encounter in the conversion process.

Many BASICs have explicit matrix manipulation features. In particular I used MAT . . . ZER extensively. This statement initializes all the elements of a specified matrix to zero. It also allows the programmer to redimension the matrix.

LIN(X) appears in several places within the program. LIN is an output control function similar to TAB, which generates X number of linefeeds every time it is encountered.

GO TO. . . OF is replaced by ON ... GO TO in many BASICs.

Substrings in the form X$(1,x) are replaced by the construct LEFT$(X$,x) in Altair BASIC. Also, Altair BASIC does not require that strings be dimensioned.

PRINT USING is used to format the long range scan. Output should appear in the following form: : xxx : yyy : zzz : The values of xxx, yyy, and zzz are the status reports concerning the number of Klingons, starbases and stars discussed under command 1.

The symbol # is used to express inequality within IF . . . THEN statements. Also, matrix subscripts are surrounded by brackets rather than parentheses. Near the beginning of the program, the sequence A=B=C=::. . . is used to initialize many variables to the same value. This may produce unpredictable results on some machines.

The memory requirement of this particular version of Star Trek is 10 K bytes, plus interpreter. The program itself is 9382 bytes long. If your computer has an integer variables option, by all means use it. It can save you over 300 bytes on the matrices alone. If you are cramped you can also delete the instructions from the program. To do this, simply delete statement 350 and lines 3570 through 3980."

Positively Baker Street

Here is the solution to the "Baker Street Irregular" which appeared on page 86 of the February 1977 BYTE.

■

ESESIE

1 t^j ffftffo

J J.L in e

M , , m lyj , _ , r T « „ E

m "- .

113

Photo 1: The typical board in a Digital Group kit comes in a sealed plastic bag with two compartments. One compartment contains the board and the second contains the necessary parts.

Steve Ciarcia

Box 582

Glastonbury CT 06033

Try This Computer on for Size

There are a number of fine microprocessor system kits available to the home computer enthusiast. One such system, which 1 just recently assembled, is the Digital Group 8080A. This microcomputer is marketed by the Digital Group in Denver CO. This concern, with Dr Robert Suding as its resident genius and designer, offers in my opinion the highest price performance of any home computer available. The Digital Group is somewhat unorthodox by not jumping on the bandwagon and being Altair bus compatible but their unit contains enough bells and whistles to placate even the most demanding computer owners.

This system, as is true of most others, has its good and bad points. I am an electrical engineer well versed in digital design and have been closely following the microcomputer scene since the advent of the MARK-8 in 1974. I have a Scelbi 8B and have helped friends build Altairs and IMSAls from kits and feel that I can be completely objective. It is of course extremely difficult to restrain laudatory comments when one is so well satisfied, but bear with me.

The Digital Group sells a basic computer system which can contain one of four processor chips: the Zilog Z-80; AMD 8080A; MOSTEK 6800; or a MOS Technology 6502. I chose the 8080A because of a combination

of price and software availability. The Digital Group System (DGS) is generally sold as a three board system with mother board. This three board microcomputer has the following functions and specifications.

Processor Board AMD9080A

2 K bytes programmable memory

and EROM bootstrap loader. Direct Memory Access (DMA) logic. 8 level hardware vectored interrupt. Buffered address and data bus lines. 16 bit (64 K) addressing capability. Input Output Board

Four 8 bit parallel input ports. Four 8 bit parallel latching output ports.

Full 16 bit port addressing. TV Readout and Cassette Interface Board Video Readout:

Software controlled cursor. 51 2 characters organized as 16 lines by 32 characters. 7 by 9 character matrix. FuU 128 ASCII character set. Upper and lower case alphabet. Math symbols. Special symbols. Greek alphabet.

114

Direct video output. Cassette Interface:

Uses standard cassette recorder. FSK recording technique. Wide shift Teletype frequencies. Operates at 1100 bps. Utilizes "software UART."

An additional 8 K programmable memory board is added to the three board set and is sold to make a four board set. The specs on the programmable memory are as follows:

8 K Static RAM Board

Uses 2102-1 parts with

500 ns access time. No wait states. Buffered address lines. Address decoding covers full

64 K range. Power consumption 2 A at 5 V.

There are many variations of the basic system as described, and this listing is only representative of their total offering. Interested parties should contact the Digital Group at POB 6528, Denver CO 80206.

As I mentioned previously, I had been following the DG since they entered the microcomputer scene. Their first offering was a simple 300 bps "el cheapo" cassette interface which met absolutely nobody's standard. While everyone was arguing Kansas

City and all the rest, I built this for $6 and had it operational in three hours. I have always been action oriented and all the talking in the world won't put your system on line. I have grown to expect and accept the unorthodox from the Digital Group.

Other manufacturers sell basic bare bones systems for prices starting around $600. For this price they contain a fancy case and front panel, gigantic overkill power supply, and a processor board with ancilliaries. There is no memory, IO, or mass storage capability: These are all extra cost options. Minimum capacity machine language and cassette storage system can approach $800 to $900. I affectionately refer to this nickel and diming as an "arm and a leg turnkey system."

The DGS is a profitmaking venture, I assure you; but it appears to have pricing and design philosophies which in my opinion better meet the needs and requirements of the knowledgeable experimenter.

When one buys a DGS three or four board system, you get Digital Group's version of the logically complete product: a system which in its basic price has no case, power supply or front panel. These are available from DG and can be purchased of course by the affluent or built from scratch by the frugal. Add a power supply, a video monitor salvaged from an old TV, a surplus

Photo 2: The author's Digital Group 8080 processor card. The actual processor is an AMD 9080A, one of the second sources of the original Intel 8080 design. The crystal which controls the processor clock is at the lower right, and the 2 K byte section of memory on the card is represented by the two rows of eight sockets at the left edge of the card. A UV erasable ROM chip (marked "80A " with a felt tip pen on the top edge at left of center) contains systems software which eliminates the need for a formal "blinkin' lights" front panel.

Photo 3: The author's Digital Group System 8 K byte memory card. The card contains 64 memory integrated circuits (in two arrayed segments) and in the center are various misceiianeous circuits used to interface the backplane bus of Digital Group system.

ASCII keyboard, and a decent cassette recorder; and you are in business with a complete functioning microcomputer.

I had been hearing this rhetoric and receiving DGS flyers for a while. Then I decided to take the plunge. I called DGS one morning in mid 1976 and ordered the four board 8080A system with standard mother board. Since this four board set contains 10 K bytes of programmable memory and is capable of supporting an Extended Tiny BASIC, I ordered the TBX software for $5. The total 10 K system as ordered was $645. Literature supplied by DGS quoted 30 day delivery but I had resigned myself to the possible two month wait that friends were experiencing with other companies. When the complete package arrived three weeks later I was ecstatic and set out immediately to the task of getting "on line."

The packing material, though sparse, was adequate; and, since there were no heavy components like transformers, its lack was inconsequential. Like any kit builder, I expected the first project would be to separate the pile of parts and boards and to sort components out among the respective boards. Anyone who has ever experienced sifting through a pile of resistors until their eyes cross can appreciate what I am saying. Fortunately this was unnecessary. Each board is packaged in a two compartment sealed plastic bag. One side contains the blank printed circuit board and the other

contains all the integrated circuits, sockets, and other components as seen in photo 1. When unpacking, two things are immediately apparent. The boards are top quality with plated through holes and there are no jumpers.

I searched through the box looking for the usual last minute revision sheets and tackons but there were none. This apparently was a final design with absolutely no "kluge rigging" necessary to make it work. The Digital Group flyers indicate they do not sell interim designs nor advertise anything for sale until it is available "off the shelf." From my experience, this appears to be the truth.

The ease of construction of this system is a function of the particular board being assembled. I'll cover each board separately, but a word of caution first. The Digital Group System is not and should not be considered in the same realm as a Heathkit or similar undertaking. Hardware documentation is adequate and descriptive but is not as detailed pictorially as a Heathkit. This is not a kit but rather an unassembled microcomputer. Its construction should be attempted by the experienced kit builder only. If necessary, build several difficult Heathkits first to gain, experience with electronics components and assembly. At the least, difficult assemblies should be purchased as fully assembled and tested units and the other cards carefully constructed.

116

Building the Processor Board

The processor board is of course the heart of the microcomputer. This card contains the microprocessor itself and supporting components. It is shown (after I assembled it) in photo 2. The Digital Group has sought to learn from the experiences of other manufacturers and builders and has obviously benefited. The most notable addition is the incorporation of integrated circuit sockets throughout. Even with the use of prime components, bad circuits are possible. The average hobbyist may have considerable experience doing the initial soldering, but unsoldering an integrated circuit is quite messy. Using sockets adds the capability of quickly changing a suspected bad component without either destroying the integrated circuit or the printed circuit board.

Significant effort and thought has been put into this microcomputer design as is evident in the system architecture of the processor card. The microprocessor is driven by a crystal controlled clock which exhibits none of the frequency instability of multivibrator controlled clocks. Crystals are currently used in most microprocessor systems for their "rock like" stability. In addition, there is 2 K of programmable memory on the board which can be selected to respond to any two consecutive 1 K positions in memory address spaces. For startup and checkout, this memory should be set for 0 to 2 K allowing the user to perform limited machine language programming without additional memory. I'll cover the procedure for checkout a bit later.

There are of course other goodies on this card. Direct Memory Access (DMA) and priority interrupt hardware is provided as a user option. The basic three and four board systems include test procedures for the interrupt request logic but DMA checkout is

Photo 4: The author's Digital Group System 10 card. This card interfaces to the system's bus, providing four para!lei output ports and four input ports. These ports are routed to the backplane where they communicate to the video displayf keyboard and cassette interfaces.

left for the brave of heart and is not addressed here. In addition to this circuitry, a 1702A EROM containing the tape cassette bootstrap loader is located in Page 0 of memory. When power is turned on, a power on reset signal initializes the system and reads in the operating system cassette. More on this later.

The Digital Group System bus structure is similar but differs in detail from that of the Altair. Robert Suding's publicized philosophy dictates an interchangeable processor capability which hopefully decreases the obsolescence of the total system. As new and more powerful microprocessors such as the Z-80 come on the market, a new processor card should be interchanged with the bus of the older unit while not affecting the rest of the system. To accomplish this goal, the Digital Group system uses unidirectional address and data buses as in the

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117

I I. •; /.'•

J* / H

I'M. Mm

f<*> ill ■ W

ffcoto 5: The cassette and CRT interface board. This board contains the video signai generation and audio processing circuits of the Digital Group System. [For more detailed descriptions, see the July and August 1976 issues of BYTE.]

Altair. Such a bus structure, as has often been seen in the marketplace, is easily adapted to any 8 bit processor. There is of course a basic disadvantage to owning a unique backplane pinout, that of having only a single source. Every microprocessor manufacturer knows that few designers will tie themselves to a single source part. That is the reason you see so many different companies producing 8080s. The Altair bus has been widely second sourced, which has led to some fierce competition resulting in modest benefits to the buyer. Obviously the small system owner does not have the same constraints as the high volume manufacturer but he should be aware of the lack of price competition and interchangeability when it comes to memory and IO card expansion. The Digital Group is apparently aware of their unique position and has sought to dispell concern by selling blank IO and 8 K memory boards at a very reasonable price. This allows the user to shop around for the best 2102-1 memory prices.

Since the DGS has no front panel, the processor card cannot be checked out easily by itself. But then no real functional test of a processor system as a whole can be easily performed with a front panel, either. The rest of the system must be constructed to perform the necessary diagnostics.

Assembling the Memory and IO Boards

Both the 8 K memory and parallel IO boards are constructed in a very straightforward manner. Again all integrated circuits are socketed and literature supplied is both

explicit and clear. The memory board (see photo 3) and components supplied to me contained premium grade AMD 2102-1 parts. With these parts no wait states are required and the processor runs at full rated speed.

The IO card which contains four parallel inputs and four latched parallel outputs must be set to the lowest order addresses when only one IO board is in the system. This is because the video display generator, keyboard and cassette interface are directly wired to IO ports on this card through the mother board. The ports are address selectable; but to utilize the DGS operating system software, the addresses must be set as described in the DGS write up. Additional memories or IO can have addresses to suit the user.

Assembling the Cassette and CRT Interface Board

This board is the external communications medium of the Digital Group microcomputer. Since the DGS has no front panel, it is solely dependent upon a video based operating system utilizing the video display generator interface and a television monitor, or modified television. The software for such an operating system is about 1.5 K and cannot be entered except through the cassette interface. I should clarify one thing though. The DGS which I purchased is quite amenable to front panel hookup. The three and four board units sold by the Digital Group do not incorporate front panels but they do provide a design for one. Obviously,

118

if a user builds a DG system and both his processor and video display sections fail to function properly, he is dead in the water and would have to build the front panel. The design is neat and functional and plugs into any spare memory card slot. If, on the other hand, the user is thoroughly frustrated, suspect boards can be returned to DG for troubleshooting according to a price schedule supplied with the unit.

Now that you know how to get yourself out of the hole if it happens, I'll explain the proper method of digging.

The CRT and cassette interface sections are assembled using the same methodical approach as the other boards. The literature is very good in this respect. The problems come in calibration. The CRT is fairly straightforward, it either works or it doesn't. There are no adjustments. This section, when completed, is plugged into the mother board, attached to a monitor, jumpered as per the testing procedure, and powered up. If it works the screen will be immediately filled with 512 random characters. These characters include upper and lower case alpha symbols, and Greek lettering. When this works you are half done with the check out of the card.

Being half done in this case is not nearly enough. The assembly of the cassette interface is simply a matter of following directions but calibrating it is a bit of a task. There are operating system options which allow the computer to function as a frequency counter, but that is a little further downstream. To properly adjust the cassette interface, a scope, a frequency counter, an accurate DC voltmeter or DVM and a variable frequency oscillator arc required. I fortunately have all this equipment, but not everyone's spouse is as understanding as mine. The frequency source is set to 1 V p to p at 2125 Hz and applied to the inter

it Opt ton

OP 8YSTEX

1 REBD Cossatta

Z WRITE Cassetta

3 TV Storage Oump

4 Keyboard Program

5 Interrupt Tomtor

6 Hamory Taster

face input, simulating the tape recorder output. Using a scope to determine the point of peak response, the active filters are adjusted correspondingly. This procedure is repeated for 2975 Hz, Next the comparator which detects whether the input frequency is at a mark or zero is adjusted to switch cleanly as the frequency source sweeps between the two valves. That takes care of the receiver sections.

The FSK (frequency shift keyed) modulator is a single VCO (voltage controlled oscillator) chip which switches between two frequency values corresponding to TTL one or zero inputs. In initial checkout, a voltage (3.5 V) simulating a TTL level one is applied to the control line of the oscillator and the output is adjusted to 2125 Hz. The control line is then grounded and the output adjusted to 2975 Hz. If this can be accomplished satisfactorily, you're in business.

System Checkout

When all of the cards are assembled, and the solder splashes cleaned off, take one last look at each card. Remember, this is the smoke test.

Attach the power supply to the mother board and with no boards inserted and the power on, check that the proper voltages are present. Shut off the supply and insert the

Photo 6: When you get this far, you know your Digital Group System has arrived in the land of the living.

COMPUTER

T.V. CAMERA & DISPLAY INTERFACES FOR ALTAIR/IMSAI

• PLAY GAMES & LET YOUR COMPUTER SEE THE BOARD

•TEACH YOUR COMPUTER TO READ, DO SURVEILLANCE, ETC.

• LET YOUR COMPUTER MAKE DECISIONS BASED ON VISUAL INPUT

INTERFACE 1 V. Camera to Computer

INTERFACE II Computer to Monitor

240

215

64

120 107

16 to 64

5

Maximum Vertical Resolution Maximum Horizontal Resolution Grey Scale Resolution Maximum Conversion Time (Sec)

Any T.V. Camera with external sync, input can be used. Memory requirements4K to 64KRAM.INTERFACE UhComputer to Oscilloscope - 4096 points are displayable in any programmable array. Includes 4K 450ns static RAM usable by Oscilloscope or Computer. All equipment fully assembled and documented. Allow up to 90 days for delivery.

Ma.lchecksor ENVIROMENTAL INTERFACES n .^-^ « <„

money orders to 3207 Meadowbrook Blvd. Cleveland, Ohio 44118 (216)371-8482

'DINTERFACEI

lO INTERFACE I and T.V. Camera

I DINTERFACE II (excludes monitor)

'DINTERFACE III and RAM

I D12" T.V./MONITOR COMBINATION

iDSEND MORE INFO.

Enclosed is my check/money order for:$

$295 595 245 495 150

Name: _ Address: City:

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Ohio residents please add 5.5% sales tax, thank you.

119

processor, 10 and CRT cards. Cross your fingers and turn on the power. If all works correctly, the screen will display: "READ 8080 INITIALIZE CASSETTE". Successfully accomplishing this means that the processor is operating correctly, the CRT board works fine and at least part of the 10 board is functioning.

The acid test is loading the operating system via the cassette interface. (To facilitate this endeavor and add more ease of operation, a Reset/Run button should be wired to the mother board as described in the DG literature.) With this message present on the screen, insert the 8080 operating system cassette and hit the play button. Adjust the output level to be about 1 V p to p and soon a leader tone should be heard. No change should appear on the screen. Immediately following the tone will be the asynchronous data at 1100 bps. Proper reception of this data will be evident on the video display. As each byte of data is processed and loaded into memory, it is read from memory to verify that it got there. If it loaded correctly, a number corresponding to the high order digit of the octal page address of this byte location is printed on the screen. With 256 bytes per page, there will be 256 number 1s, 256 number 2s, etc, until the tape is loaded. Should the memory

Photo 7: A view of Steve's assembled Digital Group System.[When a party from the BYTE office stopped by at Steve's basement laboratory in Connecticut on the way back from Atlantic City last fall, we found his system up and running as pictured here, with his older Scelbi 8B computer acting as a slave peripheral processor to control the vector graphics output device described on page 78 of the November 1976 BYTE. Steve cooked an excellent Quiche Lorraine for dinner that night while Dan Fylstra and I explored a game of KINGDOM running in Tiny BASIC . . . CH ]

check signify a bad byte, a period (".") will be displayed instead of the octal number. It's a good idea to watch the screen while the cassette is being read.

If the cassette was read in properly, the computer will display the operating system options on the screen as in photo 6. If not, try again. Be careful to watch that there are no numbers, signifying received data bytes, on the screen prior to the playback of the actual data on the tape. Should this occur due to a noise glitch, hit the reset, and it will clear this problem.

The DGS operating system requires that alphanumeric information be input on a parallel 8 bit input port in the form of ASCII. Ail this means is that you need a keyboard. The ASCII is 7 bits of the input port and the eighth bit corresponds to the key pressed or strobe signal. The operating system scans this bit looking for a transition from a zero to a one so therefore it must be a positive going strobe (TTL level) with a minimum duration of 50 us. I have a surplus Sanders Associates 720 keyboard which a lot of people have. This keyboard has a 5 us negative going strobe though and must be modified by adding a oneshot such as a 74121 to it. Since the whole keyboard runs on 5 V, this is an easy conversion and the keyboard is an exceptional buy. With keyboard and monitor, the system is totally operational. If you were able to get the operating system option list which appears in photo 6, you are ready to go. Hit 3 and the screen displays the contents of all the registers and flags. Hit space and you'll start to page through memory displaying all memory contents. Return to the operating system and hit option 4 and the keyboard can be used to enter octal machine language code anywhere the user desires. The complete explanation is included with operating system tape.

Where the Digital Group System really shines is the cheap software and system simplicity. Add the 8 K memory board, set the address for 0 to 8 K and reset the processor 2 K memory to occupy 8 K to 10 K and we are ready to run Extended Tiny BASIC.

With 10 K of memory installed, turn the system on and start the 10 K Tiny BASIC tape as you would the operating system tape. After a few minutes the tape will have been read and the system will display the Tiny BASIC options:

TINY BASIC

1. READ BASIC PROGRAM

2. WRITE BASIC PROGRAM

3. DISPLAY COMMANDS

120

4. DISPLAY ERROR CODES

5. CONTINUE PROGRAMMING

6. TINY BASIC

With these options, an Extended Tiny BASIC, created by Dick Whipple and John Arnold and described in the January 1976 issue of Dr Dobb's Journal of Computer Calisthenics and Orthodontia, is ready to go. Buy a couple of simple programs such as Blackjack, Bantum and others from the Digital Group Software Systems, and you can utilize the computer immediately to entertain the whole family or bone up on Tiny BASIC and write your own programs.

Observations and Criticisms

As stated earlier, it is my opinion that the Digital Group System is one of the best offerings on the small systems market today. But as previously mentioned, anyone not having the proper equipment should not attempt to assemble the CRT and audio cassette interface. After receiving my system, I was up and running with the 2 K processor card memory with two evenings' work. Since I had the equipment and am very receptive to logical well written instructions, I had no troubles. My cassette interface didn't work at first, and I discovered that it was because of insufficient tape recorder bandpass. I had hoped to use the same el cheapo recorder that I used for my previous 300 bps interface, but no way. I rushed out and spent a whopping $39 for a new one from J C Penney which had been suggested by another Digital Group System owner. The first time I hit play, it worked perfectly. Since that time, I have discovered that the cassette interface is sensitive to both volume and tone settings during playback. This is probably only a function of the tape recorder I own and is not necessarily indicative of a general problem. Using a quality cassette recorder of the type suggested by the Digital Group should eliminate any playback problems.

Recording a program on tape is simply a matter of choosing the correct operating system option but getting accurate mark and zero frequencies may require minor tweeking. There appears to be some shift in the output frequencies from the time of the static calibration and actual dynamic operation. This is obviously due to the fact that 3.5 VDC and 0 V are not the actual TTL levels applied to the voltage controlled oscillator. A VCO is an analog device and not all TTL chips are exactly alike. After reading in the operating system tape I

Continued on page 129

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121

Multiplex Your Digital LED Displays

James Hogenson

Box 295

Halstad MN 56548

Digital LED displays were once a novelty t y the hobbyist, a luxury found in expensive lab equipment. They are now a household word and a useful tool for the digital experimenter. A digital LED display can be used as the readout for almost any test instrument. A programmable LED display can be used as a computer output. A digital

LED display is a handy replacement for the binary lights on a computer control panel. If you have been thinking about using an LED display for any of these or other reasons, this article may save you some time, money, and power.

There are two methods which may be used to drive an LED display. The direct

Figure J: Circuit diagram of a simple multiplexed S digit display for BCD or octal data. The printed circuit layout of this version is dep ic ted in figure 3. Figure 5 shows the printed circuit used to mount the displays.

Integrated Circuit Summary List

POWER

PINS

Type

+ 5 V

GND

IC1

7493

5

10

IC2

74151

16

8

IC3

74151

16

8

IC4

74151

16

8

IC5

74151

16

8

IC6

7448

16

8

IC7

75451

8

4

IC8

75451

8

4

IC9

75451

8

4

IC10

75451

8

4

IC11

74155

16

8

IC12

555

See figure 1

+ 5V A

g f e d c b a TO SEGMENT LINES

o a o o o o o OF ALL 6 LED DISPLAYS

NOTE: 8 MAN 4 or DL704 seven segment LED displays are required.

DIGIT DRIVES TO COMMON CATHODES OF DIGITS 0 TO 7 X7 X6 X5 X4 X3 X2

I I I I I I I f

12 13 14 15 I 2 3 4 DDDDDDDD 8 7 6 5 4 3 2 I

cccccccc

8 7 6 5 4 3 2 I

DATA INPUTS FROM PARALLEL OUTPUT PORT

122

power configuration uses one 7 segment driver for each 7 segment LED in the display. Constant power is supplied to all digits. The multiplexed configuration uses only one 7 segment driver for several digits. Power is supplied to only one digit at a time, but is switched at a high rate so all digits appear to be on constantly. Since only one digit is powered at any given time, a certain amount of power is saved. This principle is widely used in electronic calculators.

The circuit of figure 1 is the driver circuit for an 8 digit multiplexed LED display. This circuit will display 8 digits of parallel BCD

data. All data inputs are connected to a multiplexer. There is one 8 channel multiplexer for each of the 4 data input bits. The least significant bit of each digit is connected to an input of IC2; the most significant bit of each digit is connected to an input of 1C5, etc. The multiplexers and demultiplexer are addressed by the 7493 counter which is incremented at approximately 4 kHz by the 555 oscillator. IC11 is connected for 3 to 8 line demultiplexing. When the selected output line of the demultiplexer goes to a low state, one of the peripheral interface gates is enabled. IC7 through 1C10 are dual peri

Integrated Circi

lit Summary List

POWER

PINS

Type

+5 V

GND

IC1

555

See figure 2

IC2

74123

16

8

IC3

74193

16

8

IC4

7489

16

8

IC5

7404

14

7

IC6

7448

16

8

IC7

75451

8

4

IC8

75451

8

4

IC9

75451

8

4

IC10

75451

8

4

1011

75451

8

4

IC12

75451

8

4

IC13

75451

8

4

IC14

75451

8

4

IC15

74154

24

12

Figure 2: Circuit diagram of a digit-serial multiplexed 16 digit display with memory. The printed circuit layout of this version is depicted in figure 4. Figure 5 shows the printed circuit (two copies required) used to mount the displays.

NOTE: 16 MAN 4 or DL704 seven segment LED displays are required.

O

IC9

754 5 I

ice

7545I

ICIO 7545I

ICI2 754 51

ni

ICI4 7545I

ICll 7545I

FTs

ICI3 7545I

• ,

2

F7 77 77 77 77 ■■ 77 Tr 71

XI5 XI4 XI3 XI2 XII XI0 X9 X8 X7 X6 X5 X4 X3 X2

DIGIT DRIVES TO COMMON CATHODES OF DIGITS 0 TO 15

ICI5

74154

DIGIT SELECT

3 XI xo

123

Figure 3a: Printed circuit pattern (foil side) of the 8 digit display circuit.

pheral interface gates. Each gate is capable of sinking a current of up to 300 mA. When a digit is selected, the interface gate provides a ground path for the common cathode of the 7 segment LED. Only the LED whose

Photo J: A 16 digit BCD assembly constructed using the circuit of figure 2} with the printed circuit layouts of figures 3 and 5. The 16 digit memory display requires two copies of the LED mounting board, with jumpers connecting the segment lines from one board to the next. Power, data and address inputs are shown trailing away at the bottom.

cathode is grounded will light up. Although the same data will be present at all digits, the data will be displayed by only one digit. By changing the data present and switching the enabled digit, each digit will display its own data. A 7448 decoder/driver converts the BCD data to a 7 segment code and drives the individual segments of the LEDs. The segments of all 8 digits in the display are connected in parallel.

The circuit of figure 2 is a 16 digit programmable display. This circuit will memorize and display the data presented at its inputs one digit at a time. The size of the demultiplexer and the number of peripheral interface gates is doubled, since the programmable display has 16 digits. The input multiplexer is replaced by a memory which is loaded digit by digit. The 7489 TTL RAM, IC4, is very conveniently arranged for a 16 digit BCD memory. The RAM outputs are, however, inverted open collector outputs, so pullup resistors and inverters (IC5b to IC5e) are needed.

The counter used is a 74193 presettable binary counter, IC3. A 555 oscillator (IC1) drives the counter at 4 kHz. A digit is selected for programming by setting the memory address at the inputs of the counter. An external clock pulse at the clock input will program that digit. It is assumed the external clock pulse will be at least 200 ns. When the clock pulse input line goes low,

124

Figure 3b: Printed circuit component side map of the 8 digit display. See figure I for identification of components. Jumper wires are shown as dotted lines in the overlay.

SEG. DRIVE OUTPUTS TO DISPLAY BOARD(S)

fg abode

DIGIT DRIVE OUTPUTS X4 X5 X7 X2 X XO

+5V GMD

the counter will be disabled and the address on the counter inputs will appear at the outputs addressing the memory. IC2 provides a 60 ns delay, then a 60 ns pulse which writes the data at the memory data inputs into the memory location addressed. When the clock line returns to the high state, the counter will resume counting. The counter sequentially addresses the BCD data stored in the memory while it selects and enables the appropriate digit in the display.

Single layer printed circuit patterns are provided for readers who make their own boards. The inputs on the simple multiplexed driver board (figure 1 schematic, figure 3 printed circuit layout) are connected as follows: Bit 0 of the first digit to input A0, bit 1 to input BO, bit 2 to input CO, bit 3 to input DO, bit 0 of the second digit to input A1, bit 1 to input B1, etc. The segment outputs (a to g) should be connected to the display board (see figure 5b) at the pads provided on either end of the board. The digit (common cathode) driver outputs (XO to X7) should be connected to pin 4 of their respective digits.

Output connections for the 16 digit programmable display driver board (figure 2 schematic, figure 4 printed circuit layout) are the same as for the self scanning board. Referring to the component placement diagram, connect the BCD data input directly to the Dq, D^, D2, and D^ lines of IC4. The

riiHft ^liiiiii ^jtj^fr #MHm ' * v* l^^tf gH|^ ^u^^u ^xU2j» ^n^* 4MIM jm^i. 't «*^^> ^^^^

f mm m| >«B mm mmtfm*.

The Tarbell Cassette Interface

• Plugs directly into your IMS AI or ALT AIR

• Fastest transfer rate: 187 (standard) to 540 bytes/second

• Extremely Reliable—Phase encoded (self-clocking)

• 4 Extra Status Lines, 4 Extra Control Lines

• 25-page manual included

• Device Code Selectable by DIP-switch

• Capable of Generating BYTE/LANCASTER tapes also.

• No modification required on audio cassette recorder

• Complete kit $120, Assembled $175, Manual $4

TARBELL ELECTRONICS

144 Miraleste Drive #106, Miraleste, Calif. 90732 (213)832-0182 California residents please add 6% sales tax

125

Figure 4a: Printed circuit pattern (foii side) of the 16 digit memory dispiay circuit.

digit address input lines are connected to IC3 inputs A, B, C and D. To program the display, set the desired BCD value at the BCD inputs, select the desired digit with address lines AO to A3, and bring the clock input to the low state for a minimum of 200 ns. The first digit is selected by setting a binary 0 at the address input; digit number 4 is selected by setting a binary 3 at the address input, etc.

Any 7 segment common cathode LED may be used with this display. MAN 4 or DL 704 LEDs work well, wired up using the display card of figure 5. The use of the peripheral interface gates means that a single 5 volt power supply will be adequate without any extra LED driver circuitry. The entire display (either one) will draw 300 to 400 mA.

The 8 digit multiplexed display may

Figure 5a: Printed circuit pattern (foii side) of an 8 digit 7 segment LED assembly used with the display circuits.

126

PRIME RADIX

M*

o^

<&>

*$&

iTM

WE DO IT WITH MIRRORS!

(and some very sophisticated state-of-the-art memory design)

You've probably imagined that someday you'd like to own a computer system with a full complement of memory:

65,536 BYTES

Your dream can be a reality with the Prime Radix Corporation's 64Ktm memory system at a very cost-effective price. And because it is a standalone memory system, you've got the advantage of greater flexibility not ordinarily available from add-in memory. Some of the features are:

• The 64Ktm is fully buffered, presenting one TTL load to the memory bus.

• The 64Ktm is digital group bus and ALTAIRtm bus compatible When ordering, you must specify the bus

architecture. A plugcard and cable will be furnished for the particular bus architecture you specify.

• The minimum complement of memory is 40K BYTES, with starting address locations at OK, 8K, 16K, or 24K.

• The 64Ktm comes assembled and tested with its own power supply, attractively housed in an aluminum cabinet, ready to plug into your system.

• Psuedo-static operation: on board refresh clock-generator provides processor independent refresh with no wait states. The 300NS worst case access time enhances high speed operation.

• Power/fail detection circuitry and battery backup will provide non-volatile memory (batteries are optional at extra cost).

LIST PRICE IS AS FOLLOWS:

40K 48K 56K 64K

$1490.00 $1580.00 $1670.00 $1750.00

We are offering a special introductory ten percent discount off list price on all orders received on or before February 28,1977. Delivery will be made in the same sequence as orders are received. Please allow 3 to 6 weeks for delivery. Mastercharge and BankAmericard are accepted.

PRIME RADIX tPO Box 11245 • Denver Colorado 80211 • (303) 433-5630 or 573-5942

1

PRIME RADIX

COMPUTER SYNTHESIS

□ DIGITAL GROUP BUS

□ ALTAIRtm BUS

□ 64K @ $1750.00

□ 56K @ $1670.00

Make checks or money orders payable to:

PRIME RADIX. INC P.O. Box 11245 Denver. Colorado 80211 (303) 433-5630 or 573-5942

Print Name

Address

City

State

Zip

□ 48K @ $1580.00

□ 40K @ $1490.00

D Check or MO. enclosed

□ Charge BAC D Charge MC

(Please No C.O.D/s or P.O.'s)

Credit Card Number

4 Numbers Above Name (MC)Good Thru

Signature

j

127

Figure 4b: Printed circuit component side map of the 16 digit display. See figure 2 for identification of components, jumper wires are shown as dotted lines in the overlay.

+ 5V

CLOCK ADDRESS

DATA

GND I

AIA3A2AO Dl DO D3D2*

X5 (TYPICAL DIGIT DRIVE OUTPUT)

edcbagf

SEG. DRIVE OUTPUTS TO DISPLAY BOARD(S)

easily be used to replace the binary lights on a computer as an octal display. This display board is also a handy readout for any number of homebrewed instruments.

The programmable display may be used as a computer output. Connect the address and data inputs of the board to the 8 bits of

an output port. Connect the clock pulse input to the computer's output strobe line. Remember to program the computer to include the correct digit address in each data output. For use with hexadecimal data, use a substitute for the 7448 which decodes hexadecimal 7 segment patterns."

Figure 5b: Printed circuit component side map of the display matrix. The LED parts are MAN 4 or DL 704 seven segment displays or their equivalents.

SEG.

DRIVE

INPUTS

X7

L E D

X7

L E D

L E D

^7

L E D

DIGIT DRIVE TERMINAL

"C7

L

"E

0

TZ7

L E D

f° SEG. b DRIVE (TO h NEXT BOARD)

128

Continued from page 121

recommend that a short program be written to cycle the cassette output between a one and zero every few seconds. Connect a frequency counter to the output and readjust the mark and space pots to the correct specifications. I also noticed that variations in power supply voltages from one time to the next can adversely shift this frequency. Having an adequate well designed power supply will limit variabilities even as more memory is added. My 10 K system. draws approximately 4.4 A at 5 V and with 1 8 K on it; it now takes 5.7 A.

The last comment is no Digital Group problem, but rather mine. I assembled the 10 K memory board as instructed, plugged it into the system and ran the DGS memory test program for a couple of hours. It all checked out fine, but when I tried to read any program which occupied 10 K of memory (2 K worked fine) it bombed out. Since the memory test program said the memory was fine, I was led to suspect the 10 K BASIC tape. 1 shipped that tape off to a friend to try it on his DG system and contacted the Digital Group software people for a new tape. Within five days I had both a new tape from DG and confirmation from my friend that I had a problem because the tape was OK. But the memory test said the memory was OK! Well, don't believe it! In the process of removing and checking each 2102 on my 8008 system I found an IC with a pin bent under it. Straightening this pin and reinserting the 2102 was all that was needed, and the Tiny BASIC read and executed perfectly. Be careful of memory test programs.

In conclusion, my experiences with the Digital Group 8080A System have been gratifying. My system worked with no major problems, and any intelligent user either constructing the computer in whole or part should expect the same. The fact that I now have an operational microcomputer has caused a slight problem, though. 1 never get to use it! I seem to continually have people from my office over in the evenings programming one thing or another. In fact, I had to add another 8 K this week to allow more Tiny BASIC programming space for one guy who is writing a statistical program which he hopes will help him win at jai-alai. I suggest that if you get one of these small computers, just walk around with a pleasant pregnant smile, but for heaven's sake don't tell anyone that it really works!"

[Watch for Steve's humorous account of jai-alai in April's BYTE.]

$795

ECONOMY

TERMINALS ANNOUNCES: AN INTRODUCTORY OFFER ON THE ET1 CRT TERMINAL

24 x 80 display of the 64 uppercase ASCII characters

12" Industrial 15 Mhz monitor with anti-glaire screen and filter

• 90-day warranty (parts and labor. F.O.B. factory)

• 96-hour elevated-temperature operating test on each ET1 before shipping

» RS-232 and 20 ma interface

> LF, CR. BS, Local, Rubout Break, Home Clear, Tab*, Remote Cursor Placement*, and Scroll* functions with special function keys

• Sixteen switchable baud rates to 19.200

• Odd. even and mark parity with one or two stop bits Microprocessor Based, with 63-key keyboard

* These functions vary with model selected.

PLEASE CALL OR WRITE FOR MORE INFORMATION. THIS OFFER EXPIRES 30 APRIL 1977.

ECONOMY TERMINALS

Box 12261

Minneapolis, Minn. 55412

(612) 522-1076

MORE POWER TO YOURALTAIR*

12 AMPS @ 8v. (nominal) 2 AMPS ® ±16v.

At any line voltage from:

90 to 140 volts.

Installs easily inside any Altair* 8800 or 8800a.

Over voltage and over current protected. Conservatively designed and specified.

only $90.00

postpaid in the U.S.A. California residents add

master charge

^^^^** $5.40 sales tax.

PARASITIC ENGINEERING

PO BOX 6314

ALBANY CA 94706

* Altair is a trademark of MITS Inc.

129

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130

PAPERBYTES ™ Test

As noted in last month's BYTE, page 1 21, we had intended to have an extended text included in the magazine for February. The text got delayed, due to a combination of human, weather and Murphy's Law Factors. This month, it arrives at the printing presses for publication.

This text is an extended set of ASCII encoded English language words. The bit level format is format 3 (compressed ratio recording) as described in previous articles on the subject in BYTE November 1976, page 10, and BYTE December 1976, page 12. In this format, the width of the bars and spaces are encoded as follows: space = 1 unit width; zero bit = 1 unit width bar; one bit = 2 unit width bar. The frame format begins with an ASCII SYN (10010110) character extended to 8 bits with a high order 1 bit. The frame continues with 8 bits of check sum, 8 bits of line identification, and 8 bits of byte count. The byte count sets the number of data bytes which follow the header.

Add Some Zest by Making a Contest

Rather than just print another test, we decided to make this text sufficiently complex to warrant making a small contest out of it. Within the frame format we have encoded the plain text of ASCII upper and lower case characters (plus line control) defining Walter Banks' parody of a famous poem dealing with mythical critters and strife and conquests. Lewis Carroll purists will object to the arbitrary and incomprehensible semantic transformations made on the arbitrary and incomprehensible semantics of the original, but the necessities of making a contest required uniqueness: This version has never been published before and it is completely different at the detail level. All contests have ground rules, and here are the ones which apply to the first (and probably only) PAPERBYTES Contest:

• Entries must be received in our office by March 31 1977. They should be addressed:

BYTE magazine

Attention: PAPERBYTES Contest

70 Main St

Peterborough NH 03458

ACT-1

MICRO-TERM INC.

$525 complete with high resolution 9" monitor • $400 without monitor INCLUDED FEATURES:

• Underline Cursor

• RS232C or Current Loop

• All oscillators (horiz., vert., baud rate, and dot size) are crystal controlled

• 64 characters by 16 lines

• Auto Scrolling

• Data Rates of 110, 300, 600, 1200, 2400, 4800, and 9600 baud are jumper selectable

The ACT-I is a complete teletype replacement compatible with any processor which supports a serial I/O port. Completely assembled and dynamically tested. Prices FOB St. Louis Mastercharge and BankAmericard

THE AFFORDABLE CRT TERMINAL

MICRO-TERM INC. P.O. BOX 9387 ST. LOUIS, MO. 63117 (314) 645-3656

MULLEN COMPUTER BOARDS

BOX 6214 ■ HAYWARD, CA. 94545

N M.1AIK/IMIAI C

D NEW FOR TROUBLESHOOTING O

E AND DEVELOPMENT: A SUPER M EXTENDER BOARD FOR THE lII _^S lOO BUSS. W

■^ •Built in, 3 LED TTL logic probe Ak.

• Jumper links in power lines for easy I

B current measurement and fusing n

•Edge connector label identifies all pins ■

©•Outstanding instructions Jq

• Full width card; gold connector teeth ■

jtk AAT YOUR LOCAL COMPUTER mr

*^^^ •STORES, OR ORDER BY MAIL. [

RD MI: *?§

131

Personal Computing Goes National

It's happening at the Dallas Convention Center during the 1977 NCC, June 13-16

w w w w

W%

The 1977 National Computer Conference will be the year's largest gathering of data processing users, computer professionals and computer nobbyists. More than 25,000 people are expected to gather in Dallas for a conference program of more than 100 sessions and the year's largest display of computer hardware, software, systems and services — plus the first annual National Programming Contest and a series of outstanding Professional Seminars.

Specially featured will be the first NCC Personal Computing Fair & Expostion, comprising a Personal Computing Fair, papers and panels, club congress, headquarters hotel and product exhibits by leading manufacturers.

Entry Deadline Coming Fast

Personal Computing Fair entries must be non-commercial personal or groupowned small computing systems. They may feature hardware and/or software implementations, games, recreation, music, art, amateur radio, scientific, miscellaneous and general applications. Prizes and awards will be given in all categories.

Working systems are desired, although projects that might not lend themselves to display at the fair might be illustrated audio/visually if the judges believe the project is acceptable otherwise. NCC will provide at no charge the booth space, a sign, coordinated furnishings, power and lighting. Accepted entrants will earn free full conference registration (except for the Proceedings).

For information, write or call Ric Martin, Personal Computing Fair chairman, c/o The Micro Store, 634 S. Central Xwy., Richardson, Tx. 75080, 214/231-1096, To enter, send him a concise, one-page, double-spaced description of your system, with your name and home and business addresses and telephone numbers.

Entry Deadline Is March 15 Acceptance Announced By April 15

it •

1977 NATIONAL COMPUTER CONFERENCE

Dallas Convention Center • June 13-16

• Each entry should contain a stamped self addressed envelope (as well as redundant identification of the contestant) in the event materials are not used by our office in the publication.

• Each entry must contain the completely decoded text, either as a printed text listing (upper and lower case) or as a hexadecimal absolute data listing with one line per line of bars. Handtyped listings are fine, if you don't have a hard copy device.

• Each entry must be accompanied by a complete and detailed technical description of the system used to decode the text. Hand decoding is not an acceptable method. Brownie points in the judgment of entries will go to the least expensive systems (other things being equal).

While it is not necessary to treat entries as a formal technical article submission, winners and runnersup in the competition may be published with payment at our current rate for highly desired technical materials.

The Prize?

A check for $100 will be the bonus for the winning entry in this contest, as judged by BYTE's editor Carl Helmers based upon materials submitted.

A Note About Formats,

Coming PAPERBYTES Items, etc.

In this sample text, we do not provide the equivalent human readable form of materials. This is due to the nature of this month's test which is being treated as a contest. The arrow identifies the beginning of the text.

Normal practice when publishing programs in BYTE is expected to include printing of a complete hexadecimal object text for programs as a confirmation of the bar coded machine readable texts. Production problems notwithstanding, the first program we expect to print in this form will appear as bar codes in the May 1977 BYTE in the second part of Jack Emmerichs' article on his 'Tiny Assembler" for the Motorola 6800. We've been using Jack's assembler (we = Walter Banks at the University of Waterloo, Carl Helmers at BYTE, Chuck Adams at Texas A&M University) since late in 1976. Also planned for future release in this form are additional

LET YOUR COMPUTER XPRES ITSELF!

Your computer can control lights, burglar alarms, Hi-Ft's, PHASORS; practically anything if properly interfaced.

XPRES is a complete interface system. ONE EIGHT BIT PORT CONTROLS 128 SEPARATE DEVICES. Connect to Imsai, Altair, or SVVTPC; any processor with an eight bit port.

IMB-01 system mother board, holds five interface boards, complete with connectors,

KIT $28.00

IFB-01 interface board, controls two 115 VAC 300 watt circuits. Optically isolated.

KIT $38.00

IFB-04 interface board, controls 4 small signal AC/DC circuits with reed relays.

KIT $36.00

CRCEJ!

P.O. Box 6263 Bellevue, Wa. 98007 (206) 885-7038

©he mzyj&mr mratit \XAnMb*...

mt

Parasitic Intel Engineering

specification Clock Fix Kit

Note These are the actual clock wav» forms al the 8080. as produced by a Parasitic Engineering Clock Ftx Kit

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A PARASITIC ENGINEERING

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•Altair is a trademark of MITS Inc.

133

Here are 10 reasons why you should subscribe to

CREA TIVE COMPUTING today.

I

1

5

J.

Creative Computing will help you decide which computer is best for you.

Creative s no-nonsense equipment profiles arm you with the facts before you talk to the vendoror dealer Whethpr you're interested in a microcomputer kit, a mini, terminal, or programmable calculator you ll find the evaluative information you need in Creative Indeed, one wise hardware decision could save you the cost of a lifetime subscription*

Creative Computing discusses computer applications in nontechnical, understandable language.

Business people who want to know what's goiny on in the EDP department students who want to team about microprocessors, hobbyists looking to make good use of home computers, or anyone concerned about the effect of the computer on society will find these and many, many more mind-expanding topics I over_d on the pages of Cteative

Creative Computing covers computer education in depth.

After all. that's where we got our start and so we continue to present four or five major learning activities every issue If you re a teacher Cteativc will save you hours of preparation time if you re a student you'll be way ahead of your class with Creative And if you ve already graduated you can bone up on what you missed

Creative Computing carries outstanding fiction every issue.

One of the best ways of exploring future scenarios of computer usage is through fiction, so Create seeks out material from the best authors Isaac Asimov. Fredertk Pohl. Arthur C Clarke to name just a few. as well as many others who are destined to be the best of the next generation

Creative Computings book reviews are honest and timely.

We re not owned by a big book publisher to whom we owe loyalty, nor do we depend upon advertising tor our revenue Hence, not only do our reviews pull no punches, but we also rank order similar books (like all 34 books on the BASIC language which we reviewed last year) Creative reviews virtually every computer book of interest to educators, hobbyists and general laypeople even including vendor manuals and government pamphlets

An extensive resource section will save you time and money.

Every issue of Creative carries 40 or more short resource reviews evaluating periodicals booklets hardware terminals, couplers peripherals, software packages organizations, dealers and much more Every entry has a brief description, evaluation and the name address, and phone number of the vendor You'll save valuable time seeking out this information much of which you d possibly never come across

Creative Computing will provide hours of mind-expanding entertainment, even if you don't have a computer.

Creative Computing carries 10 or 12 pages of games and puzzles every issue Most of the puzzles don't need a computer or calculator to solve, some do Naturally the 4 or 5 new computer games (in Basic. Fortran, and APL) in every issue require access to a computer

Creative Computing gives you things to actually do with a computer.

Home computer kit, mini, timesharing terminal whatever your access to computer power, Creative provides thoroughly documented programs with complete listings and sample runs that you can use with minimum effort Games, simulations. CAI. computer art — whether education or recreation is your bag you'll find programs which you can use in Creative

A no-compromise policy of editorial excellence means every issue is of value to you.

We firmly intend to be around a long time and we believe the way to do that is to publish only material of the very highest quality We believe our readers are among the most astute intelligent, and active people in the world You can't afford to waste time reading imprecise, opinionated, or wordy articles and you won't find any in Creative

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That same $21 will buy you a pairof Star Trek walkie talkies, six direct dialed 10 minute calls between New York and Boston. 3 tankfults of gas. or 10 cocktails at a Hilton hotel Wouldn't you rather have 18 issues of Creative Computing each containing over 85 pages of solid editorial material (including advertismq over 100 paqes per issue) Count the editorial pages in any other hobbyist or special interest magazine and compare it to Creative Any other 1 year subscription $8 Lifetime $300

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~sl7l«C^TpTIONl)Rr5EirFOR]^

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systems software programs for the popular processors,

What About Source Code?

When publishing object code for extended programs, such as Jack's assembler, or a BASIC interpreter or other software, the length of the source listings preclude reproduction in the magazine. The source code of the Tiny Assembler runs 40 pages for example. To provide the source code for those individuals seriously interested in modification and extension of programs of this form, PAPERBYTES will be making available extended documentation for programs including users manual information, source listings, a reprint of any BYTE articles discussing the programs, and additional documentation depending upon the type of program being published. The PAPERBYTES release of Jack Emmerichs' assembler user's manual is in preparation coincident with preparation of his articles for publication."

Attention, Engineers of Bar Code Readers:

On page 320 of the November 20 1976 issue of EDN magazine, there is a short note sent in by Wesley Grenlund of Beloit Corporation, Rocton IL, concerning a signal processing circuit for scanners. The circuit combines a Texas Instruments Tl LI 39 source-receiver assembly with the 75140 line receiver to make a TTL level input to the single bit port needed by bar code scanning software. The only additional part probably needed is some slit optics (.01 inch [.0254 cm] wide for our bars) to define a limited active area. The slit would be positioned in front of the intersection point of the source beam and the receiver viewing path, as suggested by Dave LeVine.

We received a similar hint to use the Tl LI 39 in early October from Dave (who is chief engineer of Computer Link, Burlington MA). Dave says he has successfully used the TIL139 together with a single National Semiconductor 74C14 hex Schmitt Trigger integrated circuit as the sole input processing amplifier: This version uses one of the Schmitt triggers in the package as a capacitively coupled amplifier (open loop and saturating), with the remaining five triggers ganged in parallel to drive a TTL unit load from the output of the first trigger. This hint popped out of Dave in the context of the usual "micro session" (would be called "bull sessions" in any other field) which occurred at the October 1976 meeting of the New England Computer Society."

Boards DO Something

a*

«*, i § tilt i i i i t i I

CL2400

Real Time Clock

$98—Kit

$135—Assembled

If your system needs to know what time it is, our CL2400 is the board for you. The present time in hours, minutes, and seconds is always available for input, and is continuously updated by the highly accurate 60 Hz power line frequency. Need periodic interrupts? The CL2400 can do that, too, at any of 6 rates. Reference manual with BASIC and assembly language software examples included.

PC3200

Power Control System

\: 5! fe£

PC3232 $299—Kit PC3216 $189—Kit

PC3202 $39.50— Kit

$360—Assm.

$240—Assm.

$52—Assm.

If your system needs on/off control of lights, motors, appliances, etc., our PC3200 System components are for you. Control boards allow one I/O port to control 32 (PC3232) or 16 (PC3216) external Power Control Units, such as the PC3202 which controls 120 VAC loads to 400 Watts. Optically isolated, low voltage, current-limited control lines are standard in this growing product line.

P.O. Box 516

La Canada, CA 91011

(213) 790-7957

'Real World Electronics"

CONGRATULATIONS

WE DID IT! THE 6800 IS COMPLETE

SWTPC 6800 PLUG COMPATIBLE PRODUCTS COMPLETELY ASSEMBLED

M-16 A 16K single power supply STATIC RAM memory system. The M-16 is fully buffered and requires only half the power of a similar size system using low power 2102's. With the M-16, you can expand your system to 48K and still have room left over. Price $595.

P-38 An 8K EPROM board containing room for 8 2708's. Alternately, you may use it to hold up to 7 2708's plus your Motorola MIKBUG, MINIBUG II or MINIBUG 111 ROM. Using it in this mode at EOOO through FFFF you have direct access to the restart and interrupt vectors which are then switch selectable between MIKBUG and your EPROM but still under MIKBUG control. The P-38 addressing is switch selectable to any 8K location. Together the P-38 and M-16 allow various combinations of RAM plus EPROM up to 56K. Price $179.

P-381 Contains all the features of the P-38 plus interface capability to the Oliver Paper Tape Reader and our EPROM programmer which will be announced shortly. Price $229.

P-38FF Contains all the features of the P-381 plus a plug-in interface to the ICOM Frugal Floppy. Includes one 2708 with the ICOM bootstrap software. Price $299.

PS-1 Power Supply Kit. Provides plus and minus 16 volts required for up to 5 P-38 series systems. May be wired to provide a one volt increase in the plus 8 volt supply. Recommended for any system where the 8 volt supply falls below 7.7 volts under normal load. Price $24.95.

BFD-68 Basic Floppy Disc System. Complete with controller, cabinet, power supply and one mini-floppy drive. Cabinet, power supply and controller will accommodate up to 3 drives. Includes our nifty Disc File Management software. Assembled and ready to plug into your SWTPC 6800. Price $795. Additional drive and interface cabling $429.

ALL OUR PRODUCTS EXCEPT THE PS-1 ARE COMPLETELY ASSEMBLED. AVAILABLE AT MOST SWTPC DEALERS OR FROM US BY MAIL. BANKAMERICARD AND MASTERCHARGE WELCOME.

SMOKE SIGNAL BROADCASTING

P.O. Box 2017, Hollywood, CA. 90028

135

BYTE BINDERS and FILES

BYTE's Bits

Preserve those precious first 16 issues

with either a handsome but rugged library file—or a binder—in flag blue Kivar library fabric stamped in gold leaf.

L

Wii

Files: Made to hold the first 16 issues of BYTE. Price per file $4.95; three for $14; six for $24, postpaid.

Binders: Made to hold the first 16 issues of BYTE. Price per binder $6.50; three for $18.75; six for $36, postpaid.

(Add $1 each outside USA.)

Send to: BYTE, POB 5120, Philadelphia PA 19141

I enclose check or money order for $

Please send me BYTE Files Binders

Name

(please print)

Address City

State

„Z'P,

Satisfaction guaranteed or money refunded. Allow at least four weeks for delivery.

Guinness, Take Note:

The World's First Commercial Personal Computing System Product to Use 16 K Dynamic Programmable Memory Chips . . .

A recent phone call from Steve jobs (who, with Steve Wozniac, is responsible for the Apple Computer Company) reported what is claimed to be the first shipment of a personal computer systems product built with the new 16 K dynamic memory chip products. The product which used these chips was an Apple 1 - an MOS Technology 6502 proccessor board with 32 K 8 bit bytes of memory (16 chips), read only memory systems software, and video interface. The board was delivered to one of the Byte Shops in the San Francisco Bay area on December 17 1976, for sale to a retail customer.

Larger and larger amounts of memory will be the trend in small computer systems for some time, due to the combined factors of its immense desirability as a programming resource and the dropping prices of the new LSI semiconductor technology. The use of the 16 K chips in Apple was made possible by the fact that the manufacturer of these memory parts chose to make the 16 K designs essentially pin compatible with their older 4 K designs by using a change in the logical interpretation of one of the lesser used pins of the package. This pin now serves as the seventh address bit in each of the two 7 bit address segments which form the 14 bit address needed for a 16 K bit array. The Apple product demonstrates the success of this idea since it will take any combination of 4 K and 16 K chips in byte wide groups. Watch very shortly for advertisements of the new Apple II computer, both as a finished product and as a board level computer which looks like it will be an excellent and innovative addition to the marketplace."

A HAM Swapfest

The 7th Annual North Florida Swapfest sponsored by the Playground Amateur Radio Club (PARC) will be held in Fort Walton Beach FL at the Okaloosa County Shrine Fairgrounds on Saturday, March 19 and Sunday, March 20 1977. The Swapfest will be a full weekend affair with the display area open from 8:00 AM to 4:00 PM each day. A dinner, featuring a prominent speaker, will be held at the Fort Walton Beach Holiday Inn Saturday evening. The North Florida Swapfest is an annual event, sanctioned by the American Radio Relay League (ARRL), and draws hundreds of Radio Amateurs and electronics experimenters primarily from Louisiana, Mississippi, Alabama, Georgia, and Florida, although

136

amateurs from many other states attend. The North Florida Swapfest is a nonprofit function and proceeds are used to finance local Amateur Radio projects, the next year's Swapfest and the Playground Amateur Radio Club Scholarship Fund. Interested in information on booths or attendance? Contact Bill Callanan WB4FTA, Swapfest Chairman, Playground Amateur Radio Club, FOB 433, Fort Walton Beach FL 32548."

A Mention

MICROCOMP is a new computer store, dealer of OSI products, located at 785 S Main St, Fond du Lac Wl 54935. Phone (414) 922-2515, or write Nyles Priest of MICROCOMP.*

BYTEs Begs

Why the DACs "Don't Work"

Author Steve Ciarcia sent our way (via his friend Chris Morgan who stopped by one recent Saturday) the following correction to his article "Make Your Next Peripheral a Real Eye Opener" on page 78 of November 1976 BYTE. In the schematic of pages 84 and 85 (figure 2), we (Steve or CH at BYTE? Who knows?) omitted notation of the negative supply pin for the MC1408-L8 digital to analog converters, IC4 and IC5. Pin 3 of each 1408 should be wired to the —15 V supply."

Weathering the Storm

Author Mike Firth, whose or tide "Do It Yourself Weather Predictions" appeared on page 62 of December 7976 BYTE, sends in the following items:

In my article on the weather, a call from Tom Harper in Miami FL has put me on the track of two problems, which I describe below:

On page 66 (BYTE December 76), the simple formula for relative humidity (H = 100% - T*5) is said to be for centigrade temperatures, but in fact it is for Fahrenheit, an error caused by an error in my original source. To use the equation for centigrade temperatures, the 5 should be changed to an 8.

In using the more complex formula, three different values of E, the vapor pressure, must be used, but my article made it seem that only two were needed. Two are obtained from a table or by interpolation from the values given at the top of page 66. They are Ew, the vapor pressure of water at the wet bulb temperature, and Ej, the vapor pressure of water at the dry bulb temperature. The third value is E, the actual vapor pressure in the air from the formula. The proper formula for relative humidity is then:

RH - E/Ed (not RH = E/Ew as given in the article)."

SOFTWARE

8080 PACKAGE

AS PROMISED TSC IS RELEASING THE 8080 ASSEMBLER LANGUAGE GAME PROGRAM PACKAGE. THIS IMPRESSIVE COLLECTION OF SOFTWARE INCLUDES THE POPULAR GAMES ACEY-DUCEY, HANGMAN. MASTERMIND SWITCH. HURKLE AND A TSC RANDOM NUMBER GENERATOR. THE PACKAGE CONTAINS WELL COMMENTED ASSEMBLED SOURCE LISTINGS. SORTED SYMBOL TABLE. HEX DUMP, INSTRUCTIONS AND SAMPLE OUTPUT. ALL IN AN ATTRACTIVE BINDER. NO TAPES AVAILABLE AT THIS TIME. ORDER PD80-1 $19.95

6502 PACKAGE

A PACKAGE IDENTICAL TO THE ABOVE IS AVAILABLE FOR 6502 BASED SYSTEMS. THESE PROGRAMS ARE JUST WHAT YOU NEED. PD65-1 $19.95

PROGRAM OF THE MONTH CLUB

PROGRAM OF THE MONTH CLUB IS A UNIQUE SERVICE AVAILABLE TO THE HOBBYIST. FOR $2.00 YOU WILL RECEIVE A 1 YEAR MEMBERSHIP WHICH INCLUDES A MONTHLY NEWSLETTER DESCRIBING THE NEWEST 6800 6502. AND 8080 SOFTWARE RELEASES FROM TSC. UP TO A 157. DISCOUNT IS OFFERED TO MEMBERS ON FEATURED SELECTIONS. POM $2.00

ORDERING INFORMATION

PLEASE INCLUDE 3*/. POSTAGE. INDIANA RESIDENTS ADD 4V. TAX CUS FUNDS ONLY). CHECK YOUR LOCAL DEALER FOR OUR PRODUCTS. (DEALER INQUIRIES WELCOMED). SEND $.25 FOR fl COMPLETE CATALOG.

TSC

TECHNICAL SYSTEMS CONSULTANTS

BOX 2S74> U. LAFAYETTE INDIANA 47906

TSC

Computer System Engineers

Computer Transceiver Systems, Inc., manufacturer of portable computer terminals, is expanding its R&D facilities. New developmental programs getting under way are specifically directed towards state-of-the-art applications of microprocessors and allied LSI components into the CTSI product line. Positions are open in several areas for knowledgeable, enthusiastic individuals who would like to join a small dynamic company and tackle challenging and rewarding projects.

MICROPROCESSOR SYSTEM ENGINEER

Qualified individual shall have a minimum of 10 years of design experience including 1-2 years of system design and implementation using microprocessors. Knowledge of TTL, MSI, and LSI essential. Ability to develop electro-mechanical interfaces desirable.

Designer shall also be capable of developing test equipment for use by manufacturing and field service.

SENIOR ELECTRONIC ENGINEER

Innovative engineer with a minimum of 5 years of experience with high-speed logic systems, and with hands-on experience with microprocessors. Must be familiar with TTL, MSI. and LSI components. Experience with power supply and analog circuit design desirable but not essential.

SENIOR LAB TECHNICIAN

Qualified applicant shall have a minimum of 5 years of experience assembling and testing prototype electronic systems. Must be familiar with the use of laboratory test equipment and must be capable of layout and breadboard assembly from schematics. Should be familiar with digital logic.

Send resumes to the attention of Mrs. Diane Palmer, Computer Transceiver Systems, Inc.. P.O. Box 15, Paramus, N.J. 07652.

137

How To Make Your Computer Even More Boring..

Interface it with a Midwest Scientific Instruments FD-8 Floppy Disk Memory System.. .with all your disk software on our PROM/RAM Board.

With our FD-8 system and FDOS firmware, your computer is always ready to gov With the disk operating routines on PROMS, all you have to do is load your desired program from disk and start running. Of course you may MM^have.to wait 5 or10 seconds for your program to

■^^ toad If you have lots of memory.

The FD-8 interfaces to any microcomputer system via a single PIA chip,.. and all of our available software is included at no additional charge.

MSI FDOS operating system software has many outstanding features...

• Automatic program loading and linkage

• Auto error recovery

• Dynamic space allocation and file extension

• Utilities for file listing, copying, deleting, or renaming

The FD-8 is complete, including cabinet, all power supplies, and cables.

Prices:

FD-8 Floppy Disk System

Kit $1,150.00

FD-8 System Wired

and Tested $1,395.00

PROM/RAM Kit (SwTPC

6800 or 8080) $95.00

PROM/RAM Wired & Tested,

with FDOS Firmware (specify

6800 or 8800 System) $345.00

PR-1 Programmer & Verification Module

Designed to program 1702A PROMS, the MSI PR-1 interfaces with any microcomputer system via a single PiA chip.

A complete software package is furnished with the system at no additional charge. This gives you the ability to transfer any area of memory to a PROM chip.. .read the contents of a PROM into memory., .calculate checksums for ROMS.. .and duplicate ROMS. Following PROM programming, the software reads the PROM back into memory and compares each step with the memory content from which it was programmed for verification.

The PR-1 is complete, including cabinet and power supplies. PR-1 $325.00

Send for New Free Catalog

Here are two MSI Dealers who can show you our products in action Microcomputer Systems, Inc., 144 S. Date Mabry Ave., Tampa, Florida 33609 813/879-4301

American Microprocessors, Equipment & Supply Corp., Chicagoland Airport, P.O. Box 515, Prairie View, Illinois 60069 312/634-0076

220 West Cedar

Olathe, Kansas 66061

913/764-3273

TWX 910 749 6403 (MSI OLAT)

•Before I forget.. .send me information •

• about the FD-8 Memory System.. .and •

• your new catalog. •

• • #Name #

• Address *

• •

• City •

State

.ZiP.

BY177 •

MSI is a dealer for Southwest Technical Products • Mastercharge & Bank Americard Orders Accepted

HOUSTON now has a full service outlet for microcomputers and accessories. Microtex, Inc., located in the Southwest section of Houston, Texas carries product lines from the following manufacturers.

. IMSAI -LEAR SIEGLER

• SWTPCO • NATIONAL MULTIPLEX

. TDL • ICOM

For your professional application or your own personal system, we can help furnish all your computer needs.

Microtex, Inc.

9305 - D Harwin Dr.

Houston, Texas 77036

713-780-7477

Pictured above is the new OP-80A High Speed Paper Tape Reader from OAE. This unit has no moving parts, will read punched tape as fast as you can pull it through (0-5,000 c.p.s.), and costs only $74.50 KIT. $95.00 ASSEMBLED & TESTED. It in eludes a precision optical sensor array, high speed data buffers, and all required handshake logic to interface with any uP parallel I/O port.

To order, send check or money order (include $2.50 shipping/handling) to Oliver Audio Engineering, 7330 Laurel Canyon Blvd.. No. Hollywood. CA 91605, or call our 24 hr. M/C-B/A order line: (213) 874-6463.

8,192 X 8 BIT STATIC MEMORY

EXCEPTIONALLY LOW POWER

HBjfe i & i i & i,

urn

KIT $295.00

PROTOTYPING BOARD

2-80 - CPU

16K RAM

EXTENDER CARD

2K RAM/2K ROM

CARD RACK AND POWER SUPPLY

LOW PROFI LE IC SOCKETS

EDGE CONNECTORS

DB25 CONNECTORS

SHIPPING EXTRA, ADD $2.00 NJ RES. ADD 5% SALES TAX

ELECTRONIC CONTROL TECHNOLOGY

P.O. Box 6, Union, New Jersey 07083

Microcomputer

Equipment

Survey

Can Help You Find

The Best Equipment

And Save Money

Prices and full specifications for more than 100 products from 30 manufacturers. Describes Systems, CPUs, RAMs, PROMs, Tape and Floppy Disk Drives, Keyboards, Video Displays, D/As, A/Ds and more.

Volume 1 $5.00 postpaid

Computer Systems Design

1611 E. Central Wichita, Ks. 67214

JB/DDEl7ELQ«DE(\ITL4B5

P. O. Box 2345

W. Lafayette, IN 47906

(317) 463-7167

U watt carbon film resistors $0.03

5 percent, 50 per value min.

^ watt carbon comp resistors ..$0.02

10 percent, 50 per value min.

No-Nik wire strippers $16.00

10,12,14,16,18,21,23,25,28,31 34,37,44 or 54 thousanths wire diameter

Carbide PC board drills

wire size: 55 65 $2.88

66 70 $2.97

71 75 $3.06

76 78 $3.60

79 ■ 80 $3.60

Spec sheets are available.

We would be pleased to send you a 'GOODIES' catalog listing all kinds of hard to find products including: AAolex Bishop Graphics, AMP, CDC manuals and forms, PC drills and mills, electronics tools, PC board manufacturing supplies, resistors, and semicon ductors.

pCOMPUTER

PROGRAMMING

COURSE

Free description and outline of Modu-Learn TM Home Study Course in microcomputer programming. Hundreds of pages of text with examples, problems, and solutions. Prepared by professional design engineers using the best software design techniques from structured programming and practical experience with microcomputers. Presented in a modular sequence of 10 lessons oriented for the new programmer. Extensive reference material you will use long after you become an accomplished microcomputer software designer. Much of the information in the course has been available only through costly seminars. Now you can purchase this complete home study course for under $50.00. Send for free descriptive brochure now.

SERVICES INCORPORATED

711 Stierlin Rd, Mountain View, CA 94043 (415) 965 8365

CSIassified Ads

FOR SALE: ASR-33 TTY with adjustment and parts manuals. Very good condition, $700. With acoustic coupler, $750. Donald Bailey, 19 Shaker Rd, Concord NH 03301, (603) 224-0486.

FOR SALE: Two MITS 88-MCD 4K dynamic memory cards for Altair 8800, assembled, completely tested, meet specs for use with disk, $200 each, including edge connector. Vintage BYTEs, issues 1 through 4, $5 each. David Richards, 6655 Hill St, El Cerrito CA 94530, (415)529-0759, evenings.

FOR SALE: Attention computer hams: Morse to ASCII decoder. All controls accessible from front panel. Work with TVT 1 or TVT 2. I have helpful documentation on the decoder that I will pass along on request for $1.50 to handle cost of photo copies and postage. Asking $75 for the unit. Write Jack S Davis, POB 5, Endwell NY 13760, (607) 754-0309.

FOR SALE: E and L Instruments MMD-1 8080A based microcomputer complete with keyboard, 256 bytes RAM, 256 bytes of PROM programmed for keyboard entry and execution of programs, power supply, interfacing and breadboarding socket, case, and 40 pin edge connector for expansion. Includes modular, self-taught, microprocessor course. Assembled, tested, excellent condition, $300. Richard Criscuolo, 303 Oak Av, Lindenhurst NY 11757, (516) 884-3882.

SWAP OR SELL: SWTP CT-1024 TVT 2 with serial IO, manual cursor, screen read, P/S. Two Altair 8080 CPU boards, Tarbell interface, HAL ST-6 Teletype converter with all options (can be used as a modem). All in like new condition and guaranteed perfect. Need hard copy printer or ??? Michael Shrayer, 930 S Bonnie Brae St, #331, Los Angeles CA 90006, (213) 380-6509

FOR SALE OR SWAP: Texas Instruments SR-52 card programmable calculator, complete with all standard accessories and manuals. It has a special programming manual with many programming tricks, procedures for accessing 60 data memories, and procedures for reading and writing data onto cards, $200 or fair trade for S100 bus, AltairIMSAI, compatible memory or IO. R W Toy, 155-A Duncan, San Francisco CA 94110, (415) 648-6105.

WANTED: November 1975 issue of BYTE. Will consider purchase or trade for this issue only, or possibly, for a set of issues. Chris Bauer, I EMS Dept, Florida Technological University, POB 25000, Orlando FL 32816, (305) 275-2236.

FOR SALE: Friden Flexowriter Baudot Teletype with five level paper tape punch/reader plus card reader. Can be converted to ASCII, $95. Derek Hendry, 64 The Uplands, Berkeley CA 94705, (41 5) 654-5583.

Readers who have equipment, software or other items to buy, sell or swap should send in a clearly typed notice to that effect. To be considered for publication, an advertisement should be clearly noncommercial, typed double spaced on plain white paper, and include complete name and address in forma tion. Th ese n o tices a re free o f charge and will be printed one time only on a space available basis. Insertions should be limited to 100 words or less. Notices can be accepted from individuals or bona fide computer users clubs only. We can engage in no correspondence on these and your confirmation of placement is appearance in an issue of B YTE.

Please note that it may take three or four months for an ad to appear in the magazine.*

WANTED: Software and hardware schematics for music synthesizers (computer controlled or not). I am especially interested in automated music composition. Bill Struve, 505 Meade Cir, Memphis TN 38122.

WANTED: SCCS Interface issues December 75, February 76 and March 76. Please let me know if you have them for sale. Thomas R Saley, 279 Gehring Rd, Tolland CT 06084, (203) 872-7084.

FOR SALE: Mostek F-8 evaluator kit fully assembled and working with literature. Two complete Viatron 2100 systems working with the complete literature pack. The first check (certified) or M O for $900 takes all. Donald E Scherck, Rt One, Collbran CO 81624.

SITUATION WANTED: Research physicist, with several years practical digital design experience, breadboarding, prototyping, etc; thorough reading knowledge of microprocessors and software. Looking for position with computer store, computer consultants or similar, in which my abilities can be traded for salary and chance to learn micros. Jay Kirsehenbaum, 350 E 30th St, Apt 4L, New York NY 10016, (212) 684-5525.

NEED: BYTE issues 1, 2, 3, 8, 9 and 10. Willing to swap money for them, but have surplus copies of other issues of BYTE as well as assorted test equipment and digital hardware and components. How about a handful of 2102s? Hank Irvin, Dept of Physics, Tulane University, New Orleans LA 70118.

WANTED: I will buy your new, used, or dead Altair 8800, working or not, for cash, t am desperate for Altair. Help out a poor college kid. I will also trade for your machine. I have a scope and a Teletype. Call anytime. Jim Webb, POB 5224, Carson CA 90749, (213) 325-4684.

FOR SALE OR TRADE: PDP-8 mini-computer (straight-8), mounted in attractive walnut cabinet (spouse-approved for den). Complete with maintenance manual, drawings, 4 K BASIC, 4 K FOCAL, editor, PAL III assembler, disassembler, TTY interface, games, etc. Perfect condition. Free DECUS membership available for additional software. Presently in use with ASR model 33 Teletype. Can be sold with or without model 33. Sale price W/O Teletype $800. Rex Engle or Jim Speidel, POB 10498, Charlotte NC 28288, (704) 374-6409.

TERMINALS: BURROUGHS 9350-2, ASCII, 15cps upper and lower case, $200. Friden Flexowriter, model SPS with paper tape reader and punch, $200. Univac DCT500, 30 cps printer, no power supply or interface, $100. Phil Hughes, POB 2847, OlympiaWA 98507.

FOR SALE: Altair 8800 system with 8K RAM, 88-SIOA, 88-ACR, 8K BASIC, assembled and running, $1167. SWTP CT-1024 complete, unassembled, less monitor and case, $275. Friden ASCII communications terminal from Herbach and Rademan with control unit, $200. Chris Foreman, POB 127, Reseda CA 91335, (213) 342-8845.

WANTED: BYTE issues for October and November 1975; April, May and June 1976. Please notify the following indicating price desired: Technical Library, Bell Telephone Laboratories, Western Electric Co, 2525 Shadeland Av, Indianapolis, IN 46206.

FOR SALE: Cryptographic program that will baffle the codebreakers of the CIA. Encode and/or decode your private correspondence for maximum security. Documentation of cypher technique, program listing and punch paper tape in BASIC for only $6. Jon Stedman, 1528 Summit Rd, Berkeley CA 94708.

FOR SALE: Pacer: a 16 bit micro with TTY interface, line assembler in ROM and complete documentation. Assembled and running in cabinet with 32 key control assembly. Call (213) 243-5179 or write POB 430, Glendale CA 91206.

WANTED: Back issues of BYTE. Desire 1 copy each of issues 1 through 14. Will pay $3 for each complete issue in good condition. Call (313) 323-3574 or write R Parenteau, 11020 Burlington #409, Southgate Ml 48195.

WANTED: Back issues of BYTE magazine: issues 2, 3, and 8. Please send price and condition information to Art Leyenberger, 142 Kenilworth Rd, Ridgewood NJ 07450.

WANTED: BYTE magazine issues 7, 8, 9 and 10 in good condition only. Frank E Marfai, 2839 Hermosa Av, La Crescenta CA 91214.

FOR SALE: Brand New ASR-33 Teletype with auto reader. I reconfigured in midstream and will sell this superb $1,188 value for only $950. Immediate delivery instead of usual 4 to 6 month wait. J Katz, 1921 Pelham Av, Los Angeles CA 90025, (213) 474-3347.

FOR SALE: Altair 8800 computer, well built and checked out, $500. Two MITS 4 K RAM boards, $150 each. One PTech 4K RAM board, kit untouched, $120. One 4 K X 8 EPROM board with assembled monitor, $150. One MITS RS/232 S10 board, $100. SWTPC TVT 2 with 510 and PS and keyboard and monitor, $300. SWTPC cassette interface well built unchecked, $70. 32RO TTY new, $300. Best offer takes any or all. Louis Doctor, BARH D311, RPI, Troy NY 12181, (518) 270-7586.

CHANGING HOBBIES: Want to swap miscellaneous ham gear for computer and/or peripherals. Have Heath SB-303 with optional crystal filter and other items too varied to list. Also have near new Heath stereo mike mixer and miscellaneous test equipment, all in good condition. Also willing to swap professional (First Class Federal License) assembly service or technical assistance for devices. Call or write Mike Hales, Route 1, POB 30W , San Juan TX 78589, (512) 383-7233.

WANTED: Manual or schematics and timing information for IO circuits of IBM model 72 Selectric typewriter/terminal. C G Bothner, POB 153, Landing NJ 07850.

FOR SALE: Tektronix model 611 graphics storage display scope, $450. Also have Tektronix model 581 oscilloscope with type 82 plug in and scope mobile, $400. Will trade for Altair 8080. Don Heinlein, 1546 E 215th PI, Carson CA 90745, (213)830-4225.

FOR SALE: Altair 8800a, 16 slot memory board, fan; two 4K dyn, two 4K static, (16 K total memory); ACR IO; 3P+S IO; TVT 11 with 64 characters per line; SCM Telewriter; software. $2150. Will separate. Evenings: (312)328-5610.

FOR SALE: GE core memory 16 K by 40 bits, all power and interface circuitry and documentation — been used with an 8080 processor. Litton Industries drum memory with full read write electronics. Bryant MBM drum memory. By unit or best offer over $250 for lot. C H Eby, 7101 Mammoth Av, Van Nuys CA 91405, (213)988-1763.

FOR SALE: Microprocessor system by Control Logic. Contains three basic cards; central processing unit using an 8008 input output control providing clocking and processor control signals, and memory address storage which provides latching registers for memory and output data control and a 256 byte PROM. Also included: 1 K of 2102 RAM, card mounting hardware, and logic diagrams, $100. K Talen, 10605 Double Spur Loop, Austin TX 78759, (512) 258-4282.

FOR SALE: PolyMorphic VTI 64 video module, 64 characters per line, keyboard input port, Greek control characters, $200. Morrow's Godbout Cassette Interface (BYTE Standard) fully expanded, with 3 cassette channels, parallel and RS-232 TTY IO ports, and operating system in EROM, $120. Both boards assembled and working with ICs in sockets, and postpaid in continental US. Shipped within 24 hours of receiving MO or certified check. Tom Burke, 150 Church St, Burlington VT 05401.

MICRODATA REALITY: Are there any other computer hobbyists using this system? If so, I'd like to say hello, swap notes and programs, etc. Would also like to know where to buy a 4 or 8 way video terminal interface card and other peripherals for Microdata Reality (Model 1600 processor). Jack Hardman, 140 Forest Av, Glen Ridge NJ 07028, (201) 429-8880.

140

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_

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TEC 9900-SSUF, 16 bit T19900 microP. 32 bit 1/0. hardware mutt & div, buffered bus, 20 ma or RS 232. 8 s & sockets $259.00

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8080 PPI $10,00

8212 I/O port $2.50 8224

8228 (

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Nat. Multiplex Digital Tape recorders ft kits 10% OFF LIST

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Slobs and Newsletters

Conducted by Peter Travisano

HP-65 Users Club

The HP-65 Users Club is by, of and for those people around the world who use and enjoy Hewlett-Packard calculators. Its newsletter 65 Notes is a must for anyone stuck on these machines. Volume 3, Number 9, is a special games and programs issue. HP-25 Roulette is a mathematical duplicate of the Monte Carlo original, complete with broken bank. Depending on your imagination or your friends' bank accounts this program could conceivably save airfare to Las Vegas. Another program for your HP-25 is Battleship II, a game which starts with random shooting at your opponent's hidden fleet until a discernible pattern appears; after that, it's a race to sink the enemy's ships as quickly as possible. Number Guesser is a handy way to decide all kinds of distasteful things like whose car do we take or who pays for iunch: sort of an electronic short straw.

There are plenty of other games and ideas. So if you want to get the most out of your Hewlett-Packard calculator, be sure to send for more information from the HP-65 Users Club in care of Richard J Nelson, 2541 W Camden PI, Santa Ana CA 92704.

Dayton Microcomputer Association Formed

Looks like Dayton OH hackers are off to a fine start with well over 100 hobbyists working together to form a new club.

Meetings take place on a regular basis, 7:30 PM on the last Tuesday of each month. For more information write Dayton Microcomputer Association, in care of Dayton Museum of Natural History, 2629 Ridge Av, Dayton OH 45414.

Montreal Micro 68 — Club des Mordus d'el Ordinateur — Computer Club

The world's first bilingual computer club has been organized in Montreal. Among other projects, Micro 68 plans to exchange computers, hardware applications and software with other clubs in the US. For more information, get in touch with John

Courtney, president, Montreal Micro 68 Computer Club, Case Postale al Succur Sale, Montreal CANADA H4Y 1A2.

Denver Amateur Computer Society — INTERRUPT

There are newsletters and there are newsletters, but DACS* fine publication, INTERRUPT, ranks with the superb handful that begin to invade the area of the print media set aside for magazines. There are plenty of interesting and competent features on micros.

Dealing with DACS is a good way to learn more about computers; they'll even help you get a club started in your area, which is probably the best way to share and spread knowledge.

Interested? Get in touch with the Denver Amateur Computer Society, POB 6338, Denver CO 80206.

Analytical Engine — Chesapeake Microcomputer Club Inc

Another newsletter that has helped set the standard in the micro hobbyist field is the Analytical Engine, the publication of the Chesapeake Microcomputer Club Inc, 236 St David Ct X-4, Cockeysville MD 21030, (301) 667-9690.

Those still looking for a basic Star Trek program might want to get hold of Volume 1, Number 6. They will also find an elementary article on kit building and another on assembling a five chip interface for those a little further along. The same issue contains a "Bibliography of Microprocessor Sources," as a handy reference of books, software, periodicals and articles. They also list similar bibliographies if this compendium isn't enough.

ON LINE — Hardware and Software

Exchange

The ON LINE people continue to publish a listing of classifieds geared to the computer hobbyist: everything a hacker could want for sale or swap, you name it. There's also a listing of clubs, with meeting schedules. If you want to place an ad or if you're just looking for a bargain, send a note to ON LINE, D H Beetle, publisher, 24695 Santa Cruz Hwy, Los Gatos CA 95030.

Southern New England — Westchester — Fairfield

We often mention NECS, the New England Computer Society, in these pages; but New England is a fairly large area with more than its share of computer buffs, especially in its southern parts. If you're a

142

SHORT COURSE

MICROCOMPUTERS:

PRINCIPLES AND APPLICATIONS

EL PASO—JUAREZ

THE UNIVERSITY OF TEXAS at EL PASO

MAY 23 - 27, 1977

Four day course plus Monday evening introductory sessions. Course stresses both hardware and software considerations of the design and application of microprocessors to real world problems. The course begins at an i nt roductory level and includes programming considerations, I/O programming and design, memory module architecture, system evaluation, cost analysis, and a general discussion of applications. The lecture topics will be illustrated using laboratory workshops.

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For additional information

call or write

Dr. Glenn A. Gibson

Electrical Engineering Department

The University of Texas at El Paso

El Paso, Texas 79968

(915) - 747-5472

the microcomputer

an introduction to reality

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OFF LEASE EQUIPMENT

Teletype ASR 33

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Modems and Couplers also available.

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We Carry:

•IMSAI, COMPUCOLOR, VECTOR, SOUTHWEST, C.S.C., CROMEMCO VECTOR GRAPHIC, SEALS •Books, Magazines, Newspapers •Sockets, IC's, Printers •Digital Cassette Equipment •Debugging Equipment

We offer Classes, Friendly Advice and Service

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* fully assembled and tested.

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Send $105 (shipping, handling and Illinois sales tax included) to

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Box 5502 Chicago, IL 60680 Phone:312-528-9045

I

Clubs and Newsletters information should be sent to BYTE, 70 Main St, Peterborough NH 03458, attention Peter Travisano.

Connecticut or Westchester hacker, you might want to drop a line to one of these addresses: Southern New England Computer Society, 257 Willow St, New Haven CT 06511; Connecticut Microists, 8612 Wendy Ln, Westport CT 06800; or WestchesterFairfield Amateur Computer Society, RR 1, POB 198, Pound Ridge NY 10576.

Japan

Thanks to the Homebrew Computer Club in Mountain View CA, we have a rather exotic address: that of the Japan Microcomputer Club. Those visiting that part of the world may want to stop in at the First Ohkura Building, 4f 2-1 Nihoubashi, Chuoku Tokyo JAPAN.

CACHE Register, Chicago

The Chicago Area Computer Hobbyists Exchange continues to publish CACHE Register, a newsletter that seems to lean toward abstract information on hardware and software; that is, there is very little editorializing, just the facts.

The people at CACHE are always glad to lend a hand to the hobbyist who needs information of any kind. Write to CACHE, POB 36, Vernon Hills IL 60061.

Minnesota Computer Society

We've had some correspondence from a new group (new at least to BYTE), the Minnesota Computer Society. Those in the Twin Cities area who would like to get together with other hackers should drop a line to MCS, POB 35317, Minneapolis MN 55435.

The Association of Time-Sharing Users

Here's a unique and really useful group for those involved in timesharing. AT/SU is dedicated to organizing and providing information and a forum for the users and industry representatives of remote computing. They publish a newsletter, Interactive Computing Press Review, a compilation of pertinent articles from various sources; Interactive Computing Directory, a two volume directory of remote computing users and suppliers updated with each newsletter; and Special Reports, a consumer's guide to timesharing services. Write the Association of Time-Sharing Users [nc, 75 Manhattan Dr, Boulder CO 80303.

Philadelphia Area Computer Society

PACS is publishing a newsletter called THE DA TA BUS. Among the features is a reprint of Dr Lance Leventhal's fine series of tutorial articles on microprocessers, begin

ning in November. Bill Goble is writing a three piece article entitled "Small Computer Bus Structure," which promises to be a fairly comprehensive series on bus signals and receiving and transmitting the bus. For information concerning the Philadelphia Area Computer Society and THE DATA BUS, get in touch with Bill McGill, University of Pennsylvania, Moore School Computing Facility D-2, Philadelphia PA 19174.

Mobile, Alabama — Anyone Interested in .. .

. . . SOL-10 Terminal Computers? R Downs is and he's looking for other folks who are, too. Contact Mr Downs at 205 Shelton Beach Rd, #53, Saraland AL 36571.

New York Amateur Computer Club

Hackers in and around "Fun City" might want to look into the advantages of joining the New York Amateur Computer Club in care of R Schwartz, 1E 375 Riverside Dr, New York NY 10025.

Ottawa

The Ottawa Computer Group has grown to substantial proportions in a rather short time. To get in on their doings, stop in at the National Research Council, 100 Sussex Dr, Ottawa, on the first Monday of the month or write POB 13218, Kanata Ontario, CANADA K2K 1X4, (613) 233-9412.

St Louis Area Computer Club

The St Louis Area Computer Club met recently for the first time, attracting hackers from both sides of the Mississippi. Apparently we have a real mix here of ages, vocations and obscure computers. To find out more, contact Lou Elkins, POB 1143, St Louis MO 63188, (314) 427-6116.

Panhandle Computer Society

We've just received word that a new computer club has formed, The Panhandle Computer Society of Amarillo TX. They meet every Friday and boast a membership of more than 30. All inquiries should be addressed to Tex Everett, 2923 S Spring, Amarillo TX 79103, or call (806) 373-8307.

A Note from Sol Libes re a National Personal Computing Society

I have just finished reading "Some Notes on Clubs" in the August 1976 issue, page 4, and must take exception to the statements you attributed to me. I fear there must have been a misunderstanding in our discussions. I certainly did not say, in regard to a national organization: "Who needs it?", etc.

144

I frankly feel there is a need for a national organization similar to ARRL. There are many reasons for it. Primary among them is the need to develop standards, both for hardware and software. We are currently faced with the problems of many manufacturers going their own way in equipment and program design and hence a great deal of noncompatibility. This causes unnecessary expenses for the amateur user. For example, we currently have more than a dozen different cassette 10 systems which are not compatible. This greatly inhibits the exchange of software in cassette form. Adherence to one recording standard would eliminate this problem.

A single club, or regional organization, is not in a position to develop standards and influence their adoption. This can only be done by a national organization.

Sol Libes, President Amateur Computer Group of NJ

UCT1

1776 Raritan Rd

Scotch Plains NJ 07076

Sorry about the misunderstanding, Soi. I came away with the impressions printed in that issue . . . CH.»

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Replaces and upgrades ALTAIR/ I IMSAI front panel and CPU boards, or forms the nucleus of a custom system.

This isn't a toy...or a conversation piece...but a tool for serious program development, rivalling the sophistication of many minicomputer systems. Granted no system can make bugs go away \ but this one, finally, makes them manageable.

Two exclusive operating modes give you control over real time, allowing you to work on a program while it's running.

The "Control Halt" mode refuses to let the 8080A CPU go dormant upon executing a HALT instruction; instead, special purpose hardware forces a NO OP instruction then passes control to the front panel program, where you can examine and alter processor registers .. .memory locations...and I/O ports directly from the

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The "Slow Step" mode allows you to run through a program at a variable rate from 1 to 65,000 steps per minute. The display indicates the program counter and a processor register of your choice.

Unambiguous readouts replace blinking LEDs; a 12 pad keyboard replaces time-consuming toggle switches. And because the front panel/CPU is Altair buss compatible, you can build a custom system around this board using Altair compatible peripherals. Also compatible with any software written for an Altair type buss.

We've made some strong claims

in this ad and given the

way some companies advertise, you have a right to be skeptical. In order to dispel any doubts, we've put together a complete documentation packet (schematic, layout, software, assembly instructions), available for $5.00 postpaid. You may be surprised to find out we've understated our case.

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BYTE's Bits

jim Warren's Official Rumors About the West Coast Computer Faire . . .

In phone conversation January 5 of this year, Jim Warren mentioned some of the plans for the banquets which will be held during the First West Coast Computer Faire. On Friday and Saturday night of the event, there will be speakers. Each night's offering will represent one speaker about the future world, and one speaker commenting about the real world of today. On Friday April 15, the real world speaker will be John Whitney, the computer animation and graphics artist who provided a fascinating show at the Personal Computing 76 show in Atlantic City last fall. The future world speaker on Friday night will be Frederik Pohl, one of the better known contemporary science fiction writers. On Saturday April 16, the real world speaker is Dr Henry Tropp, who will speak about his recently completed research project on the history of computing, commissioned by the Smithsonian Institution. The future world speaker for Saturday's banquet had not been finalized as of the time this note was written."

Want a Used Computer?

Believe it or not, there exists the friendly local used computer broker and there are enough of these fellows around apparently (13 in 13 different cities) to warrant a somewhat classy service organization run by Arthur F Phinney and called the Computer Multiple Listing Service, located at 3212 Chichester Ln, Fairfax VA 22030. This organization puts out a 16 page pamphlet which describes some of the mechanics of computer brokerage and the ways in which computer purchases can be arranged. We wouldn't expect much traffic in $2000 personal systems here, but if you want to look into a bargain price for a model X big computer this might be the place to start."

Notes on "What Is It?"

In December 1976 BYTE we ran a little query on page 96 concerning a cross section of an unidentified product. The answer appeared in the January 1977 issue of BYTE on page 104. The question elicited several responses, but only one correct response. Floyd Largent, of the Abex Corporation, Engineered Products Division, Mill St, Athens OH 45701 writes: "The product in your "What Is It" photograph is a porous plastic used to hold ink for computer printout devices."

But some of the wrong answers were just as interesting as the picture itself.

Attention Manufacturers

Personal computing equipment manufacturers and suppliers are invited to participate in the 1977 National Computer Conference personal computing exposition to be held in Dallas TX, June 13-16. The NCC, sponsored by the American Federation of Information Processing Societies Inc (AFIPS) and four of its member societies, will be the year's largest gathering of data processing users ,anc! computer professionals.

Full information on the Personal Computing Exposition, including brochure, floor plan, and application forms, is available from the AFIPS Exhibit Sales Office, 210 Summit Av, Montvaie NJ 07645, (201) 391-9810.

The 77 NCC, recognizing the size and importance of the personal computing market, will feature a commerical exhibition by equipment manufacturers and suppliers of personal computing products and services. The Personal Computing Exposition will be in the North Hall of the Dallas Convention Center one level below the main NCC exhibit hall. Reservations for linear booths (minimum size 10 feet by 10 feet at a cost of $600) are currently being accepted. As a special service to participating exhibitors, packaged booth displays are being made available as part of the overall cost.

In addition to the Personal Computing Exposition, the NCC will also feature a Personal Computing Fair where individuals and groups will display noncommercial systems and equipment. Personal computing will also be covered in a variety of NCC events including a two day program of sessions, and a computer club congress."

Two people identified the item as a scanning electron microscope picture of a printed circuit board. One person identified it as an electron microscope picture of "the actual atomic lattice of a conducting material, copper wire or something ..." (Only problem: Resolution for typical electron energies is just not that good.) One person opined that it was "an experimental optical read only memory consisting of microencapsulated spheres of a black fluid sandwiched between two transparent planes. A relatively high power beam of light is used to write bits by exploding a sphere containing the fluid, while a low power beam reads the blots created as bits." Another identified it as a cross section of a bubble memory. The most common answer, which actually is not far from the mark, was that the picture was a cross section of the commonly used conductive foam in which integrated circuits come packaged. In appearance, it is probable that a closeup photo of such foam might indeed look very similar to the photomicrograph of the inking matrix.

We extended Floyd's BYTE subscription by one year as an informal prize on this informal contest."

Programmers Invited to Participate in 1977 National Computer Conference Programming Contest

This announcement arrived two days after the February BYTE was on the press, but if you hurry, you'll be able to meet the March 1 deadline ... by writing your own "official entry form" as well as the contest entry.

Programmers who attend the 1977 National Computer Conference, June 13-16, in Dallas TX will have an opportunity to participate in the 1977 NCC National Programming Contest. All contestants will be competing for prizes, trophies, and plaques, as well as the chance to gain the title of "1977 National Champion Programmer."

According to Dr Portia Isaacson of the University of Texas at Dallas, 1977 NCC chairperson, "The 77 NCC special activities committee has organized this 'first' National Programming Contest in an effort to involve computer professionals more directly in conference activities. Approximately 240 applicants will be selected to participate in a test of logic and programming skills."

Directing plans for the contest is Dr C E Rodriguez of East Texas State University. Dr Rodriguez reports that there will be no requirement for a particular programming language. Entrants selected will receive a list of specific languages, terminals, and timesharing services to be used in the contest. Contestants will be selected based on the quality of their solutions to a sample problem which will be made available on request.

Deadline for all entries is a postmark no later than March 3 1977. Official entry forms and sample problems may be obtained by writing Dr C E Rodriguez, Computer Science Dept, East Texas State University, Commerce TX 75428."

A New Virginia Polytechnic Institute Seminar Program

David G Larsen forwards these two notices of a new series of microprocessor related seminars to be held at VPl in June of this year:

Microcomputer Interfacing Workshop, June 9, I0, 11, 1977. A three day workshop based on the popular microprocessor. Over 20 operating 8080 computers are available for participant use. Digital Electronics for Automation Workshop, June 7, 8, 1977. A two day workshop based on the small scale and medium scale TTL integrated circuits. Many hours of laboratory time with individual breadboarding stations will be provided along with indepth lectures.

For more information on these workshops contact Dr Norris Bell, VPl and SU Continuing Education Center, Blacksburg VA 24061, (703) 951-6328."

146

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THESC/MP at $95.00

SC/MP, the Microprocessor kit from National Semiconductor includes everything you need to build a completely functional microprocessor system - featuring the National SC/MP microprocessor — the low cost microprocessor for every application: Text Systems and Instrument Control; Machine Tool Control; Small Business Machines; Word Processing Systems; Educational Systems; Multiprocessor Systems; Proces Controllers; Terminal Control; Laboratory Instrumentation; Sophisticated Games; Automotive Controller and Appliance Controllers.

The kit, neatly packaged with all the components and literature you need, in a looseleaf binder, includes: The SC/MP Microprocessor — a single-chip Central Processing Unit in a 40pin, dual in-line package. Features static operations, forty-six instruction types; single-byte and double-byte, software controlled interrupt structure, built in serial input/output ports; bidirectional 8-bit TRI STATER bus, parrallel data/port and latched 12-bit TRI-STATER address port. ROM - 512 bytes (8-bits/byte) of pre-programmed ReadOnly-Memory containing KITBUG—a monitor and debugging program to assist in the development of your application programs, KITBUG provedes teletypewrite input/output routines and allows examination, modification, and controlled execution of your programs. RAM 256 bytes of static read/write memory for storage of your application programs. Transfers of data to and from RAM are controlled by SC/MP and KITBUG. Teletypewriter Interfact including buffer and drive capability for a 20 MA current loop interface. Voltage Regulator. Data Buffer—providing interface between memory and bidirectional data lines. All the literature you need, including schematics and programming manuals. Timing Crystal-providing 1.000 MHz timing signal. Plus all the passive components and circuit board with 72 pin edge connector required to build and interconnect your microprocessor system with external hardware.

SC/MP KEYBOARD

ASCII KEYBOARD

(Reg. §58.85)

$53.00

This 63 key ASC II Encoded Keyboard kit was designed and manufactured by Electronics Warehouse Inc. Features: single 5 volt D.C. supply, utilizing only TTL logic elements {no MOS devices to blow), TTL drive capability (each of the eight bits of ASC II output will drive the equivalent of ten standard TTL inputs without external buffer drivers), de-bouncing, upper and lower case fully ASC II, 8 bit parallel output. In addition to the alpha-numeric and symbol keys available on a regular keyboard, the following keys are utilized; escape, back-space, tab, line-feed, delete, control, shift-lock, shift'{2 keys), here-is, control-release.

Kit includes: 63 key keyboard, P.C. board, all required components and assembly manual with ASC II code list. Optional: 1. Parity bit-add $1.00 Aluminum enclosure $39.

2. Serial output-add $2.00 Note: If you already have this teletype keyboard you can have the kit without it for $36.00 (reg. $39.85). Dealer inquires invited.

This is a great kit for engineers and companies who don't have access to a Teletype. It is a low-cost teaching, learning, and developing tool for hobbyists, professors, students, and electronics entrepreneurs of all levels.

National's new Keyboard Kit now gives SC/MP Kit users a low-cost input/output capability. This new kit replaces the Teletype* normally required by the SC/MP Kit and allows users to evaluate the SC/MP CPU and to develop a variety of application software.

The heart of SC/MP Keyboard Kit is a ROM firmware package (512 bytes) called SCMPKB. The SCMPKB ROM replaces the "Kit Bug" ROM originally supplied with the SC/MP Kit and allows the effective use of the hexadecimal keyboard, to execute programs, to examine or modify the contents of memory and the SC/MP registers, and to monitor program performance.

There is a hole pattern for additional integrated circuits on the SC/MP Kit PC card. By following the simple instructions in the SC/MP Keyboard Kit users manual, one can add buffers, decoders, drivers, multiplexers, etc. Simply replace the Kit Bug ROM (supplied in the SC/MP Kit) with the new SCMPKB ROM, connect the preassembled Keyboard cable connector to the kit card, and you are ready to go!

National's Keyboard Kit comes complete with manual, all required integrated circuits resistors, keyboard display cable connector assembly, wire wrap connectors, precut wires—even a hand-held wire wrap tool.

SWITCHES

10 Position rotary switch by oak manuf. $ 1.00 per 4

8 position, 1 off switch in TOS can $.69 2 for $1.00

«p

ROCKER SWITCH

SPST normally open contact rating 6A 250VAC solder $ .50 ea $2.00 per 6

MINIATURE TOGGLE SWITCH

SPST P.C. MOUNT $.99

MINIMUM ORDER $5.00

Shipping & Handling:

KEYBOARD or SC/MP - $3.00 + $.50 Insurance

all others -$1.00

California residents add 6% sales tax.

ELECTRONICS WAREHOUSE Inc.

1603 AVIATION BLVD.

REDONDO BEACH, CA. 90278

TEL. (213)376-8005

WRITE FOR FREE CATALOG You are invited to visit our store at the above address

World's Lowest IC Prices

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MEMORIES

Rams

2102 1.50*

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7400

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7407

.20

7410

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7420

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7427

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7438 7440 7441

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7445

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7447

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7450

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7451

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7480

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74107

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74116

74123

74141

74145

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74151

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74152 74155 74157 74160 74161

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9602

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74S01

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74S37

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74S197

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.40

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HIGH SPEED

74H00

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74H01

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74H04

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74H10

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74H11

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74H40

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74H51

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74H52

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74H74

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74H103

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74H106

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SCHOTTKY

74LS00

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74LS27

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74LS174

74LS175

74LS193

74LS221

74LS251

74LS253

74LS257

74LS258

CMOS 4001 4002 4006

.29

.29

.29

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.65 1.10 1.10 1.10 1.50* 1.50 1.50 1.10* 1.50 1.50 1.50* 1.50 1.50 1.50 1.50

.16*

.16

.90

4007 4008 4011 4012 4013 4015 4016 4019 4020 4021 4023 4024 4025 4027 4028 4030 4040 4042 4043 4044 4049 4050 4066 4068 4069 4071 4073 4075 4516 4528 4585

LINEARS

NE536T

NE555V

NE556A

1456V

1458 V

566V

567V

540L

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.90

.95

.16*

.75

.20*

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.60

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.95

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.75

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.65

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.16

.16

.16

.16

.85

.75

.85

2.75

.43

.90

.75

.52 1.25 1.35 2.00

Order Minimum $10.00. Add $1.00 shipping and handling charge per order. California residents add 6°o sales tax. All orders shipped First Class within 24 hours.

Order the famous lasis 6 volume Programmed Learning Course "Microcomputer Design is a Snap" for $99.50 and receive a special $10.00 credit on any group of IC's.

Satisfaction 100% guaranteed.

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PO BOX 2542 B Sunnyvale, CA 94087

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OVER TWO YEARS OF EXPERIENCE SELLING *tK X 8 BOARDS HAS SHOWN US EXACTLY WHAT YOU WANT IN A MEMORY BOARD KIT.

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74LS0O

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$0

IT

k

36

74LS01

0

36

74LS02

0

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0

42

74LS08

0

38

74LS10

0

36

74LS11

0

38

74LS14

1

38

74LS20

0

36

74LS21

0

38

74LS22

0

38

74LS27

0

38

74LS30

0

36

74LS32

0

38

74LS37

0

S3

74LS38

0

53

74LS42

1

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74LS74

0

56

74LS75

0

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74LS109

0

60

74LS124

2

SU

74LS125

0

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74LS126

0

7$

74LS132

1

50

74LS138

1

38

74LS139

1

38

74LS155

1

38

74LS157

1

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74LSI60

1

85

74LS161

1

8b

74LSI62

1

85

74LSI63

1

85

74LSI68

1

87

74LSI69

1

87

74LSI 74

1

38

74LSI75

1

35

74LS221

1

38

74LS240

1

88

74LS257

1

25

74LS258

1

Si

74LS273

2

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74LS283

1

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74LS367

1

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74LS368

1

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74LS377

1

88

74LS378

1

38

S1LS95

1

13

81LS96

1

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81LS97

1

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S1LS98

1

13

We Now Distribute Knowledge!

We are happy to carry the Adam Osborne & Associates series of books on microcomputers, as lucid and complete a treatment of the subject as we've seen to date. All books postpaid in the USA; set of all three books available for only $25.00.

VOL 1 "An Introduction to Microcomputers" Order book #2001. Gives the basics of uP based systems $7.00

VOL 2 This recent addition gives up-to-date information on microprocessors equivalent to hundreds of

pages of data sheets. Order book #3001 $12.50

VOL 3 "8080 Programming for Logic Design" #4001 $7.50

a@@isni?3© mm &T*

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. 25 PIN RS-232 /^"V°V°°"-^7^\ CONNECTORS: sub*—C^EJj^W^ mini 0 type.

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Female jack, part #DB25S $3.95

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Now you have a choice—specify wire wrap pins (illustrated) or soldertail with .250" row spac ing. For IMSAI and Altair peripherals. Wire wrap part # S-100WW. Soldertail part # S-100ST.

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3 level, gold plated

14 pin 10/$3.70

16 pin 10/53.85

18 pin. l/$0.75

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40 pin 1/$1.75

CRYSTALS

WE OFFER TWO DIFFERENT TYPES OF CRYSTALS--

STATEK XTALS: ,0t| accuracy in a T0-5 can. Excellent

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SENTRY XTALS: Series mode, fundamental, wire leads. Choose from 4, 5, 8, 9, 10, 12, 15, 18, and 20 MHz. (Note: 18 MHz=8080 clock, 4 MHz=PACE clock freq.)

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The tip of the iceberg:

This page is just a sampling of what you'll find in our latest flyer...we also carry Vector products, like their 8800V prototyping board, their beautiful new Vector-Pak enclosures, and helpful tools like the Slit-N-Wrap and Wiring Pencil...not to mention Vectorboard and all their useful little terminals. Then there are our chip sets... other kits...power supplies ... components...the latest TTL...CMOS,..if you want to get plugged into a great source of parts that delivers from stock, send for our flyer.

BILL GODBOUT ELECTRONICS BOX 2355, OAKLAND AIRPORT. CA 94614

TERMS

TERMS: No CODs; Cal res add tax. Add 50c to orders under $10; over $10 add 5% handling/shping. Call (415) 562-0636, 2h ^rs, to place BankAmericard* or Mastercharge® credit card orders.

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SM74154N SN74155N SN74156N SN74157N SN74160N SN74161N SN74163N SN74164N SN74165N SN74166N SN74167N SN74170N SN74172N SN74173N SN74174N SN74175N SN74176N SN74177N SN74180N SN74181N SN74182N SN74184N SN74185N SN74186N SN74187N SN74188N SN74190N SN74191W SN74192N SN74193N SN74194N SN74195N SN74196N SN74197N SN74198N SN74199N SN74200N SN74279N SN74251N SN74284N SN74285N SN74367N

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CMOS

CD4035 CD4040 CD4042 CO4044 CD4046 CD4047 C04049 CO4050 CD4051 CD4053 CO4060 C04066 CD4069 CO4071 CD40B1 CD4511 CD4518 CD4b66 74COON 74C02N

2.50 2.50 3.00

74C04N

74C10N

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74C74

74C90N

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74C160

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74C164

74C173

74C193

74C195

MC4044

MC14016

3 25 300 3 25 260 2.75 2.75 4.50

LM301H

LM301CN

LM302H

LM304H

LM305H

LM307CN

LM308H

LM30BCN

LM309H

LM309K

LM310CN

LM311H

LM311N

LM318CN

LM319N

LM320K-5

LM320K-5.2

LM320K-12

LM320K-15

LM320T-5

LM320T-5.2 1.75

LM320T-8

LM320T-12

LM320T-15

LM320T-18

LM32QT-24

LM323K-5

LM324N

LM339N

LM340K-5

LM340K-6

LM340K-8

LM340K-12

LM340K-15

LM340K-18

LM340K-24

LM340T-5

LM340T-6

LM340T-8

LM340T-12

LM340T-15

LM340T-18

LM340T-24

LM350N

LM351CN

1 00

1 00

1.35

1 75

9.95

1.95 1.95

LINEAR

LM370N

LM373N

LM377N

LM380N

LM380CN

LM381N

LM382N

NE501K

NE51QA

NE531H

NE536T

NE540L

NE550N

NE555V

NE560B

NE561B

NE5628

NE565H

NE565N

NE566CN

NE567H

NE567V

LM703CN

LM709H

LM709N

LM710N

LM711N

LM723H

LM723H

LM733N

LM739M

LM741CH

LM741CN

LM741-14N

LM747H

LM747N

LM748H

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LM1303N

LM1304N

LM1305N

LM13G7N

LM1310N

LM1351N

LM1414M

LM1458C

LM1496N

LM1556V

LM2111N

LM2901N

LM3065N

LM3900N

LM3905M

LM3909

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MC5558V

LM7525N

LM7535N

8038B

LM75450

75451CN

75452CN

75453CN

75454CN

75491CN

75492CN

75494CN

RCA LIN CA3013 CA3032 CA3035 CA3039 CA3046 CA3059 CA3060 CA3080 CA3081 CA3082 CA3083 CA3086 CA3089 CA3091 CA3123 CA3130 CA3140 CA3600 RC4194 RC4195

2.15 256 2.48

74LSOO 74LS02 74LS03 74LS04 74LS05 74LS08 74LS10 74LS13 74LS14 74LS20 74LS26 74LS27 74LS?H 74LS30 74LS32 74LS40 74LS51 741^55 74LS73

^74LS00 TTL

74LS74 74LS75 74LS76

74LS83 74LS85 74LS86 74LS90 74LS92

74LS95

74LS96

74LS107

74LS109

74LS112

74LS132

74LS136

74LS138

74 US 139

74LS151

74LS153

741S157

74LS162

74LS163

74LS164

74 US 175

74LS181

74LS190

74LS191

74LSI92

74LS193

74LS194

74LS195

74LS257

74LS260

74LS279

74LS670

MM5309 MM5311 MM5312 MM5314 MM5316 MM5318 CT7001

CLOCK CHIPS

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FTK0020 FTK0021 FTK0022 FTKOG23

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10 Red LED Lamps

5 Mixed Colored LED Lamps

10 LEO Mounting Clips

5 Three Piece LED Mounting Adapters

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MAN 1 MAN 2 MANS MAN 4 MAN 7 MAN 7G

POLARITY

Common Anode 5 x 7 Dot Matrix Common Cathode Common Cathode Common Anode Common Anode-green Common Anode-yellow Common Anode-green Common Anode-red Common Anode Common Cattiode Common Anode-yeliow Common Cathode-yellow

MAM 3620

MAN 3640

MAN 4710

DL701

DL704

DL707

DL 728

DL747

DL750

DL338

FNO70

FND503

FNO507

POLARITY

Common Anode-orange Common Cathode-orange Common Anode-Red Common Anode-red * Common Cathode Common Anode Common Cathode Common Anode Common Cathode Common Cathode Common Cathode Common Cathode Common Anode

8 {tin

16 pin 18 pin 22 pin

14 pin 16 pin 18 pin 24 pin

16 pin

IC SOLDERTAIL — LOW PROFILE (TIN) SOCKETS

5-49 50-100 _,^^_ T

35 SOLDERTAIL STANDARD (TIN)

28 pin 36 pin 40 pin

SOLDERTAIL STANDARD (GOLD)

28 ptn 40 pin

WIRE WRAP SOCKETS (GOLD) LEVEL #3

. Plastic Push Button Switch

• 18 AWG Solid Wire - 5" Long

' .50 (wide) X .60 (high) H-27 Thread

' 8 AMP @ 14 Volt -1 AMP @ 110 Volt

1-9 10-Up J-188-1 Push On-Push OH 59 ,49 J-188-2 Normally Open .59 49

J-188-3 Normally Closed .59 49

MINATURE TOGGLE SWITCH

on/off/on $1.95

on/none/on $1.75

on/off/on $1.50

on/none/on $1.25

CLIPLITE NEW LED M0UNTING SYSTEM — to be used

with XC556 LEOS — SPECIFY COLORS — 8/S149

♦SPECIAL* RED _ GREEN - AMBER — yellow '*

50 PCS.

ASST. 1

ASST. 2

ASST. 3

ASST. 4

ASST. 5

ASST. 6

ASST. 7

ASST. 8R

RESISTOR ASSORTMENTS $1.75 PER ASST

68 OHM 82 OHM 100 OHM 120 OHM

180 OHM 220 OHM 270 OHM 330 OHM

470 OHM 560 OHM 680 OHM 820 OHM

1 2K 1 5K 1 8K 2 2K

3 3K 3 9K 4 7K 5 6K

8 2K 10K 12K 1SK

470K

1 2M 3 3M

22 OHM

56 OHM

150 OHM

390 OHM

1K

2 7K

6 8K

120K 330K 820K 2 2M

5 6M

1/4 WATT 5% 50 PCS.

1/4 WATT 5% 50 PCS

1/4 WATT 5% 50 PCS.

1/4 WATT 5% SO PCS.

1/4 WATT 5% 50 PCS.

1/4 WATT 5% 50 PCS

1/4 WATT 5% 50PCS.

Includes Resistor Assortments 1-7 (350 PCS.) $10.95 ea

Send 24c Stamp lor 1977 Catalog

1021-A HOWARD AVE., SAN CARLOS. CA. 94070

PHONE ORDERS WELCOME — (415) 592-8097

All Advertised Prices Good Thru March

WIRE WRAP CENTER

HOBBY-WRAP TOOL-BW-630

$34.95 W

Battery Operated (Size C) Weighs ONLY 11 Ounces Wraps 30 AWG Wire onto Standard DIP Sockets (0.25 inch) Complete with built-in bit and sleeve.

WIRE-WRAP KIT — WK-2-W WRAP • STRIP • UNWRAP

• Tool for 30 AWG Wire

• Roll of 500 ft. White 30 AWG Wire

• 50 pes. each 1", 2", 3" & 4" lengths pre-stripped white wire

$11.95

WIRE WRAP TOOL WSU-30

WRAP ♦ STRIP • UNWRAP $5.95

WIRE WRAP WIRE — 30 AWG

25ft. min. $1.25 50ft. $1.95 100ft. $2.95 1000ft. $15.00 SPECIFY COLOR — White - Yellow - Red - Green - Slue - Black

THUMBWHEEL SWITCHES

SERIES SA Htw Mmih Aw»tty

mm mm

Sf_EP ' Ene

.sf-pp ; cWi

SFHB " Hall

Permacel Electrical Tape

• % ' (wide) X 66 ft (long) • All weatfter • Not Import $1.49 par roll — $12.50 par 10 n

TYPE 1N746 1N751A

1\752 1N753 1N754 1N959 1N965B 1N5232 1N5234 1N5235 1N5236 1N456 1N458 1N485A

mm

1N4002 1N4003 1N4004

ZENERS

VOLTS W

3 3 400mm

5 1 400m

5.6 400m

6.2 400m

6.6 400m

8 2 400m

15 400m

5.6 500m

6.2 500m

68 500m

7 5 500m

25 40m

150 7m

180 10m

50 P1V 1 AMP

100 PIV 1 AMP

200 PIV 1 AMP

400 PIV 1 AMP

DIODES —

PRICE TYPE

4/100 1N4005

4/1 00 1N4006

4/1.00 1N4007

4/1 00 1N36O0

4/100 1N4148

8/1.00 1N4154

4/100 1N4305

28 1N4734

28 1N4735

28 1N4736

28 1N4738

6/1.00 1M4742

6,1 00 1N4744

6/1 00 1N11B3

12/1 00 1N11B4

12 100 1N1185

12:1.00 1M186

12-1.00 1N1188

RECTIFIERS

VOLTS W

600 PIV 1 AMP 800 PIV 1 AMP 1000 PIV 1 AMP 50 200m

75

35

10m

PRICE

10 1 00 101 00 10/1.00

6/1 00 15/1 00 12/1.00 20/1 00 28 28

12 t*

15 1*

50 PIV 35 AMP

100 PIV 35 AMP

150 PiV 35 AMP

200 PfV 39 AMP

400 PIV 35 AMP

SCR AND FW BRIDGE RECTIFIERS

C36D C38M 2N2328 MDA 980-1 MOA 980-3

15A@400V 35A @ 200V 1.6A @ 200V 12A @ 50V

12A (5) 200V

MPSA05 MPS A06 2N2219A 2N2321 JN222JA

FN241S 2N2464 2N2906A 2N2907A 2N2925 2N3053 2N3055 MJE3055

5:^1.00 5/S1 00 3«1 CO 411 00

5.11 OC S/S1 00 4/S1.00

tm oo

4/s: oo1 4i%\ 00

tm oo

511 00 2 V 00 S 89 SI 00 St 25

tm oo

5.11.00

RANS

ISTORS

PH4249

411 00

PN4250

4.11.00

PN3567

3/S1.00

2N44O0

4.11.00

PN3568

411 00

21W401

411 OO

PN35S9

41100

2H4402

411 00

2N37CM

5/S1.00

t 2N4403

411.00

3W3705

511.00 M

L 2N4409

511.00

2N3706

511 OO T

' 2N5086

411 00

2N3707

511 00

2K5067

411 00

2N3711

511 OO i

2MS088

411.00

?N3,V.l

S 65 I1

i 2N5089

411.00

S! 00

2N5129

511 00

2N3903

511 OO

2K513S

Ml 00

2N3904

411 00

2N5139

511 00

2N3905

411 00

2N5209

5.11 00

2N3906

411.00

2N5951

511 00

2M4013

3.11 00

C106B1SCR

211 00

2N40M

311 00

2N5432

S2.00

2N4123

1011.00

CAPACITOR

10 pf

22 pf

47 pf 100 pf 220 pf 470 pf

OOlmf .0022 0047mf

.01mf

T35V 15'35 V .22/35V -33/35V .47/35V .68/35V 1.0/35V

47/50V 1.0/50V 3.3/50V . 4.7/25V 10/25V 10/50V 22/25V 22/50V 47/25V 47/50V 100/25V 100/50V 220/25V 220/50V 470/25V 1000/16V 2200/16V

» VOLT CERAMIC DISC CAPACITORS

10-49 50-100 .04 03 OOVF 04 .03 0047MF .04 03 OVF 04 03 022^F 047MF

CORNER

1-9 10-49 50-100

04

.035 1,xF

10 VOLT MYLAR FILM CAPACITORS

022mf 047mf

Imt

.27

.17

23

.07 22mf 33 .27

D TANTALUMS (SOLID! CAPACITORS 17 1.5/35V 30 26

.17 2.2/25V .31 .27

.17 3.3/25V .31 27

17 4.7/25V .32 28 .17 6.8/25V 36 .31

17 10/25V .40 35

.17 15/25V .63 50

» ELECTROLYTIC CAPACITORS

10

.47/25V 47/50V 1.0/16V 1 0/25V 1.0/5OV 4.7/16V 4 7/25V 4.7/50V

10/16V

10/25V

1 0:50V

47/50V 100/16V 100/25 V 100/50V 220/16V 470/25V

.15

20 18

30 28

.17 .18

28 .26

r

£ CRYSTALS fr

CY1A CY2A CY3A CY7A CY12A CY14A CY19A CY22A CY3O0

THESE FREQUENCIES ONLY

' Frequency Case Style

1.000 MHz 2 000 MHz

4 000 MHz

5 000 MHz

10 000 MHz 14 31818 MHz 18.000 MHz 2C 000 MM? 32.000 MHz

HC33/U HC33'U HC18/U HC18/U HCIB'U HC18U HC18/U HC18/U HC1B-U

$5,95 $5 95

S4.95 $4.95 S4 95 $4 95 $4 95 $4.95 $4 95

XR-2260KB Kit $27.95

XR 2206KA Kit $17.95

XR 205

XR-2206CP

XP.22Q7CP

STEREO

m 131OCP

XR 1310EP XR 1800P XR-2567

EXAR

S3 20 3 20 320

XR-555CP S i9

XR-320P 1 55

XR-556CP 1 B5

XR-25S6CP 3 20

XR-2240CP 3 25 PHASE LOCKED LOOPS

XR-2!0 5 20

XR-215 6 60

XR-567CP 1 95

XR-567CT 1 70

CONNECTORS

PRINTED CIRCUIT EDGE-CARD

.156 Spacing-Tin-Double Read-Out Bifurcated Contacts — Fits .054 to .070 P.C. Cards

15/30 PINS (Solder Eyeiet) 51.95

18/36 PINS (Solder Eyelet) $2.49

22/44 PINS (Solder Eyeiet) $2.95

50/100 (100 Spacing) PINS (Solder Eyelet) $6.95

25 PIN D SUBMINATURE

DB25 PLUG $3.25

DB25 SOCKET $4.95

3V2 DIGIT DVM KIT

This 0-2 VDC 05 per cent digital voltmeter features the Motorola Vh digit DVM chip set ft has a .4" LEO display and operates from a single +5V power supply The unit is provided complete with an injection molded black plastic case complete with Bezel An optional power supply is available which fits into the same case as the 0-2V DVM allowing 117 VAC operation

A. 0-2V DVM with Case $49.95

B. 5V Power Supply $14.95

VECTOR WIRING PENCIL

Vector Wiring Pencil P173 consists ft I iMMf 'M i MtafWfcfN I -inner one ounce! tool which is used to guide and wrap Insulated wire ted oti a self-con(amen -cpiaceaoie bobbin onto component leads or terminals installed on pre-punthed P Partem VeclOfbord Connections between the wraoped Wire and componem leads pads or terminals are made by soldering Complete with 250 FT ol red wire CQ QC

MICROPROCESSOR COMPONENTS

8080A CPU $19.95 MC68O0L 8 Bit MPU S35.00

8212 8 Bit Input/Output 4.95 MC6820L Periph. Interface Adapter 15.00

8216 Bi-Oirectiona! Bus Driver 6.95 MC6810AP1 128 x B Static RAM 6.00

8224 Clock Generator/Driver 10.95 MC6830L7 1024 x 8 Bit ROM 18.00

8228 System Controller - Bus Driver 10.95

2504 2518 2519 252'! 2525 2527 2529 2532 2533 3341 74LS670

CPUS

e sit cpu

Super 8008 Super 8008

SfiS 1024 Dynamic He* 32 BIT Hex 40 BIT 512 Dynamic 1024 Oynamic Dual 256 BIT Dual 512 BIT Quad 80 BIT 1024 Static Fifo 16 « 4 Reg

AY-5-1013 30K8i

2513 2516

74S387

REPLACEMENT WIRE — BOBBINS FOR WIRING PENCIL

W36-3-A-Pkg 3 250 ft 36 AWG GREEN $2.40

W36-3-B-Pkg 3 25C ft 36 AWG RED $2.40

W36-3-C-Pkg. 3 250 ft 36 AWG CLEAR S2.40

W36-3-D-Pkg 3 250 ft 36 AWG BLUE $2.40

1/16 VECTOR BOARD

fPOXY GLASS

0 1 Hole Spacing Pan No

64P44 062XXXP 169P44 02XXXP

r,.; ',: ;iK 84P44 062 169P44 062 169P84 062

169P44 062C1

6.50

1/00 650 8 50

**

HEAT SINKS

205-CB Beryllium Copper Heat Sink «

291-.36H Aluminum Heat Sink tor TO-: 680- 75A Black Anooized Aluminum

|£

h Black Finish tor TO 5 $ .25

0 Transistors 4 ftegulalor $ .25

$1.60

HEXADECIMAL ENCODER 19-KEY PAD

j£|&fc

• ABCDEF

• Return Key

• Optional Key I Period)

• - Key

$10.95 each

any kind of PC B A very solid

molded plastic 13 x 4 base suits most apDlicatmns

$19.95

HDQt&S 16 LINE TO FOUR BIT PARALLEL KEYBOARD ENCODER

JOYSTICK

These joysticks feature four * potentiometers, that vary resistance proportional to the angle of the stick. Sturdy metal construction with plastics components only at the movable joint. Perfect for electronic games and instrumentation

*5K Pots $6.95 *100K Pots $7.95

Char Gen

Char Gen

1024-Bit Programmable

S19.95 24 95 19 95

4 00 2.49 6 00

5 9 95

10.95

2101 2102 2107 2111 7010 7489 8101

91L02 74200 93421 MM5262

1702A 5203 82S23 82S123

74S287 3601

256 x 1 1024 x 1 256x4 1024 x 1 4096 x 1 256 x 4 1024 x 1 16 « 4 256x4 256 x 4

WW'S

Static Dynamic Static Static Dynamic Static MNOS Static Static Static Static Static Static Static Dynamic PROMS

OpenC

Tnstate

St.itic Fast

S 2 25

2 49 6 95 fi K

) '.H

2 U I BS

? <h

6330-1 6331-1 6300-1 6301-1 6305-1

'Sptcial Programing Available

256 Bit 132 x ■ Open Collector 256 Bit (32 x 8) Three State 1024 Bit (256 x 4) Open Collector 1024 Brt (256 x 4) Three State 2048 Brt (512 x 4) Open Collector

- BIPOLAR PROM SPECIAL - Write or Call tor Pricing'

it (512 x 4) Three State it (512 x I Open Collector .il (512 x B) Three State it (102 x 4) Open Collector it (1024x4) Three State

6306-1 6340-1 6341-1 6352-1 6353-1

2048 Brt {I 2048 Bit <! 2048 Bit 8 4096 Bit (1 4096 Bit (1

19.95 19 95 19 95

Proto Board 100

Continental Specialties $19.95 aaat «*»»*

^ BREADBOARD » ^"^

*■* * BUDGET KIT

%% f „ _, t§

;. 29.95 IMP li

Proto Board 6 $15.95

SPECIAL!

LOGIC M

isplays static and logic States ol DTL TTL " "S DIP ICs Pocknt Da S84.95.

^ ^oitaneousli

*■* dynamic logic

%%. HTL or CMOS D

1™ Pocket sue

OTf*

OT-596 OT 47S OT-47B OT-35S OT 358 OT IBS OTtaS

GEMINI-68 The Unique Microprocessing System

ALL BOARDS BUS EXPANDABLE

Uses standard size 4V2" wide boards, dual 22 pin edge connector Fully buffered and tristatable address and data buses

STAND ALONE CPU BOARD — Has 384 bytes of RAM on board, serial I/O (RS-232

and 20 ma current loop, cycle stealing direct memory access (DMA), built in soft- *n_ft ft_

ware — selectable echo-back capability. Part # SA-CPU Board $279.95

CPU BOARD — Same as above but only has 128 bytes of RAM on board-used with

8K RAM board listed below Part # Gemini 68 CPU Board $259.95

8K RAM BOARD — Uses low power static RAMS, 500ns cycle time, 1.5 Amps Max

Part # Gemini 68 RAM Board $269.95

8K EPROM BOARD — Uses 5204 EPROMS by AMI or NATIONAL. Shipped with all decode and miscellaneous ICs, except the 5204 EPROMS n

Part # Gemini 68 EPROM Board $ 89.95

NOT A KIT — ALL BOARDS ARE COMPLETELY ASSEMBLED, BURNED-IN AND TESTED. COMES WITH COMPLETE DOCUMENTATION.

Allow approximately fou weeks tor deliveiy

$5.00 Minimum Order — U.S. Funds Only California Residents — Add 6% Sales Tax

Spec Sheets - 25c — Send 24c Stamp tor 1977 Dealer Discount Available — Request Pricing

1021-A HOWARD AVE., SAN CARLOS, CA. 94070

PHONE ORDERS WELCOME — (415) 592-8097

All Advertised Prices Good Thru March

DIP SWITCH

These switches lecture seven SPST slide switches in a molded (lip They are ideally suited tor microprocessor

»»":a"0"s S1.95

©Timebcind

DIGITAL ALARM CLOCK $16.95

• 24-Hour Alarm

• ' DOZE Button

• 100% Solid State

• Large Red Led Display (.8" high)

• AM.PM Indicator

• Seconds Display at touch of button

• SPECIFY BLACK OR IVORY

DIGITAL WATCHES

• 6 Function

• Bracelet Styling

• 1 Year Guarantee

$59.95

EXELAR Mens Watch

• 5 Function

• Quartz Crystal

• Black Leather Band

• Manufacturer Guarantee

• Specify Gold or Chrome

$25.00

5 FUNCTION ELECTRONIC CALCULATOR RADOFIN MODEL 8P

$8.95

FUTURES

• 8 Digit Display

• 5 Functions consists of addition subtraction, multiplication division percentage, with constant on all functions with full floating decimal point

• Power source is 1 piece 9V DC Battery 00GP tack tor AC adapter

• Slack superfine grained finish plastic cabinet

DIGITAL STOPWATCH

• Bright 6 Drgrt LED Display

• Times to 59 minutes E>9 59 seconds

• Crystal Continued Time Base

• Three Stopwatches in One

Times Single Event — Split & Taylor

• Size4 5'x2 15 x 90 (4'?ouncesi

• Uses 3 Pentite Cells

Kit - $39.95

Assembled — S49.95 Heavy Duty Carry Case $5.95

DIGITAL QUARTZ CAR CLOCK

•■pi'

Kit: $29.95 Assembled: $39.95

, i_nt; (K M tiom mounting biacket of the miection molded case down to the thiee conductor power CO id and all component rn fiuding MM5314 Clock chip Features quartz accuracy ol 0l°c sn digit 35 high LEO display and PC Boards Works on any 1? volt system — motorcycles, boats vans motorhomes autos and trucks

DIMENSIONS 4'? x 4 >? 12oi 24 HOUR MODE

CASE ONLY (includes hardware, mounting; bracket and bezel) $5.95

115 VAC

JE700 CLOCK

The J£ TOO is I low cost digital clock but is a very high quality unit The unit tealures a simulated walnut case with di menstons o( 6 x 2'i x 1 N utilizes I MAN72 high brightness readout, and thi MMWU dock chip

$17.95

This large digit clock (6" hours & minutes. 3' seconds) f eatu res the MM5314 clock chip. It operates from 117 VAC. and will operate in either a 12 or 24 hour mode. The dock is complete with a walnut grain case, and has fast set. slow set. and hold time set features

JE500 KIT - ALL COMPONENTS & CASE $34.95 WIRED & ASSEMBLED 539,95

DIGITAL CLOCK KIT — 3Vz INCH DIGITS

4 DIGIT KIT $49.95 4 DIGIT ASSEMBLED S59.95

6 DIGIT KIT $69.95 6 DIGIT ASSEMBLED $79.95

This clock features big 3V?" high digits for viewing in offices, auditoriums, etc Each digit is formed by 31 bright 0.2" LED's. The clock operates from 117 VAC, has either 12 or 24 hr. operation The 6 digit version is 27" 3Vi" x IVj" and the 4 digit is 18" x 3VT x 1'/?" Kits come complete with all components, case and transformer.

Specify 12 or 24 Hour When Ordering

JE803 PROBE

The Logic Probe is a unit which is tor the most part /

indespensible in trouble shooting logtc families ^

TTL OTL RTL CMOS It derives the power it •"«w**^t|

needs to operate dnectly oft of the circuit under

test drawing a scant 10 mA max it uses a MANS

readout to indicate any of the following states by

these symbols (H) - 1 iLOWl ■ o (PULSE)-P The »ft -_ p y..

Probe can delect high liequency pulses to J5 MHz ^3.33 rCI MI

It can 1 be used at MOS levels or circuit damage

win result printed circuit board

PL 5V 1A Supply

This is a standard TTL power supply using the well known LW36SI m ■■■■■'"• ' te provide a solid 1 AMP ol current at 5 volts We try to make things easy tor you by providing everything you need in one package, including the hardware for only

$9.95 Per Kit

SPECTRA FLAT TWIST

50 conductor, 28 gauge, 7 strands/conductor made by Spectra. Two conductors are paired & twisted and the flat ribbon made up of 25 pairs to give total of 50 conductors. May be peeled off in pairs if desired. Made twisted to cut down on "crosstalk." Ideal for sandwiching PC boards allowing flexibility and working on both sides of the boards. Cost originally $12.00/ft.

SP-234-A $1.00 ft 50cond. 10 ft/$9.00 SP-234-B .90ft32cond. 10ft/$8.00

WIRE WRAP WIRE

TEFZEL blue #30 Reg. price $13.28/100 ft. Our price 100 ft $2.00; 500 ft. $7.50.

MULT! COLORED SPECTRA WIRE

Footage 8 Cond.

12 "

14 "

29 "

#24 22 22 22

10' $2.50 3.00 3.50 7.50

50'

9.00

11.00

13.00

28.00

100'

15.00 18.00 21.00 45.00

Great savings as these are about 1/4 book prices. All fresh & new.

VIATRON cassette tape deck as shown $35.00

Set of 2 read/write, amplifiers & servo control boards for deck $40.00

VIATRON full spare set of 11 microprocessor boards, checked out $200.00

COM ADAPTER kit RS-232C will run any baud rate 110-1200 BPS. TTL logic and UART

w/diagram, control panel for Viatrbn & cable $90.00

COM ADAPTER as above fully assembled & tested, panel, cables $150.00

VIATRON large tape deck, 7 bit ascii, 9 track, 800 BPI w/power supply cables, control panel,

tape, instructions $375.00

AM-FM solid state w/power supply for 115 volts AC. Has mike input, stereo tape or record player input, built-in loop stick. Ready to use, just add speakers $10.00

CREDIT VALIDATER

Made for feeding into a computer terminal to query the credit balance of a customer with push-button entry and audio response. Power supply in separate case attached to base may be removed to use for other projects should you wish to scrap. Regular 115 volt input and output of plus 5 volts and plus & minus 12 V both DC & regulated. The phone is touch pad style, automatic electric pad. All sold "as is" 2 PC boards inside jammed with various parts & ICs including memory. Uses buffers ICs to accelerate & decelerate call traffic. Inquiry from Validier emerge as short bursts of Binary data signals. Normally used over leased phone lines at 200 times the capacity of messages. All appear to be excellent & complete. A Computer gadgeteers SPECTACULAR. And at a crazy price of only $18.00. 2 for $35.00

Ship. wgt. 101b. #SP-153-AL ea $18.00

PARITY DETECTOR

New packaged, made for RCA, detects even or odd parity, baud rate 110, 150 or 134.46. Built-in logic supply for the ICs, operates from standard 115 Vac. Control panel allows manual or automatic reset mode of operation. Aluminum enclosure (not shown) covers the electronics. TTY compatible. Ship wt 10 lbs.$12.50

#

r*&*TfT

Please add shipping cost'on above.

FREE CATALOG SP-9 NOW READY

P.O. Box 62, E. Lynn, Massachusetts 01904

The prokoboard from BIM...

$14

2/$25

TOP QUALITY

$28

HEAVY

DUTY

POWER

TRANSFORMER

FOR

IMSAI/ALTAIR

5VDC ;

@ 22A J

#18VDC |

40V I

(Prom programming)!

m

» electr*^rti^«-

INCLUDE APPROX SHIPPING

Check or money order only- Calif, residents 6% tax. AH orders postpaid in the U.S. $10 Min. order. Prices subject to change without notice.

the jyroko electronics shoppe

439 marsh st. san luis obispo, ca, 93401 805/544-5441

The Proko Paper Tape Reader: A manually operated reader, reads 9-leve! paper tape into any parallel input port. Just supply a light source, grab the tape and pull!

KIT $42 Assemb. $55

KITS BY CYBERCOM A DIVISION OF SOLID STATE MUSIC

| EDGE CONNECTORS

80 Pin WW .125" used $1.50 ea. 10/12.50 86 Pin Soldertail .156" $3.75 ea. 10/$32 I 100 Pin spec WW or Soldertail both fit IMSAI or SSM Mother Bd $5.00 ea 10/$44

82S06 82S07 82S11 82S12 82S17 82S23 82S123

2.00 82S126

2.00 82S129

2.00 82S130

2.00 82S131

2.00 74S206

2.50 74S412

3.00 74S301

3.50 3.50 3.95 3.95 2.10 4.00 3.50

74C200

8573

8574

8575

8576

8577

8578

5.50 4.50 5.50 4.50 4.50 3.50 4.00

7400 7401 7402 7403 7*404 7405 7406 7407 7408 7409 7410 7411 7413 7414 7416 7417 7420 7423 7425 7426 7427 7430 7432 7437 7438 7440 7441 7442 7443 7444 7445 7446 7447 7448 7450 7451 7453 7454 7460 7470 7472

.16 7473

. 16 7474

.21 7475

.16 7476

.18 7480

.24 7483

.20 7485

.29 7486

.25 7489

.25 7490

.18 7491

.30 7492

.45 7493

70 7494

.35 7495

35 7496

.20 74100

.37 74107

.30 74109

.30 74121

.35 74122

.25 74123

.30 74125

27 74126

.27 74132

15 74141

85 74145

.60 74147

75 74148

.75 74150

.75 74151

.80 74153

.70 74154

.80 74155

.25 74156

25 74157

.25 74160

20 74161

20 74162

.45 74163 .40

.35 .35

.50

.30

.50

.70

.90

.40

2.00

.45

.75

.50

.50

.80

.75

.90

1.00

.40

.90

.40

.50

.70

.60

.60

1.00

1.15

1.15

2.35

2.00

1.00

.80

.90

1.00

1.00

1.00

1.0C

1.2L

1.00

1.50

1.00

74164

74165

74166

74170

74173

74174

74175

74176

74177

74179

74180

74181

74182

74184

74185

74190

74191

74192

74193

74194

74195

74196

74197

74198

74199

74200

74251

74284

74285

74365

74367

74368

MH0025

MH0026

95H90

2102-1

32

64

1488

1489

1.10

1.10

1.25

2.10

1.50

1.95

.95

.90

.90

.90

.95

2.50

.95

1.95

2.20

1.15

1.25

.90

.90

1.25

.75

1.25

.90

1.75

1.75

4.95

1.75

4.95

4.95

.90

.75

.90

2.50

2.95

9.95

1.65

50.00

96.00

1.50

1.50

I4KX8 Static Memories i

ImB-1MK-8 board, 1 usee 2102 or eq. PC Board $221

(Kit $83 I

JMB-2 Altair 8800 or IMSAI compatible Switched address .

|and wait cycles. PC Board $25 .

.4 Kit (91L02A .5 usee).... $129.95 j

■MB-4 Improved MB-2 designed for 8K "piggy-back" I

I without cutting traces. PC Board $301

J Kit 4K .5 usee $129.95 Kit 8K .5 usee $1991

I MB-3 1702A's Eroms, Altair 8800 & imsai 8080 compat-I ible Switched address & wait cycles. 2K may be ex-

■ panded to 4K. Kit less Proms $65 2K Kit $145

"j 4K Kit $225 ]

I MB-6A8Kx8 Switched address and wait assignments! I Memory protection is switchable for 256, 512, 1K, 2K, 4K I land 8K. 91L02A .5 usee rams, Altair 8800 & IMSAI I

8compatible. With battery power option I

Kit $250 Assembled & tested $290 \

il/O Boards '

■TyO-21/0 for 8800, 2 ports, committed pads for 3 more, I jother pads for EROMS UART, etc. !

64 x 16 VIDEO BOARD Altair plug compatible display 32 x 16 or 64 x 16 switch selectable. Composite and| parallel video ports, upper and lowercase with software. Kit $179.9!

Misc

Altair compatable mother board. Room for 15 connec-) tors 11" x HV2" (w/o connectors)....*..$45 With 15 connectors $111.00

Altair extender board (w/o connectors) $9

With w/w connector $13.50

..$47.50 PC Board only $25

MODEMS

1702A*EROM

1702A* 2 usee

*programming send hex list

AY5-1013UART

2513 prime spec, upper or

lowercase 8080A prime CPU 8212 prime latch buffer 8224 prime clock gen 8228 prime sys control ler

$85.00 $10.00 8.00 5.00 | $6.95 j

11.00

25.00 4.00 5.00 8.90

MM1402A MM1404A MM5006A MM 5013 MM5015A MM5016 MM 5017 MM 5025 MM5026 MM 5027 MM 5053 MM 5054 MM 5055 MM 5056 MM 5057 MM 5058 MM5314 MM5316 MM 5320 MM5554 MM 5555 MM 5556

1.90 1.90 1.50 2.50 1.50 1.50 1.90 2.50 2.50 2.80 1.50 1.90 1.90 2.80 2.80 3.50 4.00 4.50 5.95 1.90 2.50 2.50

2501B

2503V

2504V

2505K

2507V

2509A

2510A

2511A

2517V

2518B

2519B

2521V

2522V

2525V

2527V

2528V

2529V

2532B

2533V 91L02APC 32 each 64 each

$1.25 2.00 2.00 2.00 1.25 2.00 2.00 2.80 1.25 1.50 2.80 1.50 2.00 2.80 2.80 2.80 2.80 2.80 2.80 2.55 2.40 2.25

1101

1103

2101

2102-1

2111-1

2112

2602

4002-1

4002-2

MM 5260

MM5261

MM 5262

7489

74200

74S89

74C89

74L89

8223

F4702

1.25 1.25 4.50 1.65 4.50 4.50 1.60 7.50 7.50 1.00 1.00 1.00 2.00 4.953.50 3.50 3.50 2.50 17.00

(baud rate gen) 2.4576 MHZ Crystal 8.95

74LS00

74LS01

74LS02

74LS03

74LS04

74LS05

74LS10

74LS11

74LS12

74LS20

74LS22

74LS27

74LS30

74LS42

74LS55

74LS73

74LS74

74LS76

74LS151

74LS174

74LS175

74LS192

.40 .50 .40 .40 .45 .45 .40 .50 .55 .40 .45 .45 .40 1.50.40 .65 .65 .65 1.55 2.20 1.95 2.85

74L0O 74L01 74L02 74L03 74L04 74L05 74L06 74L08 74L09 74L10 74L20 74L26 74L30 74L32 74L42 74L51 74L54 74L55 74L71 74L73 74L74 74L75

.25 .25 .25 .25 .30 .40 .30 .40 .40 .30 .35 .40 .40 .45

1.50 .35 .45 .35 .30 .55 .55

1.20

74L78

74L85

74L86

74L89

74L90

74L91

74L93

74L95

74L98

74L123

74L154

74L164

74L165

74L192

74L193

MC4044

N8264

N8263

N8826

DM8131

8T37

8T10

.90 1.40

.75 3.50 1.50 1.50 1.70 1.70 2.80 1.50 2.00 2.50 2.50 1.25 1.20 2.25 3.50 3.50 2.50 2.50 2.50 2.00

90 Day Guarantee on SSM Products. Kits MB-2, MB-3 (2K OR 4K), MB-4, MB-6, 10-2 video board and mother board with connectors may be combined for a discount of 10% in quantities of 10 or more. This supercedes the flier of 13 Sept. 1976.

MIKOS

419 Portofino Dr. San Carlos, Ca. 94070

For large orders please send money order or cashiers check to avoid delays in waiting for checks to clear.

Check or money order only. Calif, resident 6%tax. All orders postpaid in U.S. All devices tested prior to sale. Money back 30 day guarantee. Sorry we can not accept returned IC's that have been soldered to. $10 min. order. Prices subject to change without notice.

Thinly disguised affiliates of KO Electronics and Surplus, S.L.O., CA 93401

S.D. SALES CO.

P.O. BOX 28810-B DALLAS, TEXAS 75228

Z-80 CPU CARD KIT FOR IMSAI/ALTAIR

$149:

From the same people who brought you the $89.95 4K RAM kit. We were not the first to Introduce an IMSAI/ALTAIR compatible Z—80 card, but we do feel that ours has the best design and quality at the lowest price.

The advanced features of the Z—80 such as an expanded set of 158 Instructions, 8080A software compatibility, and operation from a single 5VDC supply, are all well known. What makes our card different is the extra care we took in the hardware design. The CPU card will always stop on an Ml state. We also generate TRUE SYNC on card, to insure that the rest of your system functions properly. Dynamic memory refresh and NMI are brought out for your use. Believe It or not, not all of our competitors have gone to the extra trouble of doing this.

As always, this kit includes all parts, all sockets, and complete Instructions for ease of assembly. Because of our past experience with our 4K kit we suggest that you order early. All orders will be shipped on a strict first come basis. Dealers inquiries welcome on this item.

Kit shipped with 2 MHZ crystals for existing 500NS memory. Easily modified for faster RAM chips when the prices

come down.

Kit includes Zilog Manual and all parts.

JUMBO LED CAR

CLOCK

$16.95

KIT

You requested it! Our first DC operated clock kit. Professionally engineered from scratch to be a DC operated clock. Not a makeshift kiuge as sold by others. Features: Bowmar 4 digit .5 inch LED array, Mostek 50252 super clock chip, on board precision time base, 12 or 24 hour real time format, perfect for cars, boats, vans, etc. Kit contains PC Board and all other parts needed (except case). 50,000 satisfied clock kit customers cannot be wrong!

FOR ALARM OPTION ADD $1.50 FOR XFMR FOR AC OPERATION ADD $1.50

60 HZ CRYSTAL TIME BASE FOR DIGITAL CLOCKS S.D. SALES EXCLUSIVE!

KIT FEATURES:

A. 60HZ output with accuracy comparable to a digital watch.

B. Directly interfaces with all MOS Clock Chips. ^

C. Super low power consumption. (1.5 ma typ.) $5.95 Of

D. Uses latest MOS 1 7 stage divider IC. 2/$10.

E. Eliminates forever the problem of AC line glitches.

F. Perfect for cars, boats, campers, or even for portable clocks at ham field days.

G. Small Size, can be used in existing enclosures.

KIT INCLUDES CRYSTAL, DIVIDER IC, PC BOARD PLUS ALL OTHER NECESSARY PARTS & SPECS

50HZ CRYSTAL TIME BASE KIT - $6.95

All the features of our 60HZ kit but has 50HZ output. For use with clock chips like the 50252 that require 50HZ to give 24 hour time format.

1

THIS MONTH'S SPECIALS!

300.00 KHZ CRYSTAL - $1.50

8080A - CPU CHIP by AMD - $19.95

82S129 - 256 x 4 PROM - $2.50

N.S. 8865 OCTAL DARLINGTON DRIVERS

3 for $1.00

Z-80 - CPU by ZILOG - $69.95

MM5204 - 4K EPROM - $7.95

Prices in effect this month ONL Y!

s

4K LOW POWER RAM BOARD KIT THE WHOLE WORKS - $89.95

Imsai and Altair 8080 plug in compatible. Uses low power static 21 L02—1 500ns. RAM's, which are included. Fully buffered, drastically reduced power consumption, on board regulated, all sockets and parts included. Premium quality plated thru PC Board.

7400—19c 7411—29c 74LS00—49c 7413—50c 7402—19c 7416—69c 74LS02—49c 7420—19c 7404—19c 7430—19c 74L04—29c 7432—34c 74S04—44c 7437—39c 74LS04-49C 7438—39c 7406—29c 7440—19c 7408—19c 7447—85c 7410—19c 7448—85c TTL INTEGRATED CIR

7451—19c 7453—19c 7473—39c 7474—35c 74LS74-59C 7475—69c 7476—35c 7480—49c 7483—95C 7485—95c 7486—45c CUITS

7490—65c 74153 74LS90—95c 74154

7492—75C 7493—69c 7495—75c 7496—89c 74121-38C 74123-65C 74132-1.70 74S138-1.95 74192 74141-75C 74193 74195

74157

74161 74164 74165 74174 74181 74191

-75c 1.00 —75C -95c 1.10 1.10 -95 c 2.50 1.25 1.25 1.00 —69c

Z-80 Manual - $7.50 Separately.

STICK IT!

in your clock

in your DVMf etc.!

Huge Special Purchase

Not Factory Seconds

As sold by others!

$3.95

4 JUMBO .50"

DIGITS ON

ONE STICK!

(with colons and

AM/PM Indicator! BUY 3 for $10.

BOWMAR 4 DIGIT LED READOUT ARRAY

The Bowmar Opto-Stick. The best readout bargain we have ever offered. Has four common cathode jumbo digits with all segments and cathodes brought out. Increased versatility since any of the digits may be used independently to fit your applications. Perfect for any clock chip, especially direct drive units like 50380 or 7010. Also use in freq. counters, DVM's, etc. For 12 or 24 hour format.

UP YOUR COMPUTER!

21L02-1 1K LOW POWER 500 NS STATIC RAM

TIME IS OF THE ESSENCE!

And so is power. Not only are our RAM'S faster than a speeding bullet but they are now very low power. We are pleased to offer prime new 21L02—1 low power and super fast RAM's. Allows you to STRETCH your power supply farther and at the same time keep the wait light off. 8 for $12.95

$19 QR S.D. SALES EXCLUSIVE! <J10 QC

gi^"JJ MOS 6 DIGIT UP-DOWN COUNTER * IA*W

40 PIN DIP. Everything you ever wanted in a counter chip. Features: Direct LED segment drive, single power supply {12 VDC TYP.), six decades up/down, pre-loadable counter, separate pre-loadable compare register with compare output, BCD AND seven segment outputs, internal scan oscillator, CMOS compatible, leading zero blanking. 1MHZ. count input frequency. Very limited qty. WITH DATA SHEET

WESTERN DIGITAL UART

No. TR1602B. 40 pin DIP

This is a very powerful and

popular part.

NEW-$6.95 with data

LIMITED QUANTITY

V p

RESISTOR ASSORTMENT

% W 5% and 10%

PC leads. A good mix

of values. 200/$2.

1702A2K ERASEABLE PROM'S - $6.95

We tell it like it is. We could have said these were factory new, but here is the straight scoop. We bought a load of new computer gear that contained a quantity of 1702 A's in sockets. We carefully removed the parts, verified their quality, and are offering them on one heck of a deal. First come, first served. Satisfaction guaranteed! U.V. Eraseable. $6.95 each 4 for $25

TERMS: Money Back Guarantee. No COD. Texas Residents add 5% tax. Add 5% of order for postage and handling. Orders under $10. add 75c. Foreign orders: US Funds ONLY!

SLIDE SWITCH ASSORTMENT

Our best seller. Includes miniature and standard sizes, single and multiposition units. All new, first quality, name brand. Try one package and you'll reorder more, SPECIAL 12/$1.

MOTOROLA POWER DARLINGTON Back in Stock!

Like MJ3001, NPN 80V. 1 0A. HFE 6000 TYP. TO-3 case. We include a free 723C volt reg. with schematic for power supply. SPECIAL —$1.99

CALL YOUR BANK

AMERICARD OR MASTER CHARGE ORDER IN ON OUR CONTINENTAL

UNITED STATES TOLL FREE WATTS:

1-800-527-3460

Texas Residents Call Collect

214/271-0022

S.D. SALES CO. P.O. BOX 28810 B Dallas, Texas 75228

For orders over $15. 00 Choose $1. 00 FREE tndse.

F8 EVALUATION BOARD KIT WITH EXPANSION CAPABILITIES

A fantastic bargain for only

• 20 ma of RS 232 interface

• 64K addressing range

• Program control timers

• 1K off on board static memory

$99

with the following features:

00 • Built in clock generator

• 64 Byte register

• Built-in priority interrupts

• Documentation

GENERAL PURPOSE COMPUTER POWER SUPPLY KIT

This power suppy kit features a high frequency torroid transformer with switching transistors in order to save space and weight. 115V 60 cycle primary. The outputs with local regulators are +5V at 10A, -5Vat1A, ± 12V at 1 A.

$79

00

UNIVERSAL 4K X 8 MEMORY BOARD KIT

$74

50

This memoryboard kit can be used with most microcomputers. Some of the outstanding features are:

32-2102-1 static RAM's, 16 address lines, 8 data lines in, 8 data lines out, all buffered. On board decoding for any 4 of 64 pages.

4K F8 Basic $25.00

2708 PROM $55.00

2522 STATIC SHIFT RE6 - $1.95

2518 HEX 32 BIT SR $3.50

2102 1 1024 BT RAM S1.80

5280-4K DYNAMIC RAM $10.50

5202A UV PROM S10.50

MM5203 UV PROM $10.50

1 702A UV PROM $10.75

5204-4K PROM $18.95

MINIATURE MULTI-TURN TRIM POTS 100, 500, 2K, 10K, TOOK, 200K, 1 Meg.

S.75 each 3/S2.00

MULTI-TURN TRIM POTS Similar to Bourns 3010 style 3/16"x5/8"x1-1/4"; 50, 100, 1K, 10K, 50K ohms

$1.50 eti . . . .3/$4.00

LIGHT ACTIVATED SCR's

TO-18. 200V 1A . S 1.75

TRANSISTOR SPECIALS

2N3585 NPN Si TO-66 $ .95

2N3772 NPN Si TO-3 $ 1.60

2N4908 PNP Si TO 3 S T .00

2N6056 NPN Si TO 3 Darlington , $ 1.70

2N5086 PNP Si TO-92 4/$ 1.00

2N4898 PNP TO-66 $ .60

2N404 PNPGETO-5 5/S 1.00

2N3919 NPN Si TO-3 RF $ 1.50

MPSA 13 NPN Si TO 92 3/S 1.00

2N3767 NPN Si TO-66 $ 70

2N2222 NPN Si TO-18 ....... 5/S 1.00

2N3055 NPN Si TO-3 $ .80

2N3904 NPN Si TO-92 5/$ 1.00

2N3906 PNP Si TO-92 5/S 1.00

2N5296 NPN Si TO-220 $ .50

2N6109 PNP Si TO 220 $ .55

2N3638 PNP Si TO-5 5/S 1.00

2N65I 7 NPN TO 92 Si 3/$ 1.00

C/MOS (DIODE CLAMPED)

74C02- .22 4015 95 4035-1.10

74C10- .22 4016- .40 4042- .78

74C193 1.50 4017-1.05 4047-2.00

4001- .22 4018-1.00 4049- 40

4002- .22 4019 25 4050- .40 4006-120 4022- .95 4055 1.50 4007- .22 4024 .75 4066- .80

4009- .42 4027- .40 4071- .22

4010- .42 4028 .88 4076- .70

4011- .22 4029-1.10 4081- .22

4012- .22 4030- .22 4520-115

4013- .40

MCA 81 OPTICAL LIMIT SWITCH SI 50

LED READOUTS

FND 500-.5" CC $1.75

HP7740-.3"C.C $1.40

MAN-7-.3" C.A $1.25

NS 33-3 dig. array $1.35

PL 747 $2,50

Send 25f;for our catalog featuring

Transistors and Rectifiers

145 Hampshire St. Cambridge Mass.

Terms: FOB Cambridge, Me! Send Check Include Poe Order $5.00, C(

7 WATT LD-65 LASER DIODE IR $a95

PRINTED CIRCUIT BOARD

4 1/2 x6-1/2 SINGLE SIDED EPOXY

BOARD 1/16" thick, unetcheri

£.50 ea 5/S2.20

2N 3820 P FET . . $ .45

2N 5457 N FET $ .45

TIS43UJT $ .35

ER 900 TRIGGER DIODES .. 4' $1.00

2N 6028 PROG. UJT $ .65

8 PIN DIP SOCKETS $ .24

14 PIN DIP SOCKETS S .25

16 PIN DIP SOCKETS $ .28

18PIN DIPSOCKETS S .30

24 PIN DIP SOCKETS $ .40

40 PIN DIP SOCKETS S .60

VERIPAX PC BOARD This board is a 1/16" single sided paper epoxy board, 4'//'x6'," DRILLED and ETCHED which will hold up to 21 single 14 pin IC's or 8, 16, or LSI DIP IC's with busses for power supply connector. ....... $400

MV 5691 YELLOW-GREEN

BIPOLAR LED $1 25

FP 1 00 PHOTO TRANS S .50

RED, YELLOW, GREEN OR

AMBER LARGE LED's . . . ea. $ .20

MOLEX PINS 100/$1.00

1000/S7.SO 10 WATT 2ENERS3.9.4.7, 5.6,8.2, 12, 15,

18, 22, 100, 150 or 200V . . . ea. S .60 1 WATTZENERS 4.7, 5.6, 10. 12, 15,

18 OR 22V ea. S .25

MC6860 MODEM CHIP $13.00

TANTULUM CAPACITORS

Full Wave Bridges

Si icon Power Rectifiers

PRV

1 A

3A

12A

50 A

125A

100

06

.14

.30

.80

3.70

200

.07

.20

.35

1.15

4.25

400

.09

.25

.50

1,40

6.50

600

.11

.30

.70

1.80

8.50

800

ts

.35

.90

2.30

10.50

1000

20

45

1 10

2 75

12 50

47UF 35V 5<$1 00 68UF 35V5/S1.00 1UF35V 5/S1 00 2.2UF 20V5/S1 00 3.3UF 35V4/S1.00

6.8UF 35V3/S1.00 22UF 35V S .40 33UF 35V $ .40 30UF 6V 5/S1 00 100'JF 35V S .50 I50UF 15V $ .50

M/001 ALARM CLOCK CHIP.

$5.75

NATIONAL MOS DEVICES

MM 1402- 1.75 MM1403- 1.75 MM 1404- 1.75 MM5013- 2.50 MM5016-2.50 MM5017- 2.70 MM5055- 2.25 MM5056- 2.25

MM5057-2.25 MM5058-2.75 MM5060- 2.75 MM5061- 2.50 MM5555- 4.75 MM5556- 4.75 MM5210- 1.95 MM5260- 1.75

SILICON SOLAR CELLS

2%" diameter at 500 ma. ... $4.00 ea., 6/$22.50

REGULATED MODULAR POWER SUPPLIES

+ - 15 VDC AT 100ma

115VAC INPUT S2/.95

5VDC AT 1A. 115VAC INPUT . . . $24.95

12 VDC AT .5 AMP $24.95

IN 4148 (IN914) , 15/51.00"

7400

7401

7402

7403

7404

7405

7406

7407

7408

7409

7410

741 1

7412

7413

7414

7416

7417

7420

7425

7426

7427

7430

7432

7437

7438

7440

7441

TTLIC

7442744574467447744874507472747374747475747674807483748574867489 749074917492749374947495749674107741 21 7412374125

SERIES

52 74126.70 74151.70 74153.70 74154.70 74155.20 7415733 7416135 7416474165

74173

74174 74175 74177 74180 74181 74190 741917419274193741947419574196 7425774279 7532475491 /mm:'

.30 1.85

.95 1.05 1.40

2.10

1.20 1.20

MINIATURE DIP SWITCHES

CTS-2064

Four SPST switches

in one

minidip package.

$1.75

CTS-206-8

Eight SPST switches

in a 16

pin DIP

package

$1.95

AY-5-1013-A30K ser./par., par./ser., universal UART $6.95

ALCO MINIATURE TOGGLE SWITCHES

MTA 106 SPOT $1.20

MTA 206 DPDT . . $1 .70

SOLID STATE SALES

P.O. BOX 74B

SOMERVILLE, MASS. 02143 TEL. (617) 547-4005

200

.75

1.25

2.00

400

.95

1.50

3.00

600

i :>n

1.75

400

SAN KEN AUDIO POWER AMPS

Si 1 010 G 1 0 WATTS $ 7.95

Si 1020 G 20 WATTS SI 5.95

Si 1050 G 50 WATTS. $27.95

CCD 110 LINEAR 256 XI BITSELF SCANNING CHARGED COUPLED

DEVICE $99.00

CCD 201 100 x 100 CHARGE COUPLED DEVICE ..... $135.00

LINEAR CIRCUITS .

LM307 - -Op. Amp * .30

LM309K 5V 1A REGULATOR .. S .95

723 - 40+ 40VV RFGULATOR . . $ .50

301/748-Hi Per. Op. Amp $ .31

320T 5,1 2,1 5, or 24V N EG R EG . . S 1.25

709C Op. Amp $ ,31

741 A or 741 C OP AMP $ ,31

710 COMPARATOR . S ,35

CA 3047 Hi Pet. Op. Amp S .95

340T 5, 6, 8, 12, 15, 18, 24V POS

REG. TO-220 . $1.10

101 OPER. AMP. HI PERFORM. . . S 75

LM 308 Opei. Amp., Low Power . . S .95

747 DUAL 741 $ .65

556 - DUAL TIMER S1.00

537 - PRECISION OP. AMP. .... S1 70

LM 3900 - QUAD OP. AMP ... S .49

LM 324 - QUAD 741 SI .50

560 - PHASE LOCK LOOP .... S2.00

561 - PHASE LOCK LOOP . . . S2.00

565 - PHASE LOCK LOOP . . . . ' S1.25

566 FUNCTION GEN SI.65

567 - TONE DECODER $?.50

LM 131 ON FM STEREO DEMOD. . $2 75

8038 IC VOLTAGE CONT. OSC. . S3.90

LM 370 - AGC SQUELCH AMP. . SI.15

555 - 2jus - 2 HR. TIMER S .45

553 QUAD TIMER S2.50

FCD810OPTO-ISOLATOR .... S .80

1458 DUAL OP AMP S .60

LM 380 2W AUDIO AMP S .95

LM 377 - 2W Stereo Audio Amp. . S2.50

LM381 - STEREO PREAMP. . . . SI.50

LM 382 - DUAL AUDIO PREAMP SI.50

LM 311 - HI PER. COMPARATOR S .90

LM319 - Dual Hi Speed Comp. . . SI.25

LM 339 - QUAD COMPARATOR S1.50

WE SHIP OVER 95%

OF OUR ORDERS THE

DAY WE RECEIVE THEM

• Accuracy +0.05% of Reading +1 Count

• Two Voltage Ranges 1.999 V and 199.9 mV

• Up to 25 Conversions/*

• Zin> 1000 M ohm

• Auto-Polarity and Auto Zero

• Single Positive Voltage Reference

• Standard B Series CMOS Outputs-Drives One Low Power

Schottky Load

• Uses On Chip System Clock, or External Clock

• Low Power Consumption: 8.0 mW typical @ ±5.0 V

• Wide Supply Range: e.g.. ±4.5 V to ±8.0 V

MC14433 SINGLE CHIP 3|DIGIT A/D

Single chip combines linear and CMOS digital to bring you the simplest yet DVM approach. Requiring only 4 external passive parts, this subsystem gives you: Auto polarity, auto zero, single voltage reference, 8 mW operation, overrange, underrange signals, 25 conversions per second and .05% 4 1 count accuracy! 100 uV resolution, 24 Pin DIP. MC14433P with specs $1 9.55

MCI4412 UNIVERSAL MODEM CHIP MCI4412 contains a complete FSK modulator and de-modulator compatible with foreign and USA communications. (0-600 BPS) FEATURES:

.On chip crystal oscillator . Echo suppressor disable tone generator .Originate and answer modes

.Simplex, half-duplex, and full duplex operation .On chip sine wave .Modem self test mode .Selectable data rates: 0-200 0-300 0-600 .Single supply VDD=4.75 to 15VDC - FL suffix VDD=4.75 to 6 VDC - VL suffix TYPICAL APPLICATIONS:

.Stand alone - low speed modems .Built - in low speed modems .Remote terminals, accoustic couplers

MC14412FL.... - $28.99

MC14412VL $21.74

6 pages of data .60

Crystal for the above $4.95

MCI4411 BIT RATE GENERATOR. Single chip for generating selectable frequencies for equipment in data communications such as TTY, printers, CRT s or microprocessors. Generates 14 different standard bit rates which are multiplied under external control to IX, 8X, 16X or 64X initial value. Operates from single +5

volt supply. M044»t.......... „ $11.98

4 pages of data.. ■ ... 40

Crystal for the above $4.95

REMOTE CONTROL TRANSMITTER. MC14422P is a 22 channel ultra-sonic remote control transmitter I.C. CMOS uses little power and only a few external passive components. Applications include TV receivers, security controls, toys, industrial controls and locks. 16 pin DIP plastic pkg. MC14422P with specs $11.10

MC6525 REMOTE CONTROL RECEIVER

The MC6525 is a 22-channel remote control receiver circuit designed for uss in television receivers, industrial remote controls, remote security controls, radio receivers, electronic games and similar applications. The circuit is intended for use with ths MCI4422 remote control transmitter. Comes in 28 pin DIP plastic package. MC6525P. with 6 pages of specs $18.38

3 DECADE (BCD) COUNTER CHIP MC14553BCP consists of 3 negative edge triggered synchronous counters, 3 quad latches and self scan multiplexed , TTL compatible outputs.

MC14553BCP $8.72

Spec sheets $.60

,LM1889 TV VIDEO MODULATOR

The LM1889 is designed to interface audio, color difference and luminance signals to the antenna terminals of a TV receiver. It consists of a sound subcarrier oscillator, chroma subcarrier oscillator, quadrature chroma modulators, and R.F oscillators and modulators for two low-VHF channels. The LM1889 allows video information from VTR's, games, test equipment, or similar sources to be displayed on black and white or color TV receivers. LM1889 with 16 pages of data $9.95, data only, $1.00

m?Gta?

Says

IF YOUR PROJECT TIME AND MONEY ARE BEING BLOWN AWAY BY DELAYS AND HIGH PRICES— ****** MARCH ON DOWN TO TRI-TEK! ********

okmachine

ANB TOOL CORPORATION

HOBBY WRAP TOOl

HOBBY-WRAP TOOL

Battery operated with built-in 30 ga bit and sleeve. , Uses standard C batteries (not included). Light weight,! only 11 oz. Wraps standard DIP sockets. Has built in device to prevent overwrapping . Pistol grip, positive indexing. Quality construction assures exceptional

performance. BW-630 $34.95

FREE, a 50' roll of wire wrap wire with each tool If I

TL430CLP PROGRAMMABLE ZENER

Brand new device type allows you to make your own zener by external programming. Turn those cheap fixed voltage regulators into rock solid adjustable by adding this little feller, 1 resistor and a pot. Use for min/max indicators, settable crowbar, shunt regulator, clamp. Be the first one on your block to use this new and interest' ing part

TL430CLP $1.00

Specs and applications 30$

93S41 SUPER FAST 4-BIT ALU All 16 possible logic operations on two variables plus arithmetic. Shottky diodes on Input for high speed. Same as 74S181. 93S41 $1 .98, 4/$6.00

DATA BOOKS BY NATIONAL SEMICONDUCTOR

DIGITAL. Covers TTL, DTL, Tri-State, etc $3.95

LINEAR. Covers amplifiers, pre-amps, op-amps... $4. 25 LINEAR APPLICATIONS VOLUME I. Dozens of application notes and technical briefs covering the use of op-amps, regulators, phase locked loops and

audio amps $3.25

LINEAR APPLICATIONS VOLUME II. Takes up where Volume I left you—All the latest linear devices. Along with Vol I you have a great source of app- ■ licatlon data on the most widely used devices as well

as new types just appearing $3.25

CMOS Gates, Flip Flops, registers, etc $3.00

VOLTAGE REGULATORS. A must for anyone making a power supply. Complete theory including transformers, filters, heat sinks, regulators etc $3.00

MEMORY. Info on MOS and Bipolar memories, RAMS

ROMS, PROMS and decoder/encoders $3.95

INTERFACE. Covers peripheral drivers, level translators, line driver/receivers, memory and clock drivers,

sense amps, display driver and opto-couplers $3.95

SPECIAL FUNCTIONS DATA BOOK. Contains detailed Information for specifying and applying special amplifiers, buffers, clock drivers, analog switches and

D/A-A/D converter products $3.25

AUDIO HANDBOOK Contains detailed discussions, including complete design particulars, covering many areas of audio with real world design examples... $3.25

SPECIAL

DATA BOOKSHELF. Buy all ten of the National Data

books at one time and save $5.10!!! $30.00

(All books shipped ppd in US only. Foreign orders please add shipping for 1.5 lbs per book)

HOBBY-WRAP-30 Handy little tool to strip, wrap and unwrap 30 gauge wire $5.95

GILO PLATE'"

COMBINATION LENS AND

MOUNTING DEVICE FOR

T l3/4 LED

xcwwes NO TOOLS

SNAP CLIPLITE

INSERT LEO

AVAILABLE IN TRANSPARENT RED GREEN ■ AMBER CLEAR & YELLOW

MLIPLITE

Combination lens and mounting device for T 1-3/4 LED, The CLIPLITE combines the benefits of the present LED display panel mounting methods and eliminates their deficiencies. Requires no special tools and installs in 6 seconds In .250" hole. Simple two-step installation. Just snap CLIPLITE, Insert LED. Available in transparent red, green, amber, clear and yellow. Specify colors, any mix. 5/$1.00, 10/$1.90, 20/S3.50, 50/$7.50, 100/$13.50

78H12 HIGH CURRENT REGULATOR

Now, a 12V, 5 A regulator in a single TO-3 package I!

Internal short circuit limit and thermal overload protection.

Same ease of application as the popular 309K

78H1 2 with specs $14.25

SN75450 DUAL PERIPHERAL DRIVER

Two identical NAND gates and two 30V, 300mA unconnected NPN transistors in a 14 pin DIP package. Use for

lamp and LED drivers, cable drivers, relays etc.

SN75450N 45$, 10/$3.90

5V, 3Amp O.E.M. Power Supply. Adjustable current limit. Super good specs........ $29.95

FIXED VOLTAGE 1 AMP REGULATORS

+5V In TO-3 98$

+5V in TO-220 Power Tab 95$

+I2V in TO-3 $1.19

+12V in TO-220 Power Tab $1.09

+15 in TO-3 $1.19

+15V in TO-220 Power Tab $1.09

W

tRi-tek, inc.

6522 nopth 43RS Avenue,

Qlen&Ale, ARizonA 85301

phone 602 - 931-6949

We pay surface shipping on all orders over $10 US, $15 foreign in US funds. Please add extra for first class or air mail. Excess will be refunded. Orders under $10, add $1 handling. Please add 50$ insurance. Master charge and Bank America cards welcome, ($20 minimum). Telephone orders may be placed 10AM to 5:30PM daily, Mon thru Fri. Call 602-931-4528. Check reader service card or send stamp for our latest flyers packed with new and surplus electronic components.

fteactep Service

# Reader service inquiries not solicited. Correspond directly with company.

To get further information on the products advertised in BYTE, fill out the reader service card with your name and address. Then circle the appropriate numbers for the advertisers you select from this list. Add a 9 cent stamp to the card, then drop it in the mail. Not only do you gain information, but our advertisers are encouraged to use the marketplace provided by BYTE. This helps us bring you a bigger BYTE.

Reader

Service

Number

75 Advanced Microcomputer Prods 147

173 Anderson Jacobson 143

4 BITS Inc86, 87

153 Bits, Bytes and Pieces 141

* BYTE's Binders 136

200 California Industrial 148

126 Cheap Inc 141

127 Comptek 135

140 Computalker 141 Computer Faire 68, 69

83 Computer Mart NY LI 141

156 Computer Place 143

141 Computer Room 89 208 Computer Shack 83 206 Computer System Design 139 203 Computer Systems 66 197 Computer Systems Center SL 141 199 Computer Transceivers 137 138 Computer Warehouse 149 202 CRC Engineering 133

87 Creative Computing 134

41 Cromemco 1, 2

178 Cybercom 11

185 DAJEN Electronics 66

78 Digital Group 17

210 M W Dunton66 170 ECDCIII

211 Economy Terminal 129 47 Electronic Control Tech 139

157 Electronic Warehouse 150

Reader

Reader

Page

Service

Page

Service

Number

Number

Number

Number

ods147

56

E&L Instruments 95

64

102

Eltron 151

198

9

Godbout152

63

69

HAL Communications 97

*

55

Heath Co 103

194

109

iCOM61

*

12

IMSAI15

213

204

International Data Systems 101

24

15

James 153, 154

167

130

JGM Development Labs 139

201

90

Logical Services 139

26

209

Logic Designs Inc 117

*

124

McGraw-Hill 27

27

18

Meshna 155

169

9

196

Micronics 141

59

77

Micro-Term 131

29

L 141

174

Microtex 139

99

119

Midwestern Sci Inst 138

164

57

Mikos 156

96

112

MiniTerm 67

205

*

MITSCIV, 84, 85

121

62

Morrow 145

82

71

mpi 121

136

132

M&R Enterprises 143

192

171

Mullen 131

32

*

National Computer Conf 132

212

22

National Multiplex 37

193

155

North Star Computers 93

137

I

40

Ohio Scientific Instr 33

154

Number

Oliver Audio Engineering 139

Omni 103

Parasitic Engineering 129, 133

PerCom Data 96

Peripheral Vision 81

Polymorphic Systems 25

Prime Radix 127

Processor Technology 5, 6, 7, 8, 9, 63

Quay 98, 99

Riverside Electronics 105

Scelbi 29

Scientific Research 65

SD Sales 157

Smoke Signal Broadcasting 135

Solid State Sales 158

Southwest Tech CI I

STM 145

Sunny Computer Stores 143

Synchro-Sound Enterprises 79

Szerlip Enterprises 121

Tarbell Electronics 125

Technical Design Labs 49

Technical Systems Consultants 137

Tec Mar 119

TriTek 159

University of Texas 143

US Robotics 143

Vector Graphic 12, 13, 35

Worldwide Electronics 91

ecMe

BYTE's Ongoing Monitor Bex

On BOMB Card, Article No.

ARTICLE

1 Grappel: Give Your Micro Some Muscles

2 Kay: PR-40 Alphanumeric Printer Review

3 Freeman: Cassette Transports for "Roll Your Own"

4 Bremeir-Rampii: Digital Cassette Subsystem, Part 2

5 Frenzel: What's Involved in Kit Building?

6 Burhans: Simplified Omega Receiver Details

7 Buschbach: Inexpensive Joystick Interfaces

8 Price: Flights of Fancy with the Enterprise

9 Ciarcia: Try This Computer on for Size

10 Hogenson: Multiplex Your Digital LED Displays

PAGE

9

18

26

38

50

70

88

106

114

122

BOMB's Best Liked for December: Cybernetic Crayon, Weather Predicting

Thomas A Dwyer and Leon Sweer of the Soloworks Lab at the University of Pittsburgh will share the $100 bonus for the readers' most favored article in December 1976 BYTE, "The Cybernetic Crayon." Michael R Firth takes a $50 prize for "Do It Yourself Weather Predictions," the runnerup. December's contest was the last of the "old fashioned" BOMBs, with voting done by photocopying or tearing out part of the last page. Now you can vote for your favorite articles by using the BOMB card inside this BYTE; just get it in before April 10 1977, the deadline for March entries."

160

-49 HicrMin* titpitv ph

III 4>(ftrt«t I n 12, MftVl

o CCDS03K,

Key Into Maxi-Power <g> Micro-Price

■

Micromind is an incredibly flexible, complete and expandable, hardware/ software, general purpose computer system. You won't outgrow it

Hardware includes an 80 key, softwaredefinable keyboard, I/O interface board, 6500A-series microprocessor (powerful enough for advanced computing), a highdetail graphics and character display processor, power supply, rf modulator, and connections for up to 4 tape recorders plus TV or monitor. An interconnect bus

powerful assembler, a debugger, a file system, graphic routines, and peripheral handlers. We also include dynamic graphic games: Animated Spacewar and Life. ECD's standard Micromind /xM-65 supplies 8K bytes of memory. Additional

32K byte expansion boards and a mapping option give Micromind expandable access to 64 Megabytes. Utilizing softwarecontrolled I/O channels, Micrornind's advanced encoding techniques load data from ordinary tape recorders at 3200 bits per second.

Micromind comes to you ready-to-use, factory assembled and fully tested. Among microcomputers, it has the largest memory capacity and the fastest storage. You're looking at the work of the finest display processor on the market. You won't find a microcomputer with a more powerful CPU. You won't find a computer with a more flexible keyboard. You won't find anything to

touch it at $987.54.

permits 15 additional microprocessors, parallel processing and vastly increased computing power.

System software—including ECD's own notsoBASIC high level language, on advanced error-correcting tape cassettes —provides a word processing editor, a

So, quit the kluge scene and key into Micromind. You'll be a main frame performer, with all the comforts of home. We're not fooling... this is the cat's /ml

ECD CORP. 196 Broadway, Cambridge, Mass. 02139 (617)661-4400

€GD

Mame.

Address.

City/State.

.Zip.

□ Fantastic! Check enclosed: $987.54. shipping paid by ecd

□ BankAmericard □ Master Charge Mass, Resident add 5% Sales Tax

# Expiration Date

Signature

□ Send me your brochure.

Actual unretouched photographs.

Now you can buy an

AltairM8800b or an Aitair

680b computer right off

the shelf. Aitair plug-in

boards, peripherals,

software and manuals

are also available.

Check the list below

for the MITS

dealer in your area.

off the s

ALTAIR COMPUTER CENTER 8105 SW Nimbus Ave. BEAVERTON, OR 97006

COMPUTER KITS (S.F. area) 1044 University Ave. BERKELEY, CA 94710 (415J-845-5300

THE COMPUTER STORE

(Arrowhead Computer Co.)

820 Broadway

SANTA MONICA, CA 90401

<213)-451-0713

GATEWAY ELECTRONICS, INC. OF COLORADO 2839 W. 44th Ave DENVER, CO 80211

(3031-458-5444

COMPUTER SHACK 3120 San Mateo N.E. ALBUQUERQUE, NM 87110 {505)-883-8282; 883-8283

ALTAIR COMPUTER CENTER 4941 East 29th St TUCSON, AZ 86711 {602)-748-7363

ALTAIR COMPUTER CENTER 611 N. 27th St. Suite 9 LINCOLN, NB 68603

(402) 474-2800

COMPUTER PRODUCTS UNLIMITED

2412 Broadway

LITTLE ROCK, AR 72206

(501J-371-0449

ALTAIR COMPUTER CENTER

110 The Annex

5345 East Forty First St.

TULSA, OK 74135

(9181-664-4564

ALTAIR COMPUTER CENTER 57 50 Bintliff Drive HOUSTON, TX 77036 (7131-780-8981

COMPUTERS-TO-GO 4503 West Broad St. RICHMOND, VA 23230

(804)-335-5773

MICROSYSTEMS (Washington, D.C.) 6605A Beckllck Rd. SPRINGFIELD, VA 22150 (7031-569-1110

THE COMPUTER STORE Suite 5

Municipal Parking Building CHARLESTON, W. VA. 26301

(304)-345-1360

THE COMPUTER ROOM 3938 Beau D'Rue Drive EAGAN, MN 66122 (6121-452-2567

THE COMPUTER STORE OF ANN ARBOR 310 East Washington Street ANN ARBOR, Ml 48104

(3131-995-7616

THE COMPUTER STORE, INC, (Hartford area) 63 South Main Street WINDSOR LOCKS, CT 06096

(203}-627-0188

CHICAGO COMPUTER STORE

517 Talcott Rd.

PARK RIDGE, IL 60068

(312)-823-2388

GATEWAY ELECTRONICS, INC. 8123-25 Page Blvd. ST. LOUIS, MO 63130

(314)-427-6116

BYTETRONICS Suite 103 1600 Hayes St. NASHVILLE, TN 37203

(615J-329-1979

THE COMPUTER STORE, INC. 120 Cambridge St. BURLINGTON, MA 01803 (617)-272-8770

ALTAIR COMPUTER CENTER 2 69 Osborne Road ALBANY, NY 12211

<518)-458-6140

THE COMPUTER STORE OF NEW YORK 5 5 West 3 9th St. NEW YORK, NY :0018

(2121-221-1404

THE COMPUTER SYSTEMCENTER 3330 Piedmont Road ATLANTA, QA 30306

(4041-231-1691

MARSH DATA SYSTEMS 5405 B Southern Comfort Blvd. TAMPA, FL 33614

(8i3)-eee-989o

0& OGQKB©

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