197605 Byte Magazine Vol 00 09 Shooting Stars

MAY 1976 $1.50 SHOOTING DS UP= MP-A processor card. A complete microcomputer system on a single card. It features the “Motorola” MC6800 processor. The powerful memory orientated processor that is rapidly becoming the standard ‘of comparison in the industry. Also on this board is the MCM6830L7 Mikbug ROM, MC6810 RAM and the MC14411 baud rate generator, The crystal controlled master clock oscillator and tri-state data bus drivers complete the board. Everything works from a single 5.0 Volt supply. MP-M main memory card. This circuit board contains two blocks of 2,048 words of memory. Each part has its own supply regulator and can operate independently of the other half. The memory chips are the proven reliable 2102 static type. They are capable of cycling fast enough to allow full speed operation of the processor at all times. No waiting for refresh cycles and no problems with “flakey” memories. Only a single 5.0 Volt supply required. MPM: csveein os espe $125.00 Chassis, mother board and power supply. Ano- dized cabinet with perfor- ated cover for cool operation. Ten amp power supply will power fully expanded system of up to six memory cards and eight interface cards. MP-B—Mother Board. .... . $40.00 MP-F—Chassis .......... $30.00 MP-P—Power Supply ..... $35.00 TO A GREAT MP-A. . Si) oe $145.00 MP-C serial control interface. This programmable interface may be used to connect the computer to either a video terminal or TTY current loop system. Directly compatable with either system. No hardware changes. MP... cee eee ees 2 840.00 Sul SSOO Computer System with serial interface and 2,048 words COMPUTER SYSTEM smemor.... $395.00 rm = es eee 1 C1 Enclosed is $395 for my SwTPC Computer Kit [] Send Data H y H Vdd. Cor BAC # 1 Qorme Ex Date. i H : H H H _ | NAME H H vere | sum 6800 Syerem ADDRESS H H CITY STATE Zip i ® j istered trademark oj H MIE Deen Steet i | southwest Technical Products Corp., Box 32040, San Antonio, Texas 78284 Motorola Inc. H CLELL I8K BYTESAVER™ ‘Supplied with one 2704 PROM. containing special software to transfer RAM content to PROM and PROM. to RAM. How to save your programs -- and have a PROM programmer, too Cromemco’s popular BYTESAVER™ memory board gives you two of the most-wanted features in microcomputer work: (1) asimple, easy way to store your computer programs in program- mable read only _ memory (PROM). (2) a PROM memory board with the capacity for a full 8K bytes ECONOMICAL The BYTESAVER™ js both a place and a way to store programs economically. It transfers programs from the non-permanent computer RAM memory to the permanent PROM memory in the BYTESAVER™ . Once your program is in the BYTE- SAVER™ , it’s protected from power turn-offs, intentional or accidental. The PROMs used with BYTESAVER™ are UV erasable and can be used again and again. The BYTESAVER™ itself plugs directly into your Altair 8800 or IMSAI 8080. . PROM PROGRAMMER Many people are surprised to learn that in the BYTESAVER™ you also have your own PROM programmer. But it's so. And it saves you up to hundreds of dollars, since you no longer need to buy one separately. The built-in programmer is designed for the 2704 and 2708 PROMs. The 2708 holds 1K bytes, four times the capacity of the well-known older 1702 PROM (yet cost-per-byte is about the same). The 2708 is also fast — it lets your computer work at its speed without a wait state. And it’s low-powered. With 2708's in all 8 sockets, the BYTESAVER™ js still within MITS bus __ specifications, drawing only about 500 mA from the +8V_ bus. A complement of 2708 PROMs gives the BYTESAVER™ its full 8K capacity. HOLDS LARGE PROGRAMS even need a keyboard. Just set the computer sense switches as instructed in the BYTESAVER™ documentation. Transfer of memory content to PROM (“burning”) takes less than a minute. The BYTESAVER™ software controls computer lights to verify complete and accurate transfer of memory content. The software also programs any of the other 7 PROM positions in the BYTESAVER™ as readily as the first. And when used to __ transfer information from the BYTESAVER™ PROMs to RAM, the special design of the software allows loading a large program such as 8K BASIC in one second. AVAILABLE NOW — STORE/MAIL The BYTESAVER's™ 8K-byte capacity lets you store the larger and more powerful programs. 8K BASIC, for example, easily fits in the BYTESAVER™ capacity of 8 PROMs. One 1K PROM will hold many games such as Cromemco’s DAZZLER-LIFE or DAZZLE-WRITER. NO KEYBOARD NEEDED The BYTESAVER™ comes with special software programmed into a 2704 PROM. This software controls transfer of the computer RAM content to the BYTESAVER™ PROM. So you are ready to go. You don't Cromemeco Specialists in computer peripherals The BYTESAVER™ jis sold at computer stores from coast to coast. Or order by mail from Cromemco. Cromemco ships promptly. You can have the BYTESAVER™ in your computer within a week after your order is received. BYTESAVER™ kit 2... 0. $195 (Model 8KBS-K) BYTESAVER™ assembled . . . . $295 (Model 8KBS-W) Shipped prepaid if fully paid with order. California users add 6% sales tax. Mastercharge and BankAmericard accepted with signed order. One First St., Los Altos, CA 94022 » (415) 941-2967 In This Richard Simpson describes his first Date With KIM, the new product from MOS Technology which comes assem- bled and ready to use. This product, which is the basis of his system, marks the first direct entry of a semicon- ductor manufacturer into the personal systems field. Are different microcomputers equivalent? In n Source, RD Boudinot presents some excellent background information on multiple sources of components and systems, the mixing of products from different manu- facturers and methods of evaluating products for use in a personal com- puting system. Of what use is a nice friendly permanent memory? Dale Eichbauer contributes some ideas on the use of Read Only Memories in Microcom- puter Memory Address Space. T= s mo ae page 8 BUTE Previous articles have covered pro- gramming and uses of some of the simpler fusible link read only memo- ries. But how about erasable ROMs? Roger L Smith provides some More Information on PROMs including a method of programming the widely available 1702 parts. One way to get a hard copy termi- nal is to use a receive only Teletype unit. Using an inexpensive ASCII key- board and a UART circuit, Dr George Haller shows how to Serialize the Bits From Your Mystery Keyboard and achieve the same function as a key- board send receive Teletype for about half the cost. Dissatisfied with toggle switches? Use An Octal Front Panel similar to Herman DeMonstoy’s design to replace toggle switches with an octal keyboard, i ofilanast Wile ET eK seme Ot" +0 cor mc S ys. o— 22 umes 2LINES: LINES 9 Ee r Ske saoreerc, 4 | 7 4 i,” SUNES [ TimiNG AND ALU AND REG. ‘MEMORY AND e "(ara.) [oot] a] saver INTERNAL CONTROL LINES ewe? ro mnours-on oureurs— |sunes, Seater war eect page 60 You'll be SHOOTING STARS in a fascinating logical game when you implement a version of Willard Nico’s program on your computer. On the cover is artist Robert Tinney’s impres- sion of a SHOOTING STARS addict. A simple signal generator might suffice for a radio man, but testing of computers and data communications hardware can require more sophis- ticated equipment. One such item is a Serial ASCII Word Generator such as the design Ronald Finger describes. How do you take advantage of a decade of software experience? One way is to emulate another computer’s architecture as Intersil has done with its IM6100. Robert Nelson describes a “Chip” Off the Olde PDP-8E in this first part of a two part article. Can a computer measure voltages without hundreds of dollars worth of hardware? Of course it can. The secret is to use Microprocessor Based Analog/ Digital Conversion Techniques of the sort described in Roger Frank’s article on a very basic interface. Onc of the keys to creating an assembler is defining exactly what the input source language will look like. An appropriate choice which simplifies writing the assembler will greatly speed up the process of implementing the program. In his article on the subject, Gregory Jewell shows how to Simplify Your Homemade Assembler using techniques which are applicable to most microcomputers. BUTE #9 —t MAY 1976 In the Queue staff — Foreground PUBLISHERS 28 36 38 42 50 70 24 60 74 41, 58 54 56 84 88 96 96 MORE INFORMATION ON PROMs Hardware — Smith SERIALIZE THE BITS FROM YOUR MYSTERY KEYBOARD Hardware — Haller AN OCTAL FRONT PANEL Hardware — DeMonstoy SHOOTING STARS Applications — Nico BUILD A SERIAL ASCII WORD GENERATOR Hardware — Finger MICROPROCESSOR BASED ANALOG/DIGITAL CONVERSION Interface Techniques — Frank Background A DATE WITH KIM New Product — Simpson N SOURCE Systems — Boudinot ROMs IN MICROCOMPUTER MEMORY ADDRESS SPACE Systems — Eichbauer “CHIP” OFF THE OLDE PDP-8/E: THE INTERSIL IM6100 Hardware — Nelson SIMPLIFY YOUR HOMEMADE ASSEMBLER Software — Jewell Nucleus In This BYTE Trends in Applications Letters Classified Ads What's New? Clubs and Newsletters BYTE’s Bugs Puzzle Time, Space Ace Answer Book Review BOMB Reader's Service Virginia Peschke Manfred Peschke EDITOR Carl T Helmers, Jr GENERAL MANAGER Manfred Pesch ke PRODUCTION MANAGER Judith Havey PRODUCTION ASSISTANT Elizabeth Alpaugh CIRCULATION Deborah R Luhrs PUBLISHERS ASSISTANTS Cheryl Hurd Carol Nyland Deena Zealy ADVERTISING Elizabeth Alpaugh Virginia Peschke TYPOGRAPHY Custom Marketing Resources, Inc Goodway Graphics Mary Lavoie Taimi Woodward PHOTOGRAPHY Ed Crabtree Custom Marketing Resources, Inc ART Bill Morello PRINTING Custom Marketing Resources, Inc The George Banta Company ASSOCIATES Dan Fylstra Don Lancaster Harold A Mauch Chris Ryland BYTE magazine is published monthly by BYTE Publica- tions, Inc., 70 Main St, Peter- borough, New Hampshire 03458. Subscription rates are $12 for one year worldwide. Two years, $22, Three years, $30. Second class postage paid at Peterborough New Hamp- shire 03458 and at additional mailing offices. Phone 603-924-7217. Entire contents copyright 1976 BYTE Publica- tions, Inc, Peterborough NH 03458. Address editorial cor respondence to Editor, BYTE, 70 Main St, Peterborough NH 03458, Editorial by Carl Helmers Prognostication is like an operational amplifier sys- tem... A computer system can be used to perform an old task using a new approach which requires less per- sonal effort or work. [This editorial is taken from the text of a talk presented at the recent “World Altair Convention” held by MITS Inc in Albu- querque NM.] Trends in Applications Where is the small computer field headed? In order to talk about the future of small computers and their applications, | have to take on the role of a prognosticator, a pre- dictor of future trends and events, Prognos- tication is an art to which mystical or magical qualities are often attributed, but which in reality is nothing more than a com- bination of reasoning and imagination based upon observation. The injection of imagina- tion about possible trends and developments makes prognostication a bit different from a narrow linear extrapolation of identified trends. The imagination component is heavily influenced by personal values and philosophies, and represents a feedback of oughts and shoulds into the course of events as they develop. Prognostication is thus a method of extrapolating observed current trends into the future coupled with the prognosticator’s opinions of what should be happening. In the terms of the scientist or engineer, prognostication is like an opera- tional amplifier system in which the input signal is the observed set of trends and the feedback network is the prognosticator’s personal philosophy and imagination. For example, in predicting the fate of civilization, if one is a congenital pessimist like the members of the Club of Rome, then the pre- dictions will come out claiming disaster and ruin. If one is an optimist about the expand- ing possibilities created by advancing tech- nology, then a totally different character of prediction will result. When you listen to what | have to say, be warned that | have a definite personal point of view regarding computer technology and its proper uses, and that this shapes the nature of the imagination content and the trends | select to emphasize. A Point of View The point of view from which | build my conceptual model of a possible future state of the computer world is the view that the individual person is the most important component part of the human species. It is an observed fact that every great advance made in scientific progress, every great work of art, and every notable human achieve- ment is the result of the work of individual human beings, whether or not the ultimate source of the idea, work or achievement can be identified. What is true for the notable accomplishments is just as true for the ones 4 which may not be individually recorded in history books, It is the individual human being with responsible self interest at heart who discovers new ways to handle old prob- lems, invents new problems and their solu- tions, creates works of art and leads to an improved way of life. My views of the trends in computing are thus oriented to the ways in which computer systems technology can provide a better and more comfortable exis- tence for you — the individuals who are in the knowledgeable vanguard of the new technology of personal computing. In a sense, one of the most exciting aspects of the present time is the prospect that we — you, |, the rest of civilization — are in the early stages of one of the “golden ages” of the planet’s history, a time when art and science are flourishing throughout the more advanced segments of the civilization, Com- puting is one important characteristic of this current age. What Are Computers Used For? So much for the preface. Just what are computer systems used for? How will the characteristics of these uses develop as a result of the constant improvement of hard- ware and software techniques? At the high- est level, | can identify two major facets of the computer system’s application: e@ A computer system can be used to perform an old task using a new approach which requires less personal effort or work, © A computer system can be used to accomplish new tasks which were pre- viously unattainable without the “intelligence” of the processor with its stored programs and conditional execution. In any given application, there is not neces- sarily a sharp distinction between the two facets of the computer’s use, But this view illuminates two interesting aspects of the technology, and can be used in the analysis of a computer’s importance to an applica- tion. A couple of extreme examples will illustrate what | mean by these facets of computing. A good example of an old task which can be expedited considerably by use of a com- puter system is the personal accounting task of balancing a check book. In the modern Often, the most difficult and expensive aspect of bringing up a working system is getting the data in and out of your computer to peripheral devices. The 3P +S I/O Module offers a practical and simple solution. And, this single, versatile card could very well handle all the input/output needs of your 8800 system. The 3P | S has two 8-bit parallel I/O ports, with full handshaking logic, plus a seria! I/O port with a data TV range that can be set anywhere between 35 and 9600 | terminal ae Shown oe left sus one demonstration of the : total flexibility of the 3P+S. Ley |tape punch] One parallel output port can be used to set up 3 control conditions for both parallel and serial ports, as well 3P+S [ pener aes as for setting the serial |/O baud rate under program ¢ control. One parallel input port is available for polling the it. Input Data flags and External Device flags, and for checking 103 the serial I/O error flags. modem Addressing of the module is selectable to any of keyboard h 64 four-address segments within the range of 256 I/O [er addresses. Add another dimension of flexibility by using either the UART and control port, or the two parallel ports, to occupy the lower two relative addresses. The 3P+ Sis the only module that will allow 1.5 stop bits, required by the old (and less expensive!) model teletypes such as the 15, 28, or 33 TTY’s. Our 59-page descriptive 3P +S Owner’s Manual, with detailed schematics and applications, is available for $4.00 (fully refundable upon purchase of a 3P | S). Kit Prices, with premium grade, low profile IC sockets, $135; without IC sockets, $125. Write Us, for details on our other 6200-Y Hollis Street Emeryville, CA 94608 compatible 8800 plug-in modules. A computer system can be used to accomplish new tasks which were previ- ously unattainable without the “intelligence” of the processor with its stored programs and conditional execution. A computer system is a central requirement for the control of whiz bang hardware and the logical progress of a game - algorithm, American way of life, the check book is one of the most ubiquitous of personal financial instruments, Unless you live dangerously, you balance that check book once a month, whenever the bank statement comes. The method of balancing a check book is a bor- ing procedure which is well defined and nearly universal in its use. By employing a computer system, this boring procedure can be expedited through automation. The method is to use a program with interactive characteristics to enter the data, perform the arithmetic, and — if you have hard copy — give you a record of the transactions on paper. Using such programs, the accuracy of the check book can in general be improved and the time required each month can be considerably reduced. This reduction in time wasted on check books can be put to use in other more enjoyable tasks, thus improving your state of well being and happiness, The essence of this type of a computer applica- tion is use of the system as a ‘‘busywork eliminator,” a term | first heard applied by a long time friend, Ken Hardwick. The busy- work is more efficiently performed through automation, thus minimizing the human demands of the work, An example of the new task which could not previously have been accomplished is provided by every highly automated inter- active game which is developed and run ona computer system. There is no way that you or | could have played Space War or Star Trek, or a host of other games, without a computer to store the logic, the responses and histories of the player’s performance in multiple games. (An aside: One could play the games by manually executing the logic, but that would be an onerous task beyond the patience of most normal people.) Here the computer system is a central require- ment for contro! of whiz bang hardware and logical progress of the game algorithm. With- out a speedy and intelligent little “Maxwell’s demon” to control the flow of electrons, you would be unable to play these games at all. A Short and Incomplete Encyclopedia of Applications The application of a technology such as computer systems by individuals depends upon price reductions to the point where people can afford the systems without going bankrupt. The first major breakthrough in this area was provided by our hosts today, MITS Inc, with the Altair 8800 introduced a mere 15 months ago. To quote the market- ing blurbs, now that the “‘age of the afford- able computer” has arrived, individual appli- cations are possible. Here is a short and incomplete encyclopedia of contemporary 6 applications ideas, the inputs to the prognos- tication process. Relieving Onerous Tasks Here the emphasis is primarily upon the “busywork eliminator” aspect of computer systems; however, in many cases additional functions are added to the basic task to make the result a more comprehensive solu- tion to the problem. April 15 comes in a few short weeks. Have you ever considered the prospect of an automated tax preparation process? The minimal automation is that of bookkeeping and records coupled with the calculational capabilities of your computer. More elabor- ate aids to recovering as much money as possible is the use of your computer to model the various ways of combining deduc- tions and options such as income averaging so that the tax you pay is reduced to the minimum within the currently applicable rules. (You can also pull off a bit of “cyber- crud” intimidation the next time the auditor calls: “Well, sir, my computer is program- med according to your rules, so it must be right.”) One of my major problems is keeping track of my record library. | like to listen to classical music of the 18th, 19th and occa- sionally the 20th centuries. | have a record shelf which is heavily burdened with my col- lection, and no way (outside of imperfect human memory) at present to tell whether | already have a record or not when lamina record store. As a result, my collection has several unfortunate duplications. An even- tual application for my own home computer system will be the generation of a personal record catalog which | can bring with me when | go to record stores for a buying spree. The work involved in setting up a file card version of the system is so large that I'll never do it; but using my computer to keep track of the library, | can automatically generate an updated list after each trip to the record stores around Boston. How many times have you thought about the problem of mailing lists? If you are in- volved in a computer club's newsletter operation, the problem is probably at the forefront of your consciousness whenever the newsletter is mailed; but lists are useful for a number of personal purposes as well. Do you partake in the sending of greeting cards which occurs each year? If you do, automation of the list of card recipients will greatly improve the time efficiency of that operation (although some purists might say it lacks a certain “personal” touch). Mailing lists and files of commonly used addresses Continued on page 90 L You're the captain of a crusading starship against the logic of your “8008” or "8080". Your mission: search-and-destroy, a random number of alien ships, without running out of time, out of fuel, out of ammunition or out of the galaxy. Your galaxy consists of 64 quadrants, in which there are 64 sectors. You must plan your mission to destroy all aliens. But, every time you move you lose a stardate and precious fuel. Don’t run into a roaming star that could damage your ship! And, don’t forget how much fuel your warp factor uses! Suddenly, Condition RED! Alien in sight! But, you don't know how big he is. Fire a phasor or torpedo? He's damaged or destroyed, But, you've used up valuable fuel. Does he fire back? How \4 SCELBE P about the fuel used for your protective shields? Be careful. You're running H) out of time and fuel! But, don't give up hope. There are refueling stations out there. It's your job to maneuver logically, strategically, carefully to complete your mission. Here's the multidimensional microcomputer game you've asked for. It's got everything you need for exciting intergalactic adventure. A total program in book form in machine language, for 4K memory: flow charts, illustrations, and more. The program gives you a new, different game every time. Order your copy of SCELBI's GALAXY GAME BOOK today. Only $14.95 ppd. Use Master Charge. Then blast off on your own mission in the galaxy. COMPUTER CONSULTING ENG. sis, scitcsion, aaianity ajo 0 cnanae witout notice. Prices for U.S. and Canadian delivery at book mailing 1322 Rear Boston Post Road ‘ate. Add $2.50 for each publitation if Priority Air Service (U.S.) desired. Overseas include $5.00 for each publication for Milford, CT 06460 + 203/874-1573 Airmail service. Richard S Simpson 314 Second Av Haddon Heights NJ 08035 oo ——s Photo 1: When you first open your KIM-1 box, you see a thick layer of docu- mentation, including a large wall chart of the system's hardware details, an MCS650X Instruction Set Summary card, KIM-1 User Manual, Programming Manual and Hardware Manual. A/so shown in this picture is the KIM monitor listing copy which must be requested separately and is a must if you are to take advantage of KIM's sub- routines in applications programs, A Date with KIM Here it is! In the November 1975 BYTE, Dan Fylstra reviewed the capabilities of the MOS Technology 6501 microprocessor chip in an article titled “Son of Motorola” (page 56). The article stated that “it will be three to six months before you see (a 6501) designed into a kit..." Well, MOS Tech- nology has gone one better and introduced not a kit, but a completely assembled, tested and warranteed microcomputer with a price tag of only $250! Using the 6502 processor chip (a 6501 with an on-chip clock), the microcomputer features 1 K of RAM, 2 K of ROM containing the system executive, a complete audio cassette interface, a serial terminal interface, 15 bidirectional IO lines, a 23 key keypad and a six digit LED display. This completely assembled one board com- puter has all the programming features of the 6502 at a very competitive price. If you have been hesitating over buying a microcomputer because of the difficulty of assembly and the fear that it won't work when you’re finished, KIM-1 is for you. The only assembly required is to attach six self adhesive plastic feet to the back of the KIM-1 printed circuit board and attach a +5 volt, 1 ampere power supply to the 44 pin edge connector provided. You'll also need a supply of +12V for the cassette interface; but a handful of flashlight bat- teries should work fine since only about 50 mA of +12 V is required, and that only when the interface is being used. The name KIM is an acronym for Key- board Input Monitor. The name really des- cribes the ROM executive routines, not the whole unit, but it’s a pleasant change from the manufacturer’s name followed by a number. It’s also significant that the system derives its name from its software. The KIM-1 board can be operated in one of two modes: using the on board keypad and LED display, or using a serial terminal. The keypad and hexadecimal display is infinitely easier and less error prone than throwing toggle switches and reading results from binary lamps. In fact, for program entry and many simple applications, | prefer the 23 key keypad and bright LED display to my slow, noisy Teletype. The keys have a good, positive “feel” to them (MOS Tech- Photo 2:The KIM-1 proc- essor as it is removed from its box. The MOS Technology product comes in a neat package which has one foam pad- ded and static protected KIM-1 board as its bottom layer. nology should know about such things, since they are a major manufacturer of chips for calculators). The switch in the upper right corner of the keypad puts the machine in single instruction (not single cycle) mode. When the switch is ‘‘on,” each depression of the “GO” button causes a single instruction of your program to be executed. Control is then returned to the executive program in ROM and the contents of all six machine registers (PC, X, Y, S, P, and the accumula- tor) are stored in fixed memory locations where you can easily examine them through the keypad or terminal and then “GO” to the next instruction. This is an important capability, since if you just halt a micro- processor after each instruction there is no way of examining the registers (they’re all inside the chip!). 1 won’t go into any detail on the instruc- tion set (see Dan Fylstra’s article for that) except to say that it is comprehensive. The variety of addressing modes makes complex programming (especially when processing lists) a lot easier. The 6502 architecture has no IO register or IO instructions, so any memory location can become an 10 “port” if you build the hardware for it. KIM comes with a built-in 15 line bidirectional 10 interface. TTL levels are acceptable, of course, and one of the lines can supply enough current (5 mA) to directly drive a power transistor. The manual shows how to use it to drive a small speaker for “‘micro- processor music” programmed in a manner similar to the Kluge Harp of October BYTE (page 14). Each line can be separately pro- grammed for input or output by writing a status word into the correct memory location. The cassette interface is carefully thought out and should be foolproof. Half of the executive ROM is devoted to the cassette interface software, which includes rudimen- tary file management and sophisticated pro- grammed equivalents to UART operation. This software allows multiple dumps to a single cassette. A header written on each output segment allows you to say, in effect, “find me program number 34 on the tape and load it starting at location. . .” A check- sum is stored at the end of each segment and the user is immediately informed if the computed checksum doesn’t match when the tape is read back in. You can even record voice data between segments of digital data —the interface will ignore the voice. This feature could be used to verbally record the instructions for a game and then auto- matically load and run it. Both high and low level outputs are provided to interface with any type of cassette recorder. It’s not a vital feature, but it indicates the care with which the entire system has been thought out. The TTY interface is for a standard 20 mA current loop (figure 1 shows how | modified it for an RS-232 interface). A unique feature of the software is automatic data rate detection. As soon as the system is powered up, the user types a RUBOUT character on his terminal. The software ::) If you have been hesitating over buying a_ micro- computer because of the difficulty of assembly and the fear that it won’t work when you're finished, then KIM-1 is for you. KIM-1 derives its name from the software, a sig- nificant indication of the importance of good user support programs. 20mA CURRENT LOOP TO KIM-L APPLICATION RS- 232 RS-232 CONVERSION CONNECTOR CONNECTOR 4n33 13k 2 2 8 s oaTa ——> Yo a ) ? 7 2K + S_tion 4n33 <— pata 30 2 oR i 4 2 " a» | Figure 1; One way to in- terface KIM-1 with an RS-232 compatible ter- minal is illustrated in this diagram. Opto isolators are used to accomplish the coupling. The RS-232 pins 1, 2 and 3 will be suffici- ent for terminals which do not involve handshaking; on some terminals, pins 5, 6, 8 and 20 of the stand- ard RS-232 plug may have to be tied together lo bypass handshaking sig- nals. calculates the data rate (anything from 110 to 1200 baud is acceptable) and auto- matically adjusts all further conversation to that rate. No additional timing standards or switches are required for the interface. The real beauty of the terminal interface is in the software, not the hardware. On request, MOS Technology supplies a com- plete listing of KIM. All the executive ROM software subroutines are documented and available to the user referencing this well- commented listing. Thus, to print the con- tents of the accumulator in hex on the terminal requires a simple one-instruction subroutine call. Those readers who have had to invent their own terminal interface soft- ware will have a deep appreciation for this capability. Similar subroutines are provided for reading characters from the terminal or keypad, printing one or a string of ASCII characters, or writing digits in the LED display. To round out the terminal interface, software is provided in ROM to read and punch paper tape if your terminal is so equipped. Again, care has been taken to provide checksums on the punched tape which is automatically verified when the data is reloaded. This kind of attention to detail reflects the high caliber of the MOS Technology offering. One reason for this is the fact that MOS Technology sells a size- able portion of the KIM units to industrial users. This policy of building to industrial rather than consumer standards is also evident in the quality of the PC board, the 10 PC artwork, and the fact that the board is coated with a solder mask, a plastic coating which protects the printed wiring. To further emphasize their faith in KIM, MOS Technology gives you a 90 day warranty on the entire KIM system, not just the com- ponents. Mail-in repair service is available even after the warranty expires. Interval Timer Another feature of KIM which is finding its way into more and more microprocessors is the inclusion of a program controlled interval timer. The KIM board actually contains two programmable timers, but one is dedicated to control the keypad and cassette interface. Any count from 1 to 256 can be loaded into the timer by writing to the timer’s memory location. The user can control the scale of the timer by pro- gramming it to count every clock pulse or to count every 8th, 64th, or 256th clock pulse. This prescaling of the counter is done by decoding the last two address bits for the timer. Thus, the time scale is controlled by which memory location is loaded with the count. You might consider using a similar scheme whenever you have to write more than cight bits to control an external device: Just use the least significant address bits as data. When the timer has counted down to zero, a software interrupt is generated, noti- fying the program that “time has run out.” As soon as the interrupt is issued, the timer continues to count past zero (into negative numbers) at the clock rate. If the program is servicing other interrupts, it can read the counter register to determine how long ago (in machine cycles) the timer interrupt occurred. Memory Expansion If you are interested in expanding the KIM memory beyond the 1 K provided, you'll be glad to know that all the decoding for the first 4 K is provided right on the KIM board. All you need to provide is 4 K more of RAM chips and some buffers. There are two connectors on the KIM board; one called the expansion connector is for adding memory and bus oriented devices. The second connector, called the application connector, interfaces directly to the outside world. The expansion connector has all the address, data, and memory control signals. The application connector terminates the lines for the audio cassette, the terminal send and receive signals, and the 15 10 lines. Connections are also provided so that the keypad can be removed from the KIM board and mounted elsewhere, a useful feature if A COMPLETE MICROCOMPUTER ONLY $245 @ NOT AKIT! @ FULLY ASSEMBLED e FULLY TESTED e@ FULLY WARRANTED OPERATES WITH e KEYBOARD & DISPLAY @ AUDIO CASSETTE e TTY KIM-1 INCLUDES e HARDWARE KIM-1 MODULE WITH 6502 pP ARRAY 6530 ARRAY (2) 1K BYTE RAM 15 1/0 PINS e@ SOFTWARE MONITOR PROGRAMS (STORED IN 2048 ROM BYTES) e FULL DOCUMENTATION KIM-1 USER MANU SYSTEM SCHEMATIC 6500 HARDWARE MANUAL 6500 PROGRAMMING MANUAL 6500 PROGRAMMER’S REFERENCE CARD | 4) J [2 WS MBB Use THIS FORM TO ORDER YOUR KIM-1 TODAY! hea to: MOS TECHNOLOGY. INC. “” KIM-1, 950 Rittenhouse Rd.“ | | Norristown, PA 19401 city__ State. W Please ship me. KIN-1 Systems at a cost of $245.00 per system plus $4.50 for | shipping, handling and insurance (U.S. and Canada only) PA residents add 6% sales tax. (international sales subject to U.S. Commodity Control! Regulations. Add $20.00 per system for shipping and handling of international ordets.) My check or money order is enclosed for $, i Photo 3: Wiring for Staind Alone Use. With due re- spect to the instructions in the KIM-1 user’s manual, and addition of some mis- cellaneous parts, the re- sults will be @ wiring har- ness similar to that shown here. Wires have been attached and labelled for GND, +5 volts and +12 V. The audio cassette inter- face has been brought out to an RCA-style phono Jack assembly purchased at a retail electronics store, along with interconnection cables for the recorder in- put and output. This setup enables the user to enter and test out programs through the KIM-1 control panel and LED display. you want to wrap up the KIM printed circuit board in sheet metal along with a power supply. Documentation The documentation which comes with KIM is thorough and comprehensive. Any regular reader of BYTE should have no trouble following the details of the 200 page programming manual. There are plenty of examples; and the explanation of the opera- tions which occur in each machine cycle of multicycle instructions, while not essential, is very instructive. Special sections of the manual are devoted to interrupt handling and use of the stack pointer. This is vital information often glossed over in other manuals. 1 have to admit that | have not yet digested all the information in the 150 page hardware manual which came with my KIM, since my main interest is in programming my system as soon as possible. However, the manual scems to have a solid emphasis on 1O interfacing and usage of the control lines. The third manual provided is the actual KIM user’s manual. This 100 page document explains how the keypad, cassette interface and terminal interface are to be used. It gives 12 a few basic programming examples, includ- ing an example which goes through the entire design of a simple application using the 10 lines. My only complaint is that no sample program was provided for the use of the programmable timer or the ROM exccu- tive subroutines. Also, the listing of KIM should have been supplied as a standard item. Also included in the package is a pocket reference card for the instruction sct and a wall size schematic of the entire KIM board. Two other useful documents are available from MOS Technology on request. One is the manual for the 6500 cross-assembler, which is available on several commercial time-sharing systems. The other is the well- commented listing of the executive programs stored in ROM as mentioned carlier. In summary, the KIM is an excellent microcomputer requiring no assembly and which is very attractively priced. The only auxiliary equipment required is a power supply and a cassette recorder. The manuals are among the best available and the built-in keypad and display make KIM easy to get started with. The terminal interface and ease of memory expansion make it easy to upgrade as your requirements increase. Make a date with KIM — you'll enjoy it! = IF YOU'RE NOT DESIGNING WITH ACSC PROTO-BOARD; LOOK AT ALLYOU'RE MISSING. Uttlity— Models are available with or without built-in regulated power supplies (fixed or adjustable). Economy—Eliminate heat and mechanical damage to expensive parts. Save money by re-using ‘components. Versatility —Use with virtually all types of parts, including resistors, capacitets transistors, DIP's, 5's, LED's, transformers, relays, pots, etc. Most plug in directly, in seconds. Durability—All Proto-Board models are carefully constructed Of premium materials, designed and tested for long, trouble-free service. Expandability—Proto-Board units can be instantly inter- connected for greater capacity. Visibility—All parts are instantly and easily visible, for quick circuit analysis and diagramming. ‘Speed—Assemble, test and modify circuits as fast as youcan push in or pull out a lead. hours on every project. Adaptability—Use in design, piney — ae Sea packaaln with most types of clruits, inmany, many applications. Flexibility ‘or in conjunction with other accessories, such as scopes, counters, CSC Proto-Clip™ Use independently, Accessibility—All parts are instantly and easily accessible, for quick signal tracing, circuit me ic \odifications, etc. Varloty—A wide variety of models are available with gapacities ranging from 830 to 3060 solderiess tie-points (6 to. 32 14-pin DIP) fo fit every technical budget requirement. Whatever type of electronic circuits you work with, you can do more in less time with CSC's solderless Proto- Board systems. As fast and easy as pushing in or pulling out alead, you can design, test and modify circuits at will. Com- ponents plug into rugged 5-point terminals, and jumpers, where needed, are lengths of #22 AWG solid wire. In the same time you took to read this ad, you could be well on your way to assembling a new circuit. For more information, see your CSC dealer, or write for our catalog and distributor list. CSC PROTO-BOARD SOLDERLESS BREADBOARDS connectors, Design Mate™ test equipment, etc. One Proto-Board unit can serve a thousand applications. CONTINENTAL SPECIALTIES EASY DOES IT 44 Kendall Street, Box 1942 New Haven, CT 06509 » 203-624-3103 TWX: 710-465-1227 West Coast office: Box 7809, San Francisco, CA 94119 © 415-421-8872 TWX: 910-372-7992 Canada: Len Finkler Ltd., Ontario © 1976Continental Specialties Corp. Prices and specifications subject 1o change without notice. MoneL SOLDERLESS IC CAPACITY. MANUFACTURER'S OTHER NUMBER TIE-POINTS _(14PIN DIP’S) SUGG LIST IRES P86 630 6 81595 7 Tena PB100 760 10 19.95 it —with larger capacity PB-101 940 10 29.95 8 distribution buses, higher capacity PB102 1240 2 39.95 Large capacity, moderate price P8103 2260 4 59.95 Even larger capacity: only 2.76 per tie-point PB-104 3080 32 79.95 Largest capacity; lowest price per tie-point PB-203 2250 24 75.00 Built-in 1%-regulated BY, 1Alowriple pover supply PB-203A 2250 24 120.00 ‘As above plus separate Ye-amp ++15V and —18V internally adjustable regulated power supplies 13 Letters Establishing BYTE Com- mittees of Correspondence To encourage corre- spondence among readers, beginning with letters re- ceived after May 1 1976, BYTE will print the name and full address of each published letter’s author. if you do not wish your address to be printed, mark it “do not print my full address” or the logical equivalent. ON THE TRUTH AND BEAUTY OF BLINKING LIGHTS (AND OTHER SUBJECTS) The ‘Total Kitchen Information System” was a big hit since I’m constantly pestered by people who want to know what | could possibly do with a computer in my abode. Well done! | am glad to see that BYTE is attempting to reverse that great movement to rid com- puters of blinking lights. A computer isn’t a computer without blinking lights! Just com- pare an IBM 370/158 to a 370/155 (which it replaced) to see what | mean. Or how about the six foot light panel of a 360/195? Lights Forever! There scems to be a good deal of interest in the game of Space War. | wrote a version of Space War for an Adage AGT-40 graphics system a couple of years ago that was pretty successful. Based on my experiences, | could not guarantec that the game will be suitable for running on current micros since the computation overhead is fairly high. How- ever, some BYTE readers should be able to make simplifications to the game which will permit some level of it to be played. Kevin Kelley Wappingers Falls NY ON CODE TRANSLATIONS AND VACUUMS In your editorial in December 1975 BYTE you expounded on the need for a common high level language to facilitate the exchange of software between different computer systems. Another approach to the problem might be to write some sort of translation or cross-assembler routine to convert, say, 8080 into the equivalent, say, 6800 instructions. Such a scheme would use less memory than a high level language compiler and therefore be of more use to users with small systems (or budgets). I’m not sure how valid the scheme is and thought that perhaps you or BYTE’s readers could determine its validity. 14 | would also Jike to join Mr Ryland’s lament on the software vacuum. Another gripe along these lines is the “literature vacuum.” The manufacturers supply basic information on their micro- processor and that’s about it. Take, for example, the 8008. It was around for years with only Intel’s information until Martin Research came out with Microcomputer Design, a virtual encyclopedia on the 8008. It's a fantastic book, and | can’t seem to find such an “encyclopedia” for any other micro- processor. This makes it tough to compare microprocessors without buying a system based on that microprocessor, which gets expensive. Anyway, BYTE’s pretty good so far - keep up the good work. Brian Greiner Deep River, Ontario Where architectures are similar, trans- lation between instruction sets is quite feasible. Whenever ussembly code tukes advantage of ‘special characteristics” with no direct equivalent in the target machine of the translation, the result of a simple trans- lator will be what could at best be termed “inefficient” code. A complicated translator which takes advantage of speciul cases would tend to eat up a lot of memory for its program, just as a compiler or high level language does, One of the slowest methods of all would be to implement an interpretive simulation program on the target machine, which can execute the instructions of the source machine program. Such simulations are typically 20 to 50 times slower than real time execution on the source machine. These comments are obviously not the last word on the subject. A QUERY ABOUT THE AUDIO STANDARD | read with interest BYTE’s proposed cassette standard. I’m in agreement with all the specifications but one: the choice of mark and space frequencies. | think the mark frequency should be lower than the space frequency. It is desirable to be able to read into the computer two or more blocks of data as one “file.” For instance: To assemble a program on a tape that was produced by dumping several TVT pages to do this without error requires that the entire interblock gap appear to the computer as “mark.” To do this without wasting tape requires that the drive be stopped in the interblock gap. As the standard is proposed, special cir- cuitry is required to “edit” the Lape stop- page. If the mark and space frequencies are The Enlightened Altair Your Altair already has the allows scrolling at about 4 lines per intelligence, so let our VDM-1 Display _ second, eliminating complicated timing Module make the best of its capacity program routines. At top speed, the to communicate. This is not alimited display scrolls through a dump of 65K “TV Typewriter” The VDM-1 is an of memory in two minutes; that’s about ultra-high speed output device, built 1000 lines per minute! right into your 8800 system. Multiple programmable cursor The VDM-1 generates sixteen circuitry is built in. All 1024 cursors 64-character lines in a large easy-to-read can be displayed at one time or begin font with both upper and lower case anywhere in the display. Thus, the letters. It contains 1K (1024) bytes of | VDM-1 can display white-on-black or random access memory, to which the _ black-on-white—perfect for many processor can read or write, just as video games! The VDM-1 also features though the memory were an integral EIA Video output for any standard part of the system. As the information video monitor, or a television repair is written in, contents of the on-card shop can easily modify your own TV set. memory are displayed instantly without The VDM-1 comes with free interrupting the operation of the terminal mode software, designed for processor. teletype replacement when used with Once the processor provides the display status parameters, the VDM-1 can be made to “scroll” " - its display upwards or downwards. A built-in ila BASIC or our own Resident Assembly system. (Powerful text editing soft- ware and various game pack- ages are also available “<__ from Processor Technology Corp.) Our detailed VDM-1 Owner's Manual is available for $4.00, refundable with purchase of the VDM-1. Kit Prices, $179, premium grade, low profile IC sockets included. = Write Us, for details on our other compatible 8800 plug-in modules. Tech 6200-Y Hollis Street Emeryville, CA 94608 The important point is the need for proper operating procedure to prevent the “gap trash” from produc- ing errors. exchanged, and no writing is done while the tape is not at speed, no added circuitry is needed. Michael W Fellinger Boulder CO Harold Mauch, one of the participants at the standards conference, replies: Mr, Fellinger raises several interesting points which were considered by the partici- pants in the BYTE symposium. | think significance depends on the manner in which the cassette standard is implemented and used. | believe Mr Fellinger is assuming the interblock gap produces the same kind of deciphered output as the “marking” tone produces, This is not necessarily the case. First of all the interblock gap created by stopping and starting the cassette is full of trash caused by de-energizing and re- energizing the record head while the tape is decelerating and accelerating. This is heard ‘on playback as a “chirp.” Even if the mark and space frequencies were interchanged, the problem remains since the lower marking frequency will ‘“‘chirp’’ to the space fre- quency and momentarily be interpreted as a space, Second, there is a precedent in data communication for interpreting the absence of signal as a space. This is the idea behind a “break.” It is useful because it notifies the user or equipment of a signal or line fault. The 'teleprinter runs “open” or the “break” indicator comes on. Strictly speaking, either of the two fre- quencies could have been chosen as the “marking” state and would have made very little difference if the states were deciphered with a phase locked loop or other FM type discriminator. The type of cassette player with which this standard will be used “rolls off” or attenuates the higher frequencies. Consequently the higher frequency tone will be somewhat lower amplitude during play- back than the lower frequency tone. Since the signal level is most conveniently adjusted during the “marking” interval preceding a block of data, it is desirable that the marking tone be the lowest amplitude of the two tones. This would be the high frequency in most cassette players. The lower frequency tone would then always have a somewhat greater amplitude than the reference adjust- ment level increasing the immunity to signal dropout. Choosing the higher frequency as the “marking” state also permits circuit econ- omies if the deciphering is done digitally. A recorded character is ‘‘framed’’ by a leading “space” bit and trailing “mark” bits. The beginning of a character is denoted by the mark-to-space transition at the beginning 16 of the start bit. Obviously it is desirable to identify this event as precisely as possible. In the circuit described in the March issue of BYTE (and subsequent revision in the April issue and previously by Don Lancaster in BYTE No. 1) the existence of the lower frequency is indicated by the full cycling of a retriggerable monostable. The fact that it is allowed to time out indicates the presence of the lower frequency immediately and unam- biguously. Consequently the high-to-low fre- quency transition produces a_ relatively precise event. On the other hand the low-to- high frequency produces a condition some- what like saying “if you don’t hear from me {’m not going.” This leaves open the time interval in which to make a decision. Speci- fying that interval and acting on it involves a slight circuit complication which is not necessary with the proposal as stated. All of the above comments aside, the important point is the need for proper operating procedure to prevent the “gap trash” from producing errors. When opera- ting manually do not permit the computer to utilize the cassette output until well into the five second “marking” leader preceding each block of data. Identify the end of each block with a special character. For example: a line feed or ETX code if the content of the block is text or an asterisk (*) if the content is a program. This tells the computer to inhibit further response to the cassette. When operating automatically (computer controlling the tape unit remote control input) have the contro! program wait for a second or two of “clean” marking interval before accepting data from the cassette. If the ‘“‘no signal” condition produced the same output as the “marking” state, this pro- cedure could not be implemented as simply and effectively as it is. Harold A Mauch Dallas TX PAYING OHMAGE TO RESISTANCE The article on standard abbreviations, ‘‘K or k?” in the January 1976 BYTE by Manfred Peshka was interesting, but | noticed one major flaw in the abbreviation used for the unit of resistance, the ohm. Using the letter O is a very bad idea as, when it follows a number, it is difficult to identify the number and the units. For example, the article on blinking lights on page 53 had the following line: “The 222 O resistors...” I first thought this to be a typographical error until | read the standards article. It is always a bad idea to use O for anything when using the number 0 at the same time Continued on page 80 .get it ALL together! Please Contact One Of Our Distributors— Computer Way—Huntington Beach, California Bargain Electronics—LaMeda, California Comput-O-Mat Systems—Rye, New York The Computer Workshop, Inc.-Montgomery County, Wi CORPORATION OOO ee, RW Maryland Computer Mart Corporated—Boston, Massachusetts 940 North 400 East The Computer Mart of New York—New York City, North Salt Lake,Utah 84054 New York , Comunicaciones S.A.—San Jose, Costa Rica (801) 292-8466 Computer Country—Denver, Colorado DELIVERY: 60-90 DAYS a RD Boudinot PhD Computer Sciences Corp 6565 Arlington Blvd Falls Church VA 22046 For integrated circuits, physical and electrical equivalents sometimes have identical designations — and sometimes have completely different numbers. n Source The practice of one company supplying an assembly or a component which is equiva- lent to a product of another company is called second sourcing. In fact, there are often many alternatives to the original supplier; thus the title of this article. We shall discuss the history of second sourcing, why second sourcing has flourished, what the buyer’s risks are, and how to approach the decision process within the second source environment with specific application to personal microcomputer systems. The Price Umbrella The financial basis for second sourcing is the nature of the marketing strategies that have been historically applied to computer systems. Pricing has been a game of bal- ancing the capability of a product against its manufacturing cost. The strategy has been to produce a series of systems where each system is more capable than the one below. The low end machine usually sells at a small profit. By designing each system for eventual upgrade, it is possible to double the power of the entry level machine with a dispro- portionate hardware cost. For example, twice the capability may be expected to cost the user slightly less than twice as much. If the increased capability is achicved by simply changing a CPU clock, the profit potential is obvious. The difference between a Burroughs 2500 and 3500 is an example of a board-change upgrade. Figure 1 depicts a predicted end user price versus capability using an arbitrary 1.8 factor. In this figure, 16 times the capability costs 10.49 as much to the user. It seems like a bargain, but manufacturing 16 times the power may have only cost twice as 18 much. At this point, the vendor would be yielding 500 percent profit on the upper end machine and only a narrow margin on the lower end machine. The stage is set for second sourcing by companies who offer “twice the capabilities at half the price.” It must be noted that many other factors, costs, and risks, affect a manufacturer’s pricing. His real decision is a function of market research of how many machines he might expect to sell, how much it will cost to design, fabricate, and market them, how many will be upgraded initially or later, etc. All costs for machine design are spread over some number of machines (usually the num- ber of high probability projected sales) along with fabrication costs and markup. Then the final prices are established. If sales are as good as or better than predicted, fat profits may result. However, a large risk is always present, as the demise of the computer production divisions of GE and RCA has shown. History of Second Sourcing Second sourcing has been with the elec- tronics industry for a long time. It has long been expected that several manufacturers would make a 10 uF, 16 V tubular capaci- tor or a 1000 O, 0.25 W resistor. The same applies to tubes and transistors. One may purchase a 6BE6 manufactured by GE, RCA, or Sylvania, among others. Likewise a 2N2222 may be purchased from Motorola, RCA or Texas Instruments. Finally, among discrete components, electrical equivalency is often cross-referenced between a given manufacturer's line of transistors and other transistors not manufactured by him. A common tactic is to make a general purpose Figure 1: End user cost versus capability. End user cost is shown on horizontal axis for increasing capability on the vertical axis. In the example, increasing the cost by an arbitrary factor of 1.8 doubles capability. 18 324 5.83 1049 device which meets or exceeds the require- ments of a large number of devices. The Radio Shack fine of 37 transistors which cross reference to 20,000 other designations is an example. The first lesson many people learn about second sources in discrete com- ponents is that electrical equivalence does not guarantee physical equivalence. Attempting to fit an equivalent part with a TO-3 case into a circuit board where a failed TO-92 case was originally used teaches a lesson which is rarely forgotten. The advent of the integrated circuit brought greater attention to second sourc- ing. The 9000 series and 7400 series pio- neered by Texas Instruments and Fairchild were quickly copied, once success was evi- dent, by numerous competitors. ICs, like discretes, became fair game; confusing equiv- alent numbers were eliminated and everyone now numbers a 7410 as a 7410. The $1998 clock chip manufactured by American Microsystems, Inc (AMI) is an electrical and physical equivalent of the MM5316 made by National Semiconductor Corporation. However, the 1103A made by AMI is an equivalent of the Intel 1103A 1 Kb RAM. In LSI (large scale integration) second sources sometimes are numbered the same as their equivalent, and sometimes not. Large Computer Second Sourcing The potential profitability of second sourcing was described above. Such profits can be realized only in a successful market. Just as IBM became the giant controlling more large computer sales than all its com- petitors, likewise, it became the obvious and somewhat vulnerable target for second sourcing. Although large computers and systems existed for a decade, it was not until the late 1960s that viable second source alternatives were developed and marketed with significant success. IBM received substantial competition from vendors offering: (1) peripherals, such as disk drives and controllers and remote terminal controllers, (2) core memory, and (3) terminals. Several law suits followed, the most famous of which was Telex versus 1BM and 1BM’s subsequent countersuit. Telex accused IBM of monopolizing, and IBM accused Telex of stealing proprietary infor- mation. The efforts to divert IBM business con- tinue from a variety of sources. In all areas of peripherals, core, and terminals, alterna- tives to IBM equipment exist; in some cases there are many choices. As with com- ponents, alternate devices sometimes bear designations which disclose relationships and sometimes they do not. For example, an Itel 7330 disk system replaces an IBM 3330 disk system, On the other hand, an alternative to an IBM 3270 CRT is the ADDS 980A CRT. Minicomputer Second Sourcing Second sourcing in the minicomputer environment has been aimed primarily at peripherals and core. Sophisticated terminal subsystems are not generally used with minicomputers and certainly not in the quantity to make the area as lucrative as it is in the large scale computer environment. Among peripherals, alternate sources are often derived simply by modification of an interface. If a peripheral maker who supplies brand X designs a tape reader and punch or line printer whose interface is easily modi- fied, then supporting brand Y with the same 19 Second sourcing is univer- sal for discrete com- ponents — generally any 100 O resistor will do, and in many circumstances any 0.01 uF capacitor will suf- fice in an appropriate application. Isolating the real problem in the midst of five dif- ferent vendors claiming their hardware meets their specs (yet the “system” won’t run), could exceed anyone’s patience. Increased production with a minimum of additional overhead means more competitive prices and re- duced costs. device requires only a small capital invest- ment. Increased production with a minimum of additional overhead means more com- petitive prices and reduced manufacturing costs. The second source alternatives in mini- computer core memory developed as a result of two factors. First, the pricing strategies applied to large scale computers were also applied to minicomputers. Therefore, each successful minicomputer created a second source market. Prime examples are the Data General Nova 800 or 1200 and the Digital Equipment Corporation (DEC) PDP-8 or PDP-11. Other less widely sold systems (in terms of total sales) such as the Hewlett Packard HP-21XX series, have also been the object of second sourcing when a large amount of expensive, additional core is added to a computer for the resultant increase in productivity. This type of machine generally supports multiple users in a timesharing mode, where the number of users efficiently handled is a function of the amount of core memory available. Second, advances in solid state memory provided alternatives to traditional core memory. Benefits included cost and speed, although these parameters gradually improved from marginally to substantially in favor of solid state memory. Microcomputer Second Sourcing The second source market in micro- computers is directed at memory and 10 boards. From all indications, terminals may soon be included in this market. Currently, the peripherals market is limited because tapes, disks, readers, and punches cost more than microcomputers. The only inexpensive devices for external storage now available are the audio cassette type. The peripherals market can be expected to expand rapidly, as will the alternate sources. Microprocessor users will continue to appreciate the signifi- cance of the chip name: Microprocessor. Computers are “processors,” which require inputs and produce outputs. Inputs are primarily originated from terminals or pe- ripherals and outputs must be passed to terminals or peripherals. A microprocessor alone has few uses. 20 manufacturing For two reasons, main memory is cur- rently the major second source item in the microprocessor area. First, if RAM is pur- chased from the supplier of the micro- computer kit, 8 KB of memory costs more than the basic kit in almost every case. Second, after terminals, main memory is second in importance to an operative sys- tem. The memory available limits the size of programs and data buffers and determincs the level at which programming must be accomplished, i.e., machine language, assem- bler, interpreter, or compiler. 10 control boards represent a unique area of second sourcing. Almost no such parallel exists in large scale computers. Some special purpose boards are available for mini- computers, but they are mostly limited to special AD, DA, or multiplexer interfaces rather than conventional IO interfaces. Risks to the Second Source User We have discussed the wide variety of second sources available, ranging from dis- crete components to peripherals, micro- processors, and IO boards. The risks and problems are just as divergent. Discrete components such as resistors and capacitors are intrinsically low in risk. They either work or they do not. Their per- formance parameters are readily measured and little confusion is possible. Likewise, more complex components such as tubes and transistors are easily checked for almost all parameters in conventional testers. More complex devices such as TTL and CMOS chips are fairly easily tested in terms of switching function, voltages, and loads only at low speeds. Failures at circuit speeds are not easily detected on a unit basis. However, suspected devices are relatively easy to replace, and they seldom fail. Computer peripherals represent the potential for enormous problems. Some clas- sic fingerpointing contests have centered around systems consisting of an [BM main- frame with brand A tapes, brand B disks, brand C core, and brand D terminals. Iso- lating the real problem in the midst of five different vendors claiming their hardware meets their specs (yet the “system” won’t run), could exceed anyone's patience. » Core memory followed a slightly dif- ferent pattern and the risks have changed. Initially, some mainframe vendors dis- claimed any warranties and refused to pro- vide maintenance service if another vendor’s core memory was utilized. The courts did not concur, and mainframe vendors were forced to allow second source memory to be integrated with their systems. One problem was thus relieved, but the fingerpointing possibility still exists. Additional micro- processor systems’ considerations will be discussed in the next section. 10 and other special purpose boards are susceptible to the considerations discussed above. Additional considerations relevant to their selection are discussed in the next section. It is clear that some of the problems in using second sources in large scale or mini- computer systems do not equally apply to microprocessor systems. Larger systems are generally maintained by their vendor(s). Microprocessor systems tend to be main- tained by their builder/integrator. How to Approach the Decision Process The following discussion will address microprocessor systems only. The five con- siderations in second source selection are: Support Cost Performance Physical characteristics Electrical requirements. Each will be discussed separately in terms of its relationships to the decision process. A methodology for deriving a selection that leaves the weighting factors up to the indi- vidual will be presented. The support area includes: @ Initial documentation © Services available from the factory or regional offices, such as consultation when a problem arises @ Other integral hardware and software. Documentation includes not only adequate construction instructions but also debug instructions for use if the unit is inoperative after construction is complete or if it fails later. Detailed instructions regarding the use of all switches, in the case of the main- frames, and software tips, in the case of peripherals, are also important. Determining the adequacy of support is the most difficult of all the evaluations to be made. One rule of thumb is to rely on more than one source of information if at all possible and never to use second hand information. The product cost is the easiest to deter- mine. For investments of significant size, a phone call to check the latest price is often very profitable. Unlike most market areas, microprocessor and related components are continually decreasing in cost. The Novem- ber issue of BYTE lists the cost of a4 KB memory board for the ALTAIR 8800 at $264. A conversation with an ALTAIR representative in early November 1975 placed the price under $200. Performance characteristics may not be readily available. When buying a stereo amplifier, one of the parameters always compared is RMS power in watts. In the microprocessor environment, all timing data is not always published with the advertise- ment. RAM memory varies almost on order of magnitude in speed. Among the 2102 RAM series alone a 6:1 relationship exists. The speeds of 2102 devices are listed in table qa Physical characteristics include height, width, depth, and weight. If a board won’t physically fit in an enclosure, electrical compatibility has little meaning (unless you are prepared to rewire by hand). Also to be double checked are plug and socket com- patibility and heat dissipation. Electrical characteristics are very impor- tant considerations. The primary parameters are current requirements and the impacts on the bus. Each microprocessor kit that includes a power supply in the cabinet has an inherent limiting factor. Arbitrarily, we will assume that a 10 A, 5 V supply is Table 1: 2102 RAM access speeds. Device Designation Access Time 2102 2102-1 2102-2 2102-8 2102-4 2102-A-2 2102-A-4 1000 ys 500 ps 650 us 1500 us 350 us 250 us 450 us 21 Microcomputers are truly an idea whose time has come, Table 2: Expandability example. Components System A Components System B Basic System 2a Basic System 2A Two 10 Boards 2A Two 10 Boards 2A 12 Memory Boards 6A 6 Memory Boards 6A Total Required 10A Total Required 10A System A expandable to 48 KB ‘System B expandable to 24 KB memory memory included. If the “bare-bones” processor microprocessor system that does not have a requires 2 A, and each 10 board requires 1 A, and two IO ports are required, then the current load before adding core memory is 4 A. This leaves 6 A available. Now we have a decision point based on present and future memory and IO requirements. If the vendor 4 KB memory board costs $200, and the second source board cost $100, the choice may seem obvious. It is often the case that vendor boards require low current. We’ll use 0.5 A as an example. The second source example will be 1 A. If no future require- ments for special interfaces are planned, then the decision is a straight forward evaluation of core memory expandability. The expandability problem just described is depicted in table 2. Given the same basic system, configuration A, using vendor sup- plied boards, is expandable to 48 KB of memory. Configuration B is only expandable to 24 KB memory using the available power sup- ply. The decision is further clouded if two more IO boards are contemplated for the future, resulting in the new limitations of table 3. The decision then is based on whether 16 KB of core, the limitation of configuration D, is sufficient for project requirements. The second main electrical characteristic to consider is the number of TTL loads an alternate board will drive. In a bus system allowing expansion up to 20 boards, each board should be able to drive 20 loads. Otherwise, a limitation to expand- ability is introduced. Software characteristics include the avail- ability of vendor or second source software. If a high level language is required, any Table 3: Expandability example. Components System C Components System Basic System 2a Basic System 2A 4.10 Boards 4A 410 Boards 4A 8 Memory Boards 4A 4 Memory Boards 4a Total Required 10A Total Required 10A self-hosted, high level language available at an appropriate cost is unacceptable. Soft- ware considerations are also appropriate for special interfaces and devices. If supporting software is not available, it sometimes proves to be a long tedious job to develop sophisti- cated handlers. Finally, firmware (software stored in read only memory (ROM)) may be a major consideration. Firmware monitors and assemblers are available for M6800 systems via the vendors and for 8080 sys- tems through alternate sources. Dis- advantages of firmware vary slightly de- pending on whether ROM or erasable pro- grammable read only memory (EROM) is utilized. If a ROM is “burned in,” no options exist for easily modifying or patching the firmware. Such a requirement results when a bug, or program error, is detected or when new applications or hard- ware make modifications desirable. It is hoped that the latter case is more common. One approach worth considering for a sys- tem that is expected to grow in the future is to use a firmware monitor and bootstrap loader to load all operational programs, compilers, and interpreters from an external storage device, such as a cassette. There are certainly cases, however, where a firmware assembler or BASIC interpreter is the best choice. A Decision Matrix Example A final example, to be used only as an example, is included. Because each selection must be made on an individual basis, the actual companies and parametric data are not included in the example. System C expandable to 32 KB memory System D expandable to 16 KB memory 22 The first step is to establish a method of ranking each contender in each area: sup- port, performance, physical characteristics, electrical requirements, cost, and software. Within each category, the criteria of excel- lence must be established by using discrete measures where possible. If the scales to be used will range from 1 to 10, then the criteria for achieving each ranking must be established. Then the relative weightings for each characteristic, perhaps 50 percent cost, 40 percent electrical, and 10 percent soft- ware, must be established. Finally, mini- mally acceptable standards must be deter- mined for each category. It is possible for an item to rank worse than the lowest incre- ment by being a physical impossibility. In table 4, items flagged with an “x” are unacceptable. Thus we see that brand B does not meet the minimum electrical specifica- tion, brand C exceeds the cost range, brand D will not fit physically into the cabinet, and brand E was unacceptably slow. Fur- ther, in this example, support, physical characteristics, and electrical characteristics have a weighting factor of 0.0. They were factors for elimination but not comparison. The decision was binary: Acceptable or unacceptable. This decision matrix technique is of considerable value, even if one has no confidence in the weighting factors, because it forces a systematic comparison and evalu- ation of all characteristics of the choices. It has been used by the author on numerous occasions and has dispelled numerous mis- conceptions. The hard facts lined up against each other can be most revealing. Conclusions In conclusion, there are three key points to be made. (1) Second sourcing is a healthy GLOSSARY Capability: In a broad sense, the capability of a system is a weighted sum of the individual features which make a system easy to use and reliable. In a more specific sense, a particu- lar capability of a system is a point of com- parison with equivalent points on other sys- tems. (A general capability might be the ability of a system to accomplish a particular application; a specific capability might be the mass storage medium employed in a system.) Firmware: In the context of this article, firmware means software which has been written into a read only memory. A second definition of firmware applicable to microprogrammed machines is the set ‘of microprograms required to emulate a specific CPU architecture. Table 4: Sample decision matrix. X designates unacceptable. Weighting scale of 1 to 10; 10 is best. 8 € 2 2)_ 8 2 =8/3 2 2 z| = |ggles & 2 a fp |e 2 2 $e / 5 |Z2/25) 3/6 | 8 |ss a a jeojwe|/S | 3/4 |28 Brand A 2/2 ;/3 1/2 )/84 ]9]5 Brand B x Brand C x Brand D x Brand E x Brand X 2/5 |4 {3 | 2 |4 | 20] 64 Weighting Factor o } 04/0 | 0 | 05} 04 phenomenon. In fact, because second sources establish product credibility and guarantee users that someone will be able to supply them, many chip makers actually seek a second source. (2) The benefits to the source user are primarily monetary; how- ever, there are hazards, and they must be considered before making a decision. (3) Finally, it took the large scale computer market a decade and the minicomputer market several years to develop second source markets. Using the date of intro- duction of the ALTAIR 8800 in January 1975 as the date of initial general avail- ability, the microcomputer industry has achieved this maturity within its first year of existence. Microcomputers are truly an idea whose time has come.@ Microprocessor: This means any of the large scale integration (LS1) computer designs currently avail- able and used for inexpensive personal computing systems, Second sourcing: The practice of “follow the leader as applied to the electronics and computer technology. One company designs and markets a product; then a second (or third, etc.) company takes the external functional specifications and creates an equivalent circuit which will accomplish the same functions. The second sourcing is often sanctioned by licensing arrangements. The second source company for any given product is always in a following mode, since the product's innovator is by definition the first firm in the marketplace. Vendor: The commercial term for the source of a product is “vendor.” 23 The important advantages of a ROM in microcom- puter use are nonvolatility and write protection for whatever data it holds. A bootstrap or absolute loader is a simple program which just transfers data from an input device to memory. To keep it in your machine, it should ideally be in ROM. System monitors are prime targets for ROM technology. Read Only Memories in Microcomputer Memory Address Space Dale Eichbauer Digitech PO Box 6838 Grosse Pointe Ml 48236 In an earlier BYTE (see “Read Only Memory Technology,” page 64, December 1975), Don Lancaster introduced the use of read only memories as a tool for design at the hardware level. This application is but one of a multitude of uses for ROMs, especially when you consider a ROM as part of the main memory address space for your computer. The important advantages of a ROM in microcomputer use are nonvolatil- ity and write protection for whatever data it holds. It relieves the user from the chore of reentering frequently used programs each time his machine is fired up or after data is accidentally modified. To put it simply, your data is a/ways in the machine whenever you need it. The two most common and well known uses of ROMs are for holding loaders and system programs. There are two basic types of loaders: the bootstrap (or absolute) and the more complex relocating loaders. The bootstrap or absolute loader is a short program which is used to load the machine following a power interruption or any other type of catastrophic failure which wipes out the main programmable memory. (Unless your machine’s programmable memory is of a special design, it is volatile, meaning that its data is lost if power to the memory is fost for more than a very short time.) This loader program requests input from a peripheral device such as a paper tape reader or cassette drive which contains pro- grams needed for machine operation and stores this input data in programmable memory. After toggling all your data in from the front panel following power interrup- tion, one can easily see both the convenience and versatility of such a bootstrap loader. 24 The relocating loader takes the input data from the peripheral device, converts its addresses from a relocatable form into absolute binary and stores it in memory at selected addresses. It might typically per- form some error checking and turn over execution to the loaded object program. Monitors and Debuggers System programs suitable for or, prefer- ably, in ROM include such things as system monitors, assemblers, device drivers, soft- ware debugging programs, hardware fault testing and diagnostics. The system monitor (which is often available from the computer or CPU manufacturer) is a program which handles and coordinates machine operations at a basic level. A monitor allows the user to control the entire system’s operation with simple, powerful commands. A typical moni- tor might have commands for the creation, modification, and deletion of files, device independent 10 (from the user’s point of view), automatic assembly and execution of programs, relocation of programs and data, and so forth. Device drivers (short programs which handle the software end of peripheral interfacing) are rarely changed once debugged and are needed for almost all 1O operations, making them a natural for ROM storage. Software debugging programs, often manufacturer supplied, provide a means of detecting and correcting programming faults. The many forms and features which they possess are too extensive for any detail in this article. One rather unusual but poten- tially useful application of ROM storage is in storing hardware testing and diagnostic routines. Testing of the microcomputer often can be done by simple programs which execute an algorithm and compare the re- sults with the correct answer. !t can also be done by complex programs which execute all functions of the machine, often in cer- tain critical combinations peculiar to the machine under test. At first it would seem that there is no need to put these routines in memory of any type until needed except for convenience, since it would be an infre- quently used task. Consider, however, the case where a fault which is to be located is in some way related to or impeding the input or the programmable memory’s storage func- tions. If this is the case, then the testing or diagnostic routine may never get into the machine in usable form to do its job. Simulation and Emulation Simulation is another use of ROMs in microcomputers which will become more common as CPU capabilities increase, ma- chines proliferate, and users demand more of their machines. Simulation is the technique of interpretively executing an instruction set for one computer design using a program running on a second “host” machine. For example, a host machine with an 8080 CPU could execute object programs from another machine which uses a 6800 or PACE CPU (or even 1BM 360/370 software for those with delusions of grandeur). A ROM could con- tain the simulator program to execute the foreign instruction set. With an appropriate general purpose simulator program it might even be possible to change the instruction set of a machine by referencing a different ROM data table for each simulated machine. Of course afl such simulations run much more slowly than the actual speed of the computer in question. A related technique is emulation, in which microprogrammed hardware imple- ments an instruction set directly. Some microprocessors are internally micropro- grammed, but the user typically will not see this fact externally. Microprogrammed com- puters are fairly widespread in contemporary technology. And with nearly every micro- programmed computer, there is a control store implemented in some form of ROM. But the majority of microprocessor chips currently available do not give the user a facility to use microprogramming tech- niques. The instruction set is typically com- mitted by the manufacturer during the design stage; so, to perform the software of a foreign machine, a software simulator must be used as described above. With such simulations, the slowness of operation is due to the fact that a series of instructions (a subroutine) must be executed on the host computer in order to achieve the effect of a single instruction of the simulated machine. Even though a simulated computer may be 10 to 50 times slower than the real machine, such slowness is often tolerable when compared to the time it would take to hand translate the program. Use of ROM to store the simulator makes the simulation mode virtually a part of your hardware, protected from destruction due to power loss or accidental modification during pro- gram execution. Subroutines Another excellent use of ROMs is the storage of subroutines. Multiply, divide, double precision, floating point, conversion formulas and other algorithms, plus addi- tional software implemented functions are in the machine as soon as power is applied. When they have been implemented in ROM, such subroutines act as if they were really hardware instructions. Security Data Anyone assembling a multi user computer system, especially one with remote access, should consider using a ROM for main- taining data pertinent to the various users of the system. This data might include such things as access codes, what devices and memory segments are authorized for use by which individuals, the particular user’s sys- tem priorities (for job and device scheduling by the operating system), and so forth. The Operating system constantly needs such in- formation to make decisions concerning the handling of tasks for the current users. A ROM protects this information from modi- fication or destruction, whether accidental or malicious. Tables An excellent use for ROMs is the storage of tables of values. There are many tables, such as logarithmic, sine, cosine, and tangent values, which could be of use to almost any computer hobbyist. A program needing one of these values then has to merely look up the desired value in the appropriate ROM table. Such tables can also be used to speed up high precision calculations by giving an approximate starting value. Those faced with interfacing a non-ASCII encoded terminal or other peripheral (such as EBCDIC, Selectric, Baudot, or Hollerith) to their microcom- puter may find that a character conversion table, implemented in ROM, is part of the solution, as Don Lancaster points out in BYTE #4. However, while his conversion scheme uses a ROM which does its conver- sion of data apparently at the peripheral itself, in many cases it would be useful or desirable to perform this conversion in the machine. Such a conversion method would even make it possible for two terminals, whatever their coding scheme, to commu- 25 If you plan to do a lot of simulation, the simulator program might be a logical choice for ROM. With dili- gent software preparation, your humble 8008 could simulate a mighty 360/370 (although much much more slowly in execution). A library of often used subroutines is another item which would make a good candidate for ROM storage. Data tables for character code conversion via soft- ware can be stored in ROM if they are used a lot. If you want to use your computer as a low fre- quency (audio) waveform generator, you could burn a set of standard waveform patterns into ROMs, using software to drive a DA conversion device at vari- ous frequencies. nicate with each other using the microcom- puter (and its ROM) as a sophisticated interpreter. And, if data rates, character lengths, and line lengths are different, then such a setup offers the added advantage of using software and memory as a buffer to compensate for these differences. Waveforms If your machine is equipped with a DA converter (digital to analog converter), then a ROM can contain a set of values which, when output through the DA, will produce a custom waveform. In many cases special waveforms may be generated in this fashion which would be impractical to generate, using any other method. Both the frequency and amplitude of the waveform may be controlled completely by software. With an 8 bit word and a DA with 10 volts full scale output, resolution of 0.04 volts per bit is obtainable. The maximum generated fre- quency is dependent on the speed of the microcomputer and the number of outputs per cycle required for a suitable waveshape. Error Checking and Arithmetic Two other possible uses for ROMs which may be implemented either in main memory or as processor add-ons are a parity gener- ator/checker and a fast multiplier/divider. A table for all possible combinations of a word can be referenced to generate the parity bit or a flag check bit. Multiplication and division may also be done as table functions. Several of the IC fast multipliers currently available are actually modified and specially programmed ROMs, The article in BYTE #4 also introduced Programmable Read Only Memories (PROMs), which are the most useful type of ROM for computer hobbyists, since a cus- tom pattern costs very little to have pro- grammed or the user can do.it himself.@ Bibliography on ROMs and PROMs These articles are found in engineering publica- tions, which should be available in well stocked corporate or university libraries. “PROMpting a minicomputer” by Robert High- tower of Motorola in the February, 1973, Electronic Engineer/Systems Engineering Today. This is a description of a bootstrap (or absolute) and a relocating ioader for a PDP-11 which is stored in ROM, “PROMs, Proms, Promises” by Jerry Metzger in June 16, 1975, Electronics Products Magazine. This is a good introductory article on PROMs and includes a wall chart of all PROMs available, both bipolar and MOS, as of its publication. “PROMs — a practical alternative to random logic"’ by Dave Uimari of Signetics in the January 21, 1974, Electronic Products Magazine. Here is an excellent article on PROM theory and use which also includes lengthy discussions on programming, such as how it is done, best place to have it done, typical large and small scale equipment, etc.; lists PROM programming services and equipment manufacturers. “Designer's Guide to Semiconductor Memories — Part 1" by Robert J Frankenberg of Hewlett- Packard Data Systems in August 5, 1975, EDN magazine. This is a good introduction to all types of memories, ROMs and PROMSs included; it also includes an excellent list of references. “Read-Only-Memories in computers — where are they headed?" by Roger R Dussine of Com- pagnie Honeywell Bull and Robert M Zieve of Honeywell Information Systems in the August 1, 1972, EDN magazine. The authors provide an overall survey of ROMs, their use in computers, mentions use for fault location, bootstrap, some unusual types of ROMs, and things to come in ROM technology. “Programmable ROMs offer a digital approach to waveform synthesis by Karl Huehne of Motorola in the August 1, 1972, EDN magazine. This is a detailed description of ROM waveform synthesis. “Large Bipolar ROMs and p/ROMs Revolu- tionize Logic and System Design” by Joe Mc- 26 Dowell of Monolithic Memories, Inc in the June, 1974, Computer Design. Here you'll find a short survey of the current bipolar ROM technology and some examples of use, including a ROM controlled timing pulse generator under microcomputer command. “Mixing Memories in Minicomputer-based Con- trol Systems" by Richard A Farwell of Data General in the February, 1973, Contro/ Engineer- ing. This is @ discussion of how various memories are used in Data General minicomputers and the costs and tradeoffs involved; a section on ROMs lists a number of uses outlined in this article. Manufacturer's data sheets on particular devices contain a wealth of information and are free for the asking. As an example, the data sheets below contain listings of ROM and PROM lookup tables of values. From AMI: © A 256 word sine and cosine table in the $8614 supplemental note. © An arctan table in the $8771 supplemental note. © A 512 word sine and cosine table in the $8772 data sheet. © A Hollerith to USASCII conversion table in the S8457 data sheet. @ A USASCII to Hollerith conversion table in the $8539 data sheet. From Nitron: © A Hollerith to ASCII conversion table in the NCM 1112 data sheet. © A Selectric to ASCII to Selectric conversion table in the NCM 1151 data sheet. © A 512 word sine and cosine table in the NCM 1141 data sheet. From Computer Microtechnology: * ASCII to EBCDIC and EBCDIC to ASCII conversion tables in the CM 2850 sup- plemental note. Can anyone beat the Altair System? We doubt it. When it comes to microcomputers, Altair from MITS is the leader in the field, The Altair 8800 is now backed by a complete selection of plug-in compatible boards. Included are a variety of the most advanced memory and interface boards, PROM board, vector interrupt, real time clock, and prototype board. Altair 8800 peripherals include a revolutionary, low-cost floppy disk system, Teletype.™ line printer, and soon-to-be-announced CRT terminal. Software for the Altair 8800 includes an assembler, text editor, moni- tor debug, BASIC, Extended BASIC, and a Disk Operating System. And this software is not just icing on the cake —it has received industry wide acclaim for its efficiency and revolutionary features. But MITS hasn’t stopped with the Altair 8800. There is also the Altair 680—complete with memory and selectable interface —built around the new 6800 microprocessor chip. And soon-to-be-announced are the Altair 8800a and the Altair 8800b. OS cues MITS doesn’t stop with just supplying hardware and software, either. Every Altair owner is automatically a member of the Altair Users Group through which he has access to the substantial Altair software library. Every Altair owner is informed of up-to-date developments via a free subscription to Computer Notes. Every Altair owner is assured that he is dealing with a company that stands firmly behind its products. After all. we didn’t become the leader by messing around. Shouldn't you send for more information or visit one of our Altair dealers? Please send me the following information: CO Your latest catalog and price list CO Software information package O Please include a list of your dealers 7 1 1 1 1 1 1 t 1 NAME. H 1 t 1 t 1 J ADDRESS. 3 STATE & ZIP. pce verre led 2450 Alamo S.E. Albuquerque, N.M. 87106 More Information on PROMs Roger L Smith 4502 E Nancy Ln Phoenix AZ 85040 Have you ever wanted to program your own read only memories automatically so that you could copy programs into a per- manent storage device? This article concerns one kind of erasable read only memory, the Intel 1702A integrated circuit and its pin compatible equivalents the National MM5202AQ_ and MM5203Q. These memories store 256 eight bit bytes of data using a method which allows total erasure and reprogramming many times. The method of programming is complex while erasure can be accomplished simply by exposure to an ionizing radiation (such as ultraviolet light). When you need to store large tables of data or programs, use of such read only memories is a very attractive alternative to more elaborate types of memory provided a method of programming is available. These erasable read only memories are economical as well, since typical prices at the time of this article are in the $20 range. Why PROMs? A few years ago, it became apparent that the different users of read only memories (ROMs) had many special applications which required only one or two copies of any given data pattern. The technology of mask pro- grammed read only memories is only cost effective for large production runs of parts so an alternative had to be found. A means was needed for the user of read only memories to inexpensively field program one or two copies of a data pattern. This is where Harris Semiconductor, a division of Harris Intertype Co., entered the picture and coined the term PROM for programmable read only memory, a Harris trademark that has become almost generic through wide- spread use. A PROM then was simply a ROM that could be programmed in the field. 28 While production read only memories are manufactured from specific masks provided weeks in advance by the user, a PROM can be programmed in seconds automatically by the user reducing turn-around time to a minimum. Types of PROMs Let’s examine some of the different PROMs in use today. There are a number of options for the memory elements used in making programmable read only memories including nichrome fuse links, diode matrices, stored charge devices, amorphous semiconductors, polycrystalline silicon fuses, etc. Note that all these memory elements can be electrically altered in order to store data. A few can also be restored to the original condition; these are used in erasable read only memories (EROMs). Figure 1 illustrates how the basic PROM operates. The first thing to notice is a decode circuit. This decodes the address to select one of the 32, 64 (or whatever) word gates in the memory matrix. The decoder is simply an array of multiple input gates with one input for each address bit and one gate for each memory word. Each decoder gate drives a multiple emitter word driver transistor. In series with each emitter is a memory element which in this case is a fusible link. In this example, we have a 4 bit word so each word driver transistor contains 4 emitters, each con- nected to a fusible memory element. The memory elements then connect to the appropriate bit sensors and output buffers (4 in this example). When a particular word is addressed, its decoder and word driver transistor turn on. If the fuse link is intact, the bit sensor turns on and the output line for that bit goes low (logical zero). If the fuse link is open, the DECODE ADDRESS LINES: nERERE Figure 1: This partial schematic of a PROM shows the WORD PROGRAM DRIVER CIRCUIT TRANSISTOR MEMORY ELEMENT Ht Hl G2 @—— ou TPuT BIT To OTHER q aITs SENSE AMP FROM OTHER D /ORDS. 2 PROM would be the nichrome fuse link type. sensor and buffer circuit remains off and the output is high (1 bit). Not shown in the diagram are the chip select (or chip enable) lines. The chip select lines are typically connected to the higher order address bits. When many PROMs are utilized, an external decoder circuit (such as 74154 or 7442) might be used to decode several high order address bits and decide which PROMs to enable or select. Essen- tially, the chip select inputs are used to turn on the output bit sensors and buffers when the PROM is selected. PROMs use open collector or tri-state output buffers so that they can be bused. The buffers are in the high impedance state until enabled. The nichrome fusible link type of pro- grammable read only memory is manufac- tured by Harris, Signetics, Texas Instru- ments, and Motorola. From this basic nichrome fuse PROM, other types have evolved. The next natural step was to poly- crystalline silicon fuses, as made by Intel and Advanced Micro Devices. These are easier to build in the semiconductor fabrication proc- ess because the fuse links are also made out of a semiconductor material. The silicon fuses are burned open in the same manner as the nichrome fusible link type. Due to the semiconductor structure of the memory elements, these PROMs often require a more elaborate programmer than the nichrome fuse type. Another development in memory ele- ments is the Avalanche Induced Migration (AIM) device patented by Intersil. Fabrica- tion of these elements is similar to TTL logic which simplifies the manufacturing process. The elements are basically NPN transistors arranged in a matrix with common collectors on the X-lines and common emitters on the Y-lines. In programming a logical one, a high current is forced through the desired transis- tor from emitter to collector. The emitter to base junction is forced beyond normal avalanche and into secondary breakdown. Aluminum flows into the junction causing a base to emitter short that in effect leaves a base to collector diode. These PROMs are programmed using 2.5 us pulses of 200 mA current that are alternated with sense pulses. After a number of pulses, a change is sensed and the programmer moves on to the next bit. Erasable ROMs A memory element used by Intel and National Semiconductor is a stored charge type called a FAMOS transistor. FAMOS stands for floating-gate avalanche-injection MOS charge-storage device. It is similar to a P-channel silicon gate field-effect transistor with no contact on the gate. Programming the FAMOS type of memory element re- quires a pulse more negative than —30 volts applied to the drain or source P-N junction. High energy electrons are injected into the floating silicon gate. With this negative charge on the gate, there is current con- duction between the source and drain of the FAMOS transistor. The primary advantage of this stored charge type of memory element is that the charge can be removed later by exposing