(This document saved from http://www.ps8computing.co.uk/nascom.htm and re-formatted by MIXTEL to reduce file size and increase compatibility with non-Microsoft browsers. Original ownership of this material by Personal Computer World is acknowledged.)

Britain’s own microcomputer – The Nascom 1

K.S. Borland

(From Personal Computer World – Volume 1, Issue 1 – 1978)
The electronic hobbyist in the UK has been left out in the cold. His spending
power is generally far less than that of his American counterpart. The fall-out
of products or peripherals from our highly specialized electronics industry is
minimal. It was in this climate that Lynx Electronics decided to go into the
micro business.

Lynx Electronics is the hobbyist subsidiary of North American Semiconductor, known in the UK as NASCO. John A. Marshall, Chairman of the North American Semiconductor group, is frequently in the USA; particularly at the NAS American headquarters in California. The west coast is a major area of electronics development and has a well-organised hobbyist industry. With members of the NAS operation he was able to visit amateur clubs and see at first hand the standard to which they have risen.

The American hobbyist scene has developed a long way. New technology, now predominantly MPU in fact, whole systems are available; and with these there is a wealth of peripherals. The clubs are not only well organised and well attended but have become forums where the small and medium, and even the large American electronics manufacturers, feel the need to be represented. Most colleges and universities that have an electronics department run a computer club. As nearly everyone who deals with either
hardware or software is a member of a club it is very important to the American electronics industry that products are made readily available and that new developments are rapidly broadcast. What do we have in the UK? We would suggest, virtually nothing. This is possibly unfair to those who are trying very hard to start, such as the Amateur Computer Club. But there are very few facilities available, and as the British electronics industry does not seem to have heard of amateurs, it must be hard going.

It was against this background that the NASCOM I evolved. The project has been to produce an advanced technology kit and put it within the U.K. mass purchasing market. The design had four major concepts. We set out to:

  • Firstly, produce a microprocessor system that is of intelligent use to the home user and in basic price around £200.
  • Secondly, use the best available mixture of products on
    the market, within our price range, and with it to produce the maximum possible system. There is, of course, an advantage here that an independent design has over a manufacturer limited by his own product range.
  • Thirdly, that whatever product was used the object must
    be to obtain the greatest possible control by software.
  • Fourthly, to design a system that would offer the user
    major future expansion. The design must be standard enough to offer a competent engineer the opportunity of adding his own expansion.

Also Lynx must be prepared to offer an expanding range so that the software enthusiast can expand his system.

If it was possible to produce a microcomputer like this and the British amateur was ready to buy, then it might be possible to start a national NASCOM club. As well as being ideal for the amateur it would solve many educational problems by creating a low cost microcomputer. This could open up computers in colleges all over Britain and the Continent.

This project started in the summer of ’77 and NASCO commissioned Shelton Instruments Ltd. in London to design the NASCOM I.

Shelton Instruments specialise in the design of control equipment using microprocessors. They are capable of design around most available processors. A feature of the NASCOM I design is the trade-off between the hardware and the software.

To the great belief of us all the project is a complete success and the NASCOM I became reality. The design team had a free choice of microprocessors and decided on the Mostek Z80. Apart from the help that was freely given by Mostek, the main reasons for choosing the Z80 were:-

  • It is a third generation, 8 bit, LSI, CPU chip.
  • It is designed to require the minimum of hardware interface. It has an easy to learn instruction set. This instruction set however is powerful enough to give flexible and efficient memory usage.
  • It is rapidly becoming a popular device both in the professional
    market and for the home computing enthusiast.
  • There is a fair amount of software already written for the Z80 for home applications.
  • The Z80 will execute all 8080 software.
  • There are multiple sources for the Z80 family.
  • It has a simple power supply requirement.

At the centre of all microprocessor systems is a Central Processing Unit (CPU). This manipulates data as directed by the instructions stored in the memory (program). It can be thought of as containing three sections:-

  • An arithmetic and logic unit (ALU) which processes data, eg adds two numbers together, combines two numbers on the basis of a logical AND and so on.
  • A number of registers which are simply single word stores, some of which
    operate as pairs giving 16 bit capability.
  • Control and timing circuits to synchronise the various minute steps that need to be taken to implement the program.

Information is transferred to and from the computer system via the input/output circuits. The CPU processes data as parallel rows of bits and in many cases the input/output data is transferred in that form. For an 8 bit system the input/output bus consists simply of eight parallel wires.

All systems use some form of clock as a basic timing reference for instruction executions, memory and input/output operations.

In order to form a system the CPU must be linked to the other component parts. In general the connections can be divided into three groups. The data bus, the address bus and a number of control lines. The address bus is used to select an address in memory or to select some other external location. The number of address bits is not directly related to the word length used in the processor. The actual number of bits does determine the number of different locations that can be addressed. Eight bits give 256 different addresses whereas 16 bits give 65536 addresses. The function of the control lines include data strobes, an address strobe, reset, interrupt and flag lines.

A microprocessor system is illustrated in Fig 2. The control system is present in the ROM (read only memory) and the program and data are stored in the RAM (random access memory).

And so to the NASCOM I. In simple terms it is a computer kit, created by a hobbyist company, for use by hobbyists. Instead of selling the home user new equipment the design started with what was available: a television and a cassette deck. Any computer system needs a VDU so the basic NASCOM I has an interface to a domestic TV through the aerial socket. Similarly an ordinary audio cassette is used for storing and loading programs and data on standard magnetic cassette tape.

The Z80 CPU is connected to the memory and the input/output areas through a three-bus system. There is a 1K x 8 EPROM which has been pre-programmed with a monitor program. It comes into operation immediately power is supplied to the system. This allows the user to utilise his kit when he has assembled it.

It has been obvious from the design stage, when considering expansion, that even a hex keyboard(0-9, A-F) would not suffice. So a full ‘QWERTY’ keyboard is supplied.

Data and programs are entered via the keyboard and the monitor program will interpret and execute the required operations. The user may enter his program into a RAM memory for future use under control of the monitor program.

The monitor has these main functions:

  • Enter information into the memory.
  • Tabulate the contents of the addressed memory on the television screen.
  • Store memory on cassette tape.
  • Load memory from cassette tape.
  • Start the program from any given memory address.
  • Stop program at a pre-determined
    point.

When the program is stopped at a breakpoint the monitor program automatically copies the internal CPU registers into the RAM. They can then be examined by displaying those particular RAM addresses on the television. When a user program is started the internal registers of the CPU are loaded from this area. This allows starting data to be pre-set by the programmes.

The basic NASCOM I has a 2K x 8 static RAM. All of this is available to the user. However, to run the television as a VDU it is necessary to use 1K as a character store. Bit serial data is passed to and from the cassette recorder via a serial interface. The keyboard is controlled by the monitor program. There are few I/O circuits in this system and therefore there is no need to have an address decoder. The individual port addresses are such that address bus bits can select the right peripheral. To keep the memory address decoding simple the memory is arranged in two rows of 1K x 8. This means that to address 1024 address locations needs 10 address bits which are common to both rows. To select the correct row the EPROM needs three morelines. These are obtained through suitable decoding circuits.

The basic NASCOM I is in HEXADECIMAL with the monitor program accepting the HEX codes. However, Lynx have been lucky enough to associate themselves with a software house, namely Starbase.
Many of the software orientated hobbyists are already using some form of high
level language. This posed the problem of what software to produce first. It was already decided to produce a BASIC tape, but many people want an assembler. However, the decision has been to produce a TINY BASIC for a 4K RAM. The first one hundred will be
supplied free to those who have bought an expansion board or enough RAM. They
will be asked to report on the acceptability and then it will be committed to ROM. After the BASIC is in operation an assembler will be investigated.

Various hobbyists have already intimated that they will be writing an assembler so it may be available fairly quickly through the NASCOM Club.

So what can the NASCOM I do for the personal user? What software back-up will be available? The questions are so open ended. For example, there will be about 45% of the hobbyists who are competent engineers, and another 45% will be programmers. They will have different problems. Those who are horrified at assembling the kit will be offered the NASCOM I made up. There will be an assembly surcharge and kits will be made against orders. For those who may have software problems, the solution is less obvious. As the project progresses the library of tapes will be ever-expanding, and as the computer is for the hobbyist there is no doubt that the range will be enormous. But the hobbyist will not necessarily want written programs but help with writing his own. Lynx do not propose to teach programming, but help could come from two quarters. Firstly, and officially, Starbase is there to help. That is their occupation. They will be happy to receive problem programs and suggest solutions. For this there will be a charge.

The other possibility is the NASCOM Club, of which more later. However, these problems themselves generate an interest to the hobbyist. As a starter, many engineers will be
learning programming and many programmers will start dabbling in hardware. Many are
competent in both fields,but a very large proportion of the letters received by Lynx after their Wembley seminar were from buyers or potential buyers whose immediate excitement was to expand into a new medium: one which is a unique combination of entertainment and usefulness.

There are so many ideas and areas to explore. Control in the home. Heating, cooking, security. Games, both adult and junior, come in many shapes and forms. The games industry, specially in America,is getting ever more ambitious. From simpler games like Life and Hangman, to games of Startrek and Space War. The even more ambitious will attempt Chess. Of course, the more complex the games the larger the RAM necessary. So Lynx will be looking forward to many complex game players. Not only are the games fun to play, they also give practical experience in writing programs. How about writing an electronic diary? A home computer could remind you, day-to-day. It could look after your finances. Remind you of payment days. There are great possibilities as a teaching aid.

The NASCOM I is capable of graphics. The only graphics produced so far are very simple, but with the time the hobbyist has, many complex graphics will soon appear. To aid with amateur radio. Photography offers many ideas, such as colour analysers and filter choice.

The initial NASCOM I has its command EPROM, and 2K of RAM. Of this 2K there is 1 K devoted to the TV display. This leaves about 1K free. As a starter this is quite sufficient. Writing programs in HEX will limit the complexity but allow the hobbyist to get into the Z80 user language. From then on user needs will be guided by applications. Lynx has foreseen the need for expansion and have already produced their starter accessories.

As the only possible expansion on the main board is a 1K EPROM, the first need is for an expansion board. There is no ideal board. Many specific boards generate problems of supply and this increases the cost. However, there must be choice. So the expansion board has been designed for choice. Even on a multi-option board there is argument as to its options. Lynx has designed its expansion board for three main options. The board itself will be through-plated and will include a decoder, an address multiplex logic and the CAS and RAS strobes. The first and most obvious option is to increase the RAM available to the user. So there is an option for 4K or 8K of dynamic RAM. This should be enough immediate expansion for most users. However, some may want to expand very fast into much higher capacity. Although RAM boards are not immediately available they are planned for early 1978 and will probably offer 16K per board. As the user advances to the stage of needing more options, many will have specialised their use into one main area. The monitor program will be in continual use and therefore it seems reasonable to commit it to a ROM. As a second option on the first expansion board Lynx have decided to offer up to 4K of EPROM. These are sold in 1K blocks and together with the 1K EPROM option on the main board offers 5K. This should suffice to accept more advanced programs. The third option is the most difficult. What is going to be linked to the NASCOM I? The system already offers a spare parallel I/O on the main board. But this will not suffice for very long so Lynx have added the option of another PIO kit to the expansion board.

Having reached this stage let us look at cost. As has already been intimated the NASCOM I micro-computer costs £197.50. Assuming that the user has a TV set then all that is needed to start is a power supply. Many hobbyists will have a power supply available but if this is committed then Lynx are able to supply one at a cost of £24.50. The other option is extra sockets for the TTL. The main components are socketed but many users will prefer to socket all the logic. This costs £4.90. This means that even with extras the hobbyist is offered a Z80 based micro-computer for the grand total of £226.90 (plus VAT). This is what Lynx set out to achieve. Although there are many methods of operation, choice of modem, format of display etc that will no doubt be discussed, and some criticism will be right. Lynx would ask everyone to consider if it would cost even fractionally more. There are obviously more possibilities available at £250.00 and even more at £300.

So we have a kit working out at £227. Let us now consider expansion. The obvious expansion is in RAM. The maximum at present is 8K of dynamic RAM. This will cost £97. So we now have a system with 9K of RAM at a cost of £324. Together with all the power and control already offered in the NASCOM I, with 9K of RAM it is unbeatable. With our 8K extra RAM it is likely that the program to control 8K of data is past the simple stage. The maximum EPROM available is 5K at a cost of £87.50.The system by now probably needs various extra peripherals. So let’s add a PIO kit at £11.50.

We now have an expanded system which includes a NASCOM I, 8K of dynamic RAM, 5K of EPROMand two PIO’s in addition to the TV and cassette player. At a total cost of £423 for a very powerful computer system. Lynx will have the capability of loading the PROMS as the users complete their programs. However, it is the aim of every hobbyist to be self sufficient. So Lynx offer an EPROM Programmer. This will program 2708 type EPROMS. The programmer will plug into the NASCOM I bus. All the timing, address generation and data handling is performed by the NASCOM I using a special program. The program voltage is generated on the card from a +12v supply. It uses TTL parts and the price includes a special zero insertion force socket. In kit form Lynx have managed to offer this at £55. To go with the programmer Lynx offer a kit to make up an EPROM Eraser at £32.50.

The whole project already offers more for less and it has only just started. We have discussed briefly the climate in which Lynx decided to produce the NASCOM I. What has been produced was based around a price and the chance of expansion. The NASCOM I will have an immediate effect in that, at the time of writing this article. Lynx have sold 400 kits in the two weeks since the launch. The media have shown great interest and, although Lynx would like universal approval, there will no doubt be varying comment once they have a chance to use a NASCOM I. Comment and information exchange is the other side of this project. It may be naive, impracticable or even arrogant to attempt to start another
computer club with no more facilities to offer and certainly less expertise than those already in existence. But we intend to try. This is not started without thought. There do seem to be certain advantages in this situation. Starting a club does of course revolve around the success of the NASCOM 1. But after the seminar, where 500 people gave it the
thumbs up, and as Lynx has received more than two thousand enquiries, it would seem to be well on its way. Further, Lynx has had hundreds of enquiries from educational establishments from sixth form colleges to universities. This area of sales has not even started yet although twenty or so colleges have ordered one or more computers. The NASCOM I is the ideal teaching machine as it incorporates the Z80.

But this is not the main interest as far as a club is concerned. The sale of the NASCOM I to the general public will, of course be national, and so will the sale to colleges. It would seem reasonable to suggest that most colleges would start clubs especially if a fair proportion of the members had their own compatible hardware. There are certainly clubs in some colleges already. Southampton and High Wycombe spring to mind. But as far as we know there is no connection between them. This is where we see the possibility of the NASCOM club. Each member will have access to the other members and, when and if they get started, each local club would have knowledge of the others throughout the country. Nothing new in any of this, but it is not being done at present, and in a country like the UK it is not only possible but quite practical. For all the enthusiasm that Lynx people have, this still is entirely in the hands of the UK hobbyist. By March 1978 hobbyists will have kits spread throughout the UK and could by the end of 1978 number in thousands.

Advertisements

0 Responses to “PCW Interview”



  1. Leave a Comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s




Advertisements