Yours to Command
Britain’s own microcomputer – The Nascom 1
K.S.
Borland
(From Personal Computer World – Volume 1, Issue 1 – 1978)
|
Yours to Command 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 complete 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:-
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.
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 linkedto 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 thesystem. 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 in 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 shapesand forms. The games industry,
specially in America,is getting ever more ambitious. From simpler
gameslike Life and Hangman, to games of Startrek andSpace War. The even
more ambitious will attemptChess. Of course, the more complex the games
thelarger the RAM necessary. So Lynx will be lookingforward 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 offers5K. This should suffice to accept more
advanced programs. The third
option is the most difficult. What is goingto 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 780 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. Allthe 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. Inkit
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.