Light Pen for the SVC.
I have wanted one of these for quite some time, and eventually saw an rule describing one in
the Maplin magazine. The article describes a design for which a kit is available from Maplin,
naturally. Although the unit is not supposed to be for use with
I thought it just might
work, and the price was fay reasonable.
It’s an easy kit to build, with only a single IC used to shape the pulse from the light
sensitive transistor. Unfortunately, at present all I get on it is random numbers. I suspect the
pen circuit is producing a negative pulse, and the documentation for the SVC doesn’t say what kind
of pulse it is expecting. Positive, probably.
The other possibility that occurred to me was that perhaps the pen was picking up too much
stray light, or was not properly shielded from the electrical noise Marvin puts out. I would be
interested to hear from anyone with experience of using a light pen with the SVC, and will naturally
pass on anything that works properly!
Ben Martin wrote to me, expanding on his suggestions for an amateur priced extension board for
80-BUS systems, among other things. (The other things included a suggestion that I should stop
moaning my boring job, and something positive to get out of the rut. He bas a point, but I
enjoy a good moan, and can’t promise not to do more of it, even if I escape the rut.)
He has obviously put quite a lot of thought into ways of making elderly Nascoms and 80-BUS
machines in general able to use IBM type disks (wll, can’t the MFB series do this already? It must
be possible.) [Ed. – systems running Gemini BIO.S 32 or later can read/write IBM PC-DOS disks with
the IBM-COPY program, available separately.] and made some interesting suggestions about how we
could use their software by emulating the hardware. It wouldn’t go fast enough. But never mind.
Marvin has mow reached a stage of expansion where there are only three slots left on the mother
board, and I am not sure I want to add more processing power to the brute. For a start, there are
already two boards contending for a set of port addresses – the modem and the Belectra board. The
bus is heavily used already, with the
and SVC in situ.
I have considered various processors as possible candidates for an expansion board, ranging
from exotic bit slice things from Texas, to the 32032 from National Semiconductor. The latter is
too complex. The obvious choice of processor, if one wants real power, is the Transputer, or
rather, lots of them. At the moment, they cost a lot. But nothing falls like the price of chips,
and some time soon, they should reach a sensible level. I have been looking at OU courses which
teach Occam, so I will be ready to program them. But rather than hang them onto Marvin, and make
him eves more complex, I have to decide to halt extensions to the system. Not that I am going to get
rid of Marvin; too many useful functions to list are now second nature on this machine. But I am
getting a new machine. It will be used in conjunction with Marvin, once I work out an interface.
And it will not be an IBM type machine. After all these years of criticising machines with plastic
cases, and making snide remarks WIMPs, I am going to have both.
The machine in question is expandable, although not as easily as an 80-BUS computer is, and it
is multi-tasking, and it am ideal candidate for use with Transputers, as a ‘front end’. I’m getting
an Amiga A500. And before you say it isn’t IBM compatible, and is therefore a side-track in
evolution, I should point out that British Aerospace are using A1000s as workstations because they
are so much better than IBMs. Somebody demonstrated one to me, and I was hooked. The mouse is
good, graphics arc (gulp) better than the Pluta. It has a poor BASIC, but Modula 2 is
easily available, and worth having.
I hope that I will become good enough with the machine to write about it, but will probably
send any stuff I produce about it to Amiga based magazines. I feel it would be out of place here,
apart from details of how I connect the two machines, perhaps, if I manage to do it.
It is going to feel very strange, after all these years, having a machine the same as other
people’s. It will be a luxury, too, being able to buy programs instead of having to write them
myself. But give up the Nascom? Never!