Doctor Dark’s Diary – Episode 18.
Horror story to make your flesh crawl!
My cat recently discovered that he could just fit into the spare space in my
system’s rack frame (shudder!) and he proceded to do just that. Some time
later, when I came to use the machine, I found huge masses of loose fur on the
rear of the end board, and thought that his usual static charge would almost
certainly have destroyed pretty nearly all the memory on the board, which just
happens to be my first MAP80 RAM board, with 256K of highly expensive chips on
it. So I cleaned the fur off, as carefully as I knew how, panicking all the
time, and cursing steadily in Finnish (the only language suitable for swearing
on such a scale – an example would surely destroy the disc it was saved on, so
I leave it to your imagination) and ran a test, which consisted of copying a
full disc to drive P, using the verify option of PIP.COM to test the memory.
This eventually came up with a verify error, and I thought my worst fears were
confirmed. But the amount of space left on P was 58K. So it looked as if the
MAP board was OK, and that the problem must be on the modified Gemini GM802
64K board also on the system. This board had been modified in accordance with
MAP80’s instructions, but because the virtual disc had never been full before,
the GM802 modification had never been fully tested.
To summarise, I have a Nascom 2, MAP80 RAM with 256K, modified Gemini GM802
with 64K, Gemini GM809 disc controller, and IO Research Pluto graphics board.
It seems very likely that there must be some sort of addressing conflict going
on between the Nascom 2 and the GM802, so that when a program attempts to read
the top 64K of memory, provided by the GM802, it manages instead to read the
Simon ROM, and the verification fails. If this is so, and I am only guessing,
how do I change things to cure it? Any suggestions from all the hardware whiz
kids among you would be most gratefully accepted. A letter about the problem,
which I sent to MAP80 a long time ago, has still not been answered, which
earns them a black mark.
A.S.A. Advertisement of the Year Award.
I should like to nominate Climax for this award, on account of their
misleading statement that there is no need to pay over two hundred pounds for
a colour graphics board. Their board costs £199, to which you have to add VAT
at the usual 15%. That comes to more than two hundred pounds when I work it
out... [Ed. – only if you are NOT a company AND live in the U.K.]
Colour Graphics – Why Pay More Than £100?
If you can only afford that much, and you want your 80-BUS system to have
colour graphics, here is one of my more intelligent hardware ideas. You can
have 256 x 192 colour graphics, in eight colours, although the display does
not fill your television screen, having a border all round it. The graphics
unit will be able to run programs independantly of the main computer, which is
obviously a good thing. All you have to do is buy a 16K Spectrum, and
interface the 80-BUS to its edge connector. All the data and address lines are
there, along with the Bus Request and Bus Acknowledge lines, so the Spectrum
could be treated as a page of memory by the 80-BUS system. All you have to do
is design a simple circuit to go between the two systems, and you will make