by Richard Bateman
The I/O Systems Graphics Board.
The I/O Systems Graphics Board appears to be a very attractive product –
giving very high resolution at a reasonable price (384 dots by 224 dots by 55.00). It
uses bit mapping and uses 10.5K of your memory when all the screen is displayed. The
board does not contain any video memory itself, but is connected to a 16K block of the
RAM (A) or (B) board.
What do you get ?
An assembled PCB 4.25″ x 3.75″, double sided but not plated through, with 6
socketed ICs, 3 resistors and 6 100n capacitors. There is also a 33 way low quality
edge connector and a 35 page very high quality manual. Unfortunately there are no
circuit diagrams and no real explanation of how it works.
This is the hard part. You have to lift several ICs on your precious Nascom
and RAM board and make connections – 35 in all – with not very good instructions. It
is quite difficult to know where to mount the board as it does not conveniently fit
anywhere. Overall the board is not the easiest thing to connect or mount, but with
some imagination it can be done.
Does it work ?
Very well, an extremely stable video with good clean lines. The result is
better than with the original video as no accesses are made to write to the screen
during the display refresh time. In fact the Z80 is shut down during the display
refresh, which can be nearly 75% of the time, so don’t expect fast displays with this
system as it is equivalent to running with a 1MHz clock (compared with an N2 at 4MHz).
The I/O Graphics Board is a clever implementation of a simple idea, possibly a
little overpriced when the penalties are considered. The detractions are, considerable
loss of system RAM, reduced operational speed of the system, and difficulty in
performing a workmanlike job in connecting the card. I liked the manuals (with regard
to programming the card) and the superb graphics that may be implemented. Overall,
good, but really only applicable to dedicated graphics freaks.
The graphics card costs 55.00 and is available from:
I/O Systems Ltd.,
__, _______ ___,
London, ___ ___.
Philips mini-digital cassette recorder. Brand new, in original wrapping with
interface diagram and information. Superceded by disk system before interface was
purchased from Currah. Cost 109.00. Will accept 95.00. __-___-____
Siemans 40 track, single sided, double density 5.25″ drive. Owner upgrading to
double sided so 110.00. __-___-____