It was a 4 MHz Z-80 based single board
computer with 256 bytes each of RAM and ROM, and also serial and parallel
interfaces, all on a
“Eurocard” board
10×16 cm in size:
The CPU and ROM are missing on this board. The parallel port was a Z80 PIO, a chip I came
to hate. I seem to remember something about no status registers. If an interrupt came and
you didn't handle it immediately, there was no way to know that it had ever happened.
This board shows a number of hacks I made. The transistor next to the 8251 was, I think, to
convert from RS-232 to the 20 mA current loop
that Tandem terminals used. The
DIN connector was to connect a tape cassette recorder, which I still have and may photograph
some time.
All in all, for the day it was a surprisingly compact system. But the problems outweighed
the advantages. The ROM monitor was so buggy that it was just about useless. I patched it,
but there's not much you can do in 256 bytes without the ability to re-assemble the code.
And clearly it needed more memory. The backplane had provision for 5 cards, so that was
possible, and I designed and built both RAM and ROM boards with wire-wrap technology:
I suspect that the sockets are for 2702 PROMs, 512 bytes each.
I didn't use this machine much: it was far too limited, and the proprietary bus meant that I
couldn't buy extension boards except from Kontron. In contrast to the kit, the other boards
were very expensive. On the other hand, in the USA they were building relatively cheap
systems based on the S-100
not-quite-standard, so the next
machine was S-100 based.
