16 Nov
2000
16 Nov
'00
12:37 p.m.
I haven't
played with mine in a while, but was reminded
of this by a comment in a current ebay auction. Whenever
I put a Cromemco 16FDC or 64FDC in an IMSAI box, the front
panel stops working (the 4FDC doesn't do this). Looking
at the schematics for the Cromemco boards, I can't see any
reason for this, but watching the behavior of the FP lights,
it looks like the board is driving the data bus whenever a
wait is asserted. Can somebody else with the 16FDC or 64FDC
schematics take a look?
It was how they implemented the RDOS shadow ROM. There was a
Cromemco tech-note that came with the 16FDC that showed some
mod to allow it to work with the IMSAI front panel. IIRC, the
result was you had to key in something like three bytes of code
to get it to boot automatically from the floppy.