<Assuming that this is electrically the same as the S100 version, then...
<
<The 8097 is the data buffer betwen the RAM and the S100 DI lines. It's
<used on reading only. I don't see how it would affect writing to the RAM
If the input is internally shorted to either rail. I've seen this mode
of failure on old chips.
<There are some 74LS08 AND gates that are used as buffers between the S100
<DO lines and the RAM inputs. It's possible that one of these has become
<faulty, I think.
Entirely possible.
<There is a 74LS175 latch (well, actually a pair of them) between the RAM
<outputs and the character generator. Now one bit of that chip could well
<be faulty (IC6 on the S100 card, I think).
Yes, also possible.
<Not so. One of the most common failure modes of old IC's is that the
<bondout wire between a pin and the silicon die breaks or comes adrift. If
<the A2 line (pin 12) of the character generator had failed in this way -
<or if the input buffer in the ROM had failed - we'd see exactly this
<pattern.
Also true but less likely.
Allison
Received on Thu Mar 05 1998 - 22:40:37 GMT