Electronics > Projects, Designs, and Technical Stuff
Science of Cambridge (Sinclair) MK14 restoration
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glarsson:
If the trace was without PROM installed then the Z80 is reading the opcode FF, rst 38h, over and over again.
mpk:
Here are some more traces. The first two are CS on PROM (yellow) vs D0 (purple) and the same for a RAM chip. The third (just a bit of fun, don't cha know) is chip select on PROM (purple) vs RAM (yellow).
mpk:
(by the way - one interesting point is that I have no idea whatsoever if the PROM chips are the right way round as they were completely unmarked. I can easily work around that by swapping them over to check both combinations when debugging..)
glarsson:
You can't just turn chips around willy-nilly. The probability of a blown chip is high depending on where the power pins are located.
mpk:

--- Quote from: glarsson on October 25, 2018, 05:06:01 pm ---You can't just turn chips around willy-nilly. The probability of a blown chip is high depending on where the power pins are located.

--- End quote ---

Yes, I know that. What I mean is that there are two 4-bit PROMs - one has the high nibble of the monitor code, the other the low - and they may (or may not) be swapped over.
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