[Coco] "Reading" non-readable bytes with PEEK vs ZBUG

[Darren A.]

> In answer to your question, no. Look back up and see where the post byte is loaded in cycle #2. It also reads NNNN+2. By that chart the address buss at cycle 3 is still pointing to the address after the postbyte.


That looks like a typo to me. It shows NNNN+(2). The number in parenthesis is for when the opcode is preceded by $10 or $11. For cycle 3 it shows NNNN+2(3).


> At some point in the four cycles the address will have to be what is in the contents of the X register and not the PCR(NNNN+2).

Yes, that would be in cycle 4. When address $FFA0 is read, bits 6 and 7 are floating, so bits 6 and 7 on the data bus retain stale data from the read of NNNN+2 in cycle 3.

I won't argue anymore. It doesn't really matter what the mechanism is and the issue is of little importance (except maybe to Roger and his use of LOADM). The results seen in software correlate perfectly with my hypothesis. I may be wrong, but I'll stand by my findings until someone can show real evidence to refute them.

Darren

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