BigDumbDinosaur wrote:
Some of those undefined opcodes that map to NOPs are multibyte instructions. If KB-9 used any of them there's no telling what might happen.
BDD's right. And we have three processors at issue here: the NMOS, the Rockwell cmos and the WDC cmos. If there's an undefined opcode encountered I think it must have been put there intentionally -- it had a function (intended to execute on the NMOS part). Both of the cmos versions will fail to perform that function. And it's plausible that the failures would differ from one another -- one conspicuous, the other subtle. Perhaps we need to question more closely the observation that the Rockwell cmos runs KB9 properly.
Commie wrote:
my tests are conclusive
Not yet. IMO it won't be conclusive until you find out what happened, down to the exact instruction.
It's apparent that the WDC chip is somehow different, but not all differences are defects. I think we'll find that the WDC parts live up to their published specifications,
if we get to the bottom of the matter. The question is how to do that
-- Jeff
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