VT101 8085 CPU Fault
mouse at Rodents-Montreal.ORG
Sun Jan 18 19:28:58 CST 2015
>> Perhaps this really is an indication that the ROM is bad, if it is getting $
> No. That should not be possible.
> The RD line comes from the CPU and is used to fetch data. The CPU
> should continue to fetch data unless it has halted.
I'm probably just exposing my ignorance of the 8085 here, but did it
have anything like the prefix opcodes x86 has (repne et al)? I'm
wondering if it could be stuck doing something like (to admittedly try
to use syntax I don't really know) "repne cmp %ax,%ax" that would never
occur normally but might compute forever without fetching anything
further. Or, does it have a instruction prefetch buffer? (My guess
would be it's too old for that, but I don't really know.) If so, a
very tight loop might execute entirely out of the prefetch buffer....
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