Hi folks, On Sep 7, 2022, at 1:33 PM, Michal Pleban <lists_at_michau.name> wrote: > tokafondo_at_tokafondo.name wrote on 05.09.2022 00:55: >> It wouldn't be a 6502 anymore but it could behave as it if wanted. I go back to the x86 comparison. The i80486 can run i8086 code. > > If you want this new CPU to have more opcodes, you need to repurpose some illegal 6502 opcodes for the new operations. So it will not behave exactly like a 6502 anymore. Technically correct, but incompletely so. I have personally encountered at least five mutually incompatible processor families descended from the 6502. All of them are immediately recognizeable _as_ 6502s, despite some of them having been assigned very different names. Moreover, while they generally can't handle code meant for their "cousin" processors, every single one of them can still run programs written for the _documented_ behaviour of the original design from all the way back at its release, when it was still being manufactured in PMOS. So, fundamentally, "6602-compatible" is either a very /imprecise/ description with more than a dozen possible interpretations, or a description with a chokingly narrow definition that is nigh-impossible to extend. Pick your poison. :¬) (My own solution was to dream up something _inspired by_ the 6502 design rather than _building on_ it, but as I doubt I will ever get around to actually implementing my version, I'm not going to pretend my opinion on the matter should carry all that much weight.) Sincerely, Gordon S.Received on 2022-09-08 00:00:03
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