> On 2022-09-05, at 16:51, Jim Brain <brain_at_jbrain.com> wrote: > >>> But would that also cover the illegal Opcodes correctly? From what I understand, those are side effects of the NMOS implementation. >> >> Were they? I always considered them to be a side-effect of the internal decoder matrix which did not specifically "NOP" the unused opcodes (which IIRC was done with the CMOS versions), but just bluntly decoded the individual parts of the opcode, generating corresponding enable signals. >> >> So stuff happened like e.g. loading the accumulator, but also throwing the X register onto the internal data bus. > > As I recall, a few incomplete decodes enabled two things to bump data onto a bus, which would then boil down to NMOS behavior with 2 outputs pushing electrons to the input. Still, you don't always have to go bottom-up and reimplement NMOS physics to get the desired behaviour. Top-down approach is OK sometimes too. You know.. if it looks like a duck, walks like a duck and quacks like a duck.. ;-)Received on 2022-09-06 15:00:03
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