Re: Modern, but fully compatible 6502?

On Sun, 4 Sep 2022, Gerrit Heitsch 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.

Rainer