On: Cpm65: CP/M for the 6502

[EvanAnderson]

This is an interesting rabbit hole. I'd never really looked into the 65CE02[0]. I guess I always just assumed it was a die shrink of the 65C02. I didn't realize that the chip had really interesting new features. It's a really cool evolution of the 6502.

[0] https://en.wikipedia.org/wiki/CSG_65CE02

[JPLeRouzic → EvanAnderson]

Why not using Hitachi's 6309?

https://en.wikipedia.org/wiki/Hitachi_6309

It has two 8-bit accumulators, A and B, and they can be treated as a single 16-bit accumulator, D.

It has two 8-bit accumulators: 'E' and 'F'. These can be concatenated to form 16-bit accumulator 'W'.

The D accumulator can be concatenated with W to form 32-bit accumulator 'Q'!

Two 16-bit index registers X and Y

Two 16-bit stack pointer U and S

Transfer register 'V' to speed up inter-register instructions.

A 8-bit register, DP, to set the base address of the direct page.

8/16-bit Zero register '0' to speed up operations using a zero constant. This register always reads zero and writes to it are ignored.

[johnklos → JPLeRouzic]

I don't think a 6309 would work on a Commodore A2232.

[JPLeRouzic → johnklos]

Replacing a 6502 by a 6809 (or a 6309) is difficult but it can be done, for example:

https://anachrocomputer.github.io/sixadapt.htm