On: Cpm65: CP/M for the 6502

[johnklos]

Since CP/M is a primarily text-based OS, I wonder if I could port it to the 65CE02 in a Commodore A2232 serial card. It only has 16K of RAM, but the RAM is fully accessible by the m68k in the host system, so it should be easy to load the OS and give it access to a virtual disk.

I feel a project coming on...

[EvanAnderson → johnklos]

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