Re: R65C02 PI

[Michael Mahon <mahon@cup.hp.com>]

John Bowling wrote:
> 
> As to why I think there is a problem with using an R65C02:  if you are
> running some old software that makes use of non-documented opcode quirks
> in the 6502, such as a lot of copy protected software for the //, the
> Rockwell chip is more likely to do strange stuff to you than a WDC
> standard 65C02.  Sorry I didn't make that clear.  That's also why the GS
> (along with the programmers jumping into undocumented locations in
> ROM, DOS, or ProDOS) can't run much of the early software.
> 
> John
> 
> --
> --==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--
> - John Bowling          -- Shouldn't you be commuting by bicycle?
> - johnlb@primenet.com   -- No, that's not a valid excuse!
> --==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--==--

I was never a big game fan, so there may be a lot of stuff out there
that uses undocumented opcodes, but I sure haven't seen it!

The one trick I _have_ seen is the JSR-to-last-byte-of-page, but
that 6502 bug was fixed in the 65C02, so //c's and enhanced //e's
wouldn't be able to run even _those_ programs!

Since there has been little outcry about //c and //e game compatibility,
I conclude that undocumented opcodes are not a major issue.

Does anyone have a list of programs that are so affected?

-michael

===============================================================
This is my personal opinion, and does not in any way represent
the position of my employer, etc...