Re: R65C02 PI

[johnlb@primenet.com (John Bowling)]

In article <4vh2j7$8kq@darla.visi.com>, Nathan Mates <nathan@visi.com> wrote:
>In article <4vgvr3$na8@nnrp1.news.primenet.com>,
>John Bowling <johnlb@primenet.com> wrote:
>>In article <4vd6qq$8qt@newsbf02.news.aol.com>, W12Ste <w12ste@aol.com> wrote:
>>>In my IIe I found a 'R65C02 PI' with '65402-3' on the bottom is it a
>>>standard 6502???
>
>>It's a Rockwell 65C02.  It will work as a standard 6502, but may *not*
>>properly replace the 65C02 in an Apple IIc or IIe.  Most software should
>>work, but some code that is expecting the WDC 65C02 enhancements may break
>>on the enhancements that Rockwell put into their version.
>
>   Bzzzt! Referring to Lichty & Eyes book on the 6502, 65C02, 65802
>and 65816, p. 561, shows that the Rockwell 65C02 is a _superset_ of
>the regular 65C02. In other words, it's a WDC 65C02 _plus_ a few (32)
>more instructions of their own.
>
>   Where the incompatability shows up is that the opcodes used by
>those 32 extra instructions are 1) treated as NOPs by regular 65C02s,
>and 2) Have wildly different meanings on the 65802/65816. Thus, code
>using the extra features of the R65C02 won't run correctly on anything
>but a R65C02.
>
>   In case I haven't quoted enough from Lickty & Eyes's book the past
>week, I'd really encourage anyone who wants to comment on the guts of
>the 6502, 65C02, R65C02, 65802 and 65816 chips to pick up a
>copy. There was a rumor that WDC was selling [photo]copies a while
>back; anyone care to confirm or deny it?

I should read mine more often.  They have them as photo copies, 8.5 x 11,
with errors in the published book corrected.  I have both.

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

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- John Bowling          -- Shouldn't you be commuting by bicycle?
- johnlb@primenet.com   -- No, that's not a valid excuse!
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