Re: 6502 CPU

[spqr@ruth.uucp (Will Baguhn)]

pnt103@minster.york.ac.uk (Peter N. Turnbull (1Y0)) writes:

| Nathan Mates (nathan@cco.caltech.edu) wrote:
| : In article <3mbd1l$av@naurouze.cert.fr>,
| : Jean-Francois Fabre <fabre@puigmal.cert.fr> wrote:
| : >Does any of you know about the undocumented instructions on the 6502 ?
| 
| :    The 6502 does have some sort of undocumented instructions, but they
| : are not standardized. They can vary from one machine to the next, so
| 
| That's because different chip manufacturers made their 6502's in slightly
| different ways, and not all Apple 6502's came from the same manufacturer.
| 
| : there is no acceptible list of undocumented instructions. If you have
| : a 6502 (not 65C02) based machine (Apple ][, ][+, unenhanced //e), you
| : could by trial and error determine their behavior on your machine, but
| : it probably wouldn't work on any other 6502 machine.
| 
| Wrong!  The 65C02 made legal some of the undocumented 6502 codes, even
| adding some, and standardising them.
| 
| :    To make things worse, the 65C02 (used in enhanced //e, //c, //c+,
| : and the GS in emulation mode) has no useful undocumented instructions.
| : Anything unlisted acts just like a NOP ($EA), so you can put all the
| : undocumented instructions you want in your program, but it won't do
| : anything useful.
| 
| :    The Commodore 64 used a different processor (6510?), with
| : standardized undocumented opcodes; that's why programmers could
| : reliably use them.
| 
| This is not unrelated to the fact that Commodore owned a certain
| chip manufacturer.
| 
| Pete
| 

sit down and compare the instruction sets of the 6502 and the 6510.  
you'll find them remarkably similar... i'd even go so far as to say 
identical.  (in fact, i use a C64 programmer's reference manual instead 
ofa  6502 spec sheet for the opcodes and whatnot when i don't have a 
mini-assembler handy)

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