Posted By
indi
on 2006-07-21
07:07:01
|  UNdocumented instructions....
Some quick questions....
How stable are they?
Are they available on ALL makes/models of the Plus/4?
Has anyone ever reported one not working, or different results?
Which are the most dependable?
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Posted By
AmiDog
on 2006-07-21
15:06:55
| Re: UNdocumented instructions....
I usually visit http://unusedino.de/ec64/technical/aay/c64/ibmain.htm for information about the 6502 and illegal instructions.
The only information I can find about differences between 6502 and 7501/8501 is that there are none when it comes to (illegal) opcodes.
"All these CPUs are opcode compatible (including undocumented opcodes, except the 8502, where some differences concerning the undocumented opcodes have been reported)." http://en.wikipedia.org/wiki/MOS_Technology_6510
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Posted By
indi
on 2006-07-21
16:03:42
| Re: UNdocumented instructions....
So does that mean that all undocumented ops are available ""and do the same thing"" on all plus/4's???
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Posted By
TLC
on 2006-07-21
17:34:28
| Re: UNdocumented instructions....
Hi Mike!, you might want to take a look at these articles:
http://www.oxyron.de/html/opcodes02.html
http://www.filegate.net/cbm/6-tech/pal_time.txt
In short, the situation is the same (AFAIK) on all models of the Plus/4, in the respect that those opcodes found to be stable are also stable on the 7501/8501, and the rest are similarly unstable like on the '64 or '128. I'm not aware of differences between the 7501/8501 or different revisions of the 8501... if two unstable opcodes behave differently on two Plus/4s, it's rather due to manufacturing tolerances, similarly to the '64 or the '128.
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Posted By
TLC
on 2006-07-21
18:02:51
| Re: UNdocumented instructions....
Hmmm, the second link should be http://www.ffd2.com/fridge/docs/6502-NMOS.extra.opcodes
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