Re: 6502 illegal opcodes

From: Segher Boessenkool <>
Date: Fri, 4 Nov 2011 20:08:11 +0100
Message-Id: <>
>> are they reliable from a 6502 to another  ?  (for example   mos vs
>> rockwell vs synertek)
>> or between 6502, 6509, 6510 ?
> Yes, they are all present in 6502/6509/6510/7501/8501/8502. They  
> are not
> present in CMOS 65C02, but it did not make into any production  
> Commodore
> machine. Don't know about Rockwell & Synertek :-(

Opcodes $8b and $ab are not predictable in that their result depends on
various analog effects; their behaviour can vary on a single physical  
when it heats up, even.

Various opcodes are unpredictable in the sense that their result depends
on what happens on the data bus while RDY is low.

Rockwell and Synertek parts behave identically to MOS parts, except for
the analog behaviour (they are made on different processes); same for
6502 vs. 8500 etc.


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Received on 2011-11-04 20:00:03

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