Re: 6502 illegal opcodes

From: Groepaz <>
Date: Fri, 4 Nov 2011 22:27:21 +0100
Message-Id: <>
On Friday 04 November 2011, you wrote:
> Opcodes $8b and $ab are not predictable in that their result depends on
> various analog effects; their behaviour can vary on a single physical
> chip when it heats up, even.
these are predictable though - if you choose the right argument :) not that 
ane #$00 is terribly useful =P

> Various opcodes are unpredictable in the sense that their result depends
> on what happens on the data bus while RDY is low.
i would not call that unpredictable - on the c64 for example just make sure 
you dont execute them in a badline (or to be exact: make sure the vic does not 
try to fetch data while the opcode is executed), then they work predictable. 
they are just unpredictable in the sense that it is somewhat uncommon and 
unexpected that such thing would have an affect on the result of a cpu 
instruction :)


Ein Zyniker ist ein Schuft, dessen mangelhafte Wahrnehmung Dinge sieht wie sie 
sind, statt wie sie sein sollten. 
<Ambrose Bierce>

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