Re: [stella] "Illegal" opcodes

Subject: Re: [stella] "Illegal" opcodes
From: kurt.woloch@xxxxxxxxx
Date: Mon, 19 Jun 2000 08:38:26 +0200
A. Davie wrote:

>But, their design spec says nothing about these other things - they
designed the hardware to the specs, and it meets the specs.  I >expect
books/manuals were printed long before actual hardware was available.  And
with the possibility of other manufacturers >making chips to those
specifications, you can't guarantee they will implement things on a hardware
level the same way.
>They COULD, for example, have made all "illegal" ops work like NOPs, and
still meet the specs.  Undefined behaviour is undefined >behaviour.  So
there's no way you "should" use those op-codes" - its just a lucky
>coincidence that a majority of 6502 variants work the same way.

Which, of course, raises the question if these "illegal" instruction, when
used in a 2600 game, will work on all 2600 variants, including clones like
the TV boy, or not. Maybe some of them use CPU by other manufacturers, which
do execute the official instructions correctly, but not all inofficial

With love from Austria (and many inofficial opcodes to try)
Kurt Woloch

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