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 ones... With love from Austria (and many inofficial opcodes to try) Kurt Woloch -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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