Re: [stella] Undocumented opcodes

Subject: Re: [stella] Undocumented opcodes
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Mon, 20 Oct 2003 09:38:43 +0200
C. Bond wrote: 
> There are a few 6502 articles on the net which give the function and
> timing of miscellaneous undocumented opcodes. Unfortunately, the timings
> given for some opcodes, with indexing, do not seem to account for page
> crossing. According to the CPU model in the hardware manual, an extra
> cycle is almost certainly required in certain cases and some these do
> not agree with the numbers in the articles. Has anyone verified the
> cycle count for undocumented opcodes?

No, I haven't verified these, but I would be very surprised if the general rules 
wouldn't be valid for those too. If an index crosses a page boundary there
*must* be an additional cycles added.

And you can check e.g. the z26 source code for the implementation of all 
illegal opcodes.


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