Re: [stella] 6507 vs. 6502

Subject: Re: [stella] 6507 vs. 6502
From: Nick S Bensema <nickb@xxxxxxxxxxxx>
Date: Tue, 30 Sep 1997 12:04:48 -0700 (MST)
>Greg miller writes about the jmp (indirect) instruction:
>> Small note: I'm not sure about the 6507, but the 6502 and many of its variants
>> won't work properly, if a pointer in the table crosses a 256-byte page
>> boundary. Make sure your tables are either word-aligned or don't cross pages,
>> unless someone (Jim?) knows for sure whether the 6507 has this bug.
>The 6507 is *exactly* the same chip as the 6502 except it's put into a
>package with fewer pins to save a few cents on plastic and circuit board
>real estate.  It has the same bugs and undocumented instructions  ;)

The questions remain of exactly which undocumented instructions?

As I recall, throughout the 6502's lifetime, the undocumented opcodes
changed somewhat.  Do the same ones work on a six-switch 2600 as on a
four-switch or 2600jr?  Or 7800, even?

I'd hate to have to doom prospective buyers into constantly searching
thrift stores for the 2600 that will play a game using this kind of hack.
Especially those who already had to make a similar search when their
7800 didn't like the Supercharger.

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