6502 info.

-----Original Message-----
From: "mccullar" <mccullar@flash.net>
To: <vectorlist@synthcom.com>
Date: Wed, 14 Aug 2002 21:48:50 -0500
Subject: Re: VECTOR: Asteroids intermittent explosions

>
> Coincidentally, I've been soldering/desoldering on a couple of _Asteroids_
> boards this evening. Once in a while I see some very bizarre problems
> created by, of all things, the 6502 processor. Since this chip is socketed,
> and is easy to replace, why not see if that's the trouble? Tonight I
> replaced one that was totally dead; a couple of years ago I had one 6502
> that made the rocks jump around sporadically.
>
>
I used to deal a lot with 6502 stuff, i learned some VERY important stuff.

IF programmers dont screw around, and stick to the manual then everything is
fine BUT:

every manufacturer of 6502 used there own design in a fight to get beter
clock-rates.

this had the interesting effect of making unlisted opcode values have diferent
effects on different brands of cpu.

so if you suspect that a game is using illegal opcodes then try to use the
original brand of cpu.

of specific importance is to point out that there are MAJOR differences in
unlisted commands in the 65c02 c-mos version.

you should really avoid swaping c-mos for n-mos unless you are sure they are
used 'by the book'.

i was thinking at 1 point of using mame to check for illegal opcode useage.

c.u.

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Received on Wed Aug 14 21:45:40 2002