RE: 6502 illegal opcodes

From: Didier Derny <>
Date: Fri, 4 Nov 2011 20:57:56 +0100
Message-ID: <001801cc9b2c$0bf9d350$23ed79f0$@org>
Thanks, all I'll try to create something conform with the behavior of the

The code will be available in a few month :)

I restart from and old emulation I wrote in 1986 for apricot PC but at that
time it was too slow
The basic started but extremely slow, and the keyboard interrupt were not
really working.

I'm recoding it from C to avr assembler.
All 6502 registers are directly mapped to avr registers
As I have 128k of flash I'm using a lot of tables, almost no call (too
costly in cycles)
Abuse of macro :)  to avoid to simplify the writing...


-----Message d'origine-----
De :
[] De la part de Segher Boessenkool
Envoyé : vendredi 4 novembre 2011 20:13
À :
Objet : Re: 6502 illegal opcodes

> Those companies were licensed to make the chips based on the same  
> design
> in order to be a second-source option, so I assume the die is  
> identical.

It is almost identical.  I'm not sure if I have seen a Synertek chip;  
the Rockwell chips have a different layout around the pads, it looks  
to me
that they wanted more clearance around the pads (the MOS parts have much
less clearance than anything else I've seen).  There is also an extra
(redundant) contact from metal to active area, on the DBE signal.   
Oh, and
the Rockwell chip has the ground pads doubled, and it has different test

For most purposes, the chips are identical.


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Received on 2011-11-04 20:00:18

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