Re: Synertek 6502 compatibility

From: Segher Boessenkool <>
Date: Wed, 11 Apr 2012 01:33:56 +0200
Message-Id: <>
> Does anyone know if the Synertek 6502 is 100% compatible with its  
> MOS cousin?

They are.  That is, what is "compatible"?  If it means "implements
the same specifications", they are compatible.

Synertek got the mask sets from MOS, and they only changed things
in the periphery, probably because they had a different silicon
process (they resized the resistors, for example).  Electrically
they will behave slightly differently, but no single individual
chip is the same anyway, and they should be within spec too.

> I know some of the later CMOS incarnations did not have the same  
> behaviour with undefined op-codes but a) this a 1984 chip and b) I  
> can't believe the PET kernal would use them anyway.

There are only two undefined ops that depend on analog behaviour
($8b and $ab from the top of my head), and those certainly aren't
used in the kernal.

> It is also possible that this chip is just duff of course.

_Something_ is broken, sure :-)

It would be interesting to find out what it is.  Since it sounds
like your box is sort-of working, you could run some test programs?


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Received on 2012-04-11 01:00:05

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