RE: Synertek 6502 compatibility

From: Rob Clarke <>
Date: Thu, 12 Apr 2012 13:26:38 +0200
Message-ID: <>
My thought was also that it might be BCD related. I have not performed any
further tests yet but as the PET otherwise booted OK and makes it as far
as the BASIC interpreter it must be some fairly esoteric function of the
processor. I would have thought it unlikely that it's an early revision
issue as this chip has a 1984 datecode. It also behaves the same way in
Mike's PetVet, so I can rule out ROM/RAM issues.

It it's interesting to me that the kernal evend renders the bytes free as
a FP value.

Is there a basic 2 rom dissasembly kicking around somewhere?


> Hallo allemaal,
>> it was due to an error in my emulation of rol/ror or lsr.
> It just triggered this: IIRC the very first 6502s had a bug in ROL/ROR.
> Is it possible that Synertek produced some with the same bug?
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Received on 2012-04-12 12:00:10

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