Re: 6526A synchronous serial behavior?

From: Gerrit Heitsch <>
Date: Sat, 24 Sep 2011 17:07:11 +0200
Message-ID: <>
On 09/24/2011 04:28 PM, Nicolas Welte wrote:
> Segher Boessenkool wrote:
>>> The interesting question is... Does the 8521 behave like a 6526 or
>>> like a 6526A?
>> 6526A means a 6526 that runs at 2MHz. It has nothing to do with
>> die revision. There seems to be a strong correlation though, most
>> later chips were 2MHz and most older were not.
> Yes this is very unfortunate. The scene seems to refer to the different
> timing versions with the A suffix, while in reality it is the speed
> grade. I found the change came in late 1986, the earliest "new" version
> I have has a date code of late 1986. This also matches with the arrival
> of the reportedly incompatible C128DCR and Aldi-C64 versions.

This also matches the appearance of the 8521 in late 1986. Could it be 
that the change in timer behaviour is due to a mask change done while 
transfering the 6526 from NMOS to HMOS-II?

I wouldn't put it beyond Commodore to just drop the '8521' marking after 
a short time and just mark them '6526' again. The 'A' (2MHz) would then 
be a sideeffect of HMOS-II allowing higher speeds.


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Received on 2011-09-24 16:00:04

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