Re: CIA 6526 vs 8521

From: Gerrit Heitsch <>
Date: Thu, 05 Mar 2015 19:30:31 +0100
Message-ID: <>
On 03/04/2015 11:09 PM, wrote:
> however, 6526A are selected regular 6526 that just happen to work at 2mhz, its
> exactly the same die as regular 6526 (or 8521 for that matter). there are 6526
> labelled chips with 8521 die in them (shows the timer irq difference) and
> there are 6526A with the regular 6526 die in them (does not show the timer irq
> difference). thats why we changed it into "6526 (old)" vs "6526 (new)" in
> VICE, using the "A" suffix to indicate this difference is not only formally
> wrong (it means "2 mhz") but also does not (always) work in practise.

What added to the confusion was that most (if not all) HMOS-II CIAs were 
able to run at 2 MHz and therefore were stamped '6526A' or even '6526B'. 
I have yet to see a 6526 in HMOS-II without the 'A' or 'B'. Sometimes it 
was stamped on the chip later and is therefore not fully aligned with 
the numbers, but it's there. The NMOS 6526 were mostly 1 MHz types with 
no additional letter.

So it's easy to see how the thing about 6526 and 6526A started.


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Received on 2015-03-05 19:00:55

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