Re: CIA 6526 vs 8521

Date: Thu, 05 Mar 2015 23:24:53 +0100
Message-ID: <1548540.Fvp6Oj0ZQB@rakete>
On Thursday 05 March 2015, 19:30:31 Gerrit Heitsch <> 
> 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.

one of my C64s had a 6526(not A or B) with "new" behaviour - that was what 
made me investigating this issue some more back then (until then, i only saw 
6526A with that behaviour myself as well) :)


Es geht nicht darum, dass wir zu einem Überwachungsstaat werden, sondern 
lediglich darum, zu speichern, wer wann mit wem und wo telefoniert hat. 
<Mechthild Ross-Luttmann, CDU>

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Received on 2015-03-05 23:00:05

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