Re: 6526A synchronous serial behavior?

From: Gerrit Heitsch <>
Date: Sat, 24 Sep 2011 14:18:14 +0200
Message-ID: <>
On 09/22/2011 10:35 PM, Groepaz wrote:

> so if you want to know what kind of cia you really have, run a program that
> tests the interrupt delay ( for example
> )

Thank you for the URL.

Did a test run on my systems and got the following:

6526   (1384)  is seen as a 6526
6526R4 (3583)  is seen as a 6526
6526   (3086)  is seen as a 6526
6526B  (4887)  is seen as a 6526A
6526A  (3089)  is seen as a 6526A  (*)
8521R0 (4586)  is seen as a 6526A  (**)

(*) The 'A' is not part of the original marking, it was added

(**) That one came from a 1571 drive.

It's a pretty small dataset, but it makes me wonder whether Commodore 
intended to use the 8521 as the 6526 replacement in HMOS-II but later 
just continued to mark the CIAs used in C64 and C128 '6526A' no matter 
what was in there. Maybe ot avoid confusion?


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Received on 2011-09-24 13:00:03

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