Re: C64C case production molds resurfaced

From: Gerrit Heitsch <>
Date: Wed, 04 Mar 2015 21:13:52 +0100
Message-ID: <>
On 03/04/2015 09:03 PM, wrote:
> On 2015-03-04 20:47, Gerrit Heitsch wrote:
>>> Right - and quite similar to the 6526 in many respects. AFAIR it was
>>> something like a 6526 stripped from the timer(s) or so.
>> The 8520 had a normal timer instead of the RTC the 6526 had. That's
>> about it, you can use a 8520 in a C64 if the software doesn't use the
>> RTC.
> You mean the TOD?

Yes... Looks like they decided they don't need it for the Amiga but 
another timer/counter couldn't hurt.

>> Probably to keep customers from complaining... Especially since the 8521
>> is not quite the same, if I remember right the timer IRQ is one cycle
>> late compared to the 6526. Doesn't really matter most of the time,
>> unless you use it where the timing is REALLY tight.
> Hm... it's interesting that so many years after one thought he knew
> practically everything about the machine - there are still things to
> discover again and again :-))

I think there is a debugger that allows you to single step a program 
which needs such tight timing. The unpatched version is supposed to fail 
on a 6526A/8521 due to the IRQ or NMI arriving one cycle too late.

>> This little tool will detect the CIA (and other chips) you have in your
>> box, a 8521 will be listed at '6526A':
> And what if it is a 6526A? Or are all 6526As basically 8521s?


I have a few 6526A-1 (so labeled) and they are detected as '6526'. They 
also have a datecode before the end of 1986. Which to me, means that all 
6526 made 1987 and later are 8521 inside. So far that has checked out. 
They also run a bit less hot.


       Message was sent through the cbm-hackers mailing list
Received on 2015-03-04 21:00:39

Archive generated by hypermail 2.2.0.