Re: Disabling memory refresh in UltiMax mode Re: 6510 handling of $00 and $01 registers

From: Segher Boessenkool <>
Date: Sun, 11 Dec 2011 12:34:15 +0100
Message-Id: <>
>>> Back then the CIAs were also labled 6526R4. MOS dropped the 'R4'
>>> later. Gives you an idea how long it took to get those working. :)
>> Not terribly long IMO. They shipped earlier revisions than that.
> Those must have had some kind of bug though, or why would MOS start  
> a new revision?

There are many reasons...  Yield, timing tunings (which is also yield,
it gives you a better sort), or indeed fixes for (perhaps critical)

> The oldest CIA I have so far is a 6526R4 with a 2383 datecode.

The oldest I have heard of is week 14 of 1983; those come without
the R4 marking.  Some time in 1983 or 1984 they switched to without
R4 marking again (what revision is in there, I have no idea).
The last weeks of 1985 got us the 6526/S (whatever that is), and in
1987 they switched to the 8521 (marked as 6526A, 216A).


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Received on 2011-12-11 12:00:03

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