Re: C64C case production molds resurfaced

From: Gerrit Heitsch <>
Date: Wed, 04 Mar 2015 20:47:55 +0100
Message-ID: <>
On 03/04/2015 08:34 PM, wrote:
> On 2015-03-04 20:20, Gerrit Heitsch wrote:
>>>> VIC is not that much of a problem. Despite the 6569 running quite
>>>> hot it doesn't die very often and there are still lots of them
>>>> available. TED is a different story since not as many were made
>>>> and the earlier ones (R1 and R2 with '84 datecode) seemed to die
>>>> easily.
>>>> I'd be more worried about the availability of the 6526 / 8521.
>>> 8520?
>> No, the 8520 is the CIA for the Amiga.
> 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.

>> (I own a 250466 board with a 8521R0 on U2 and a 1571 with one ).
>> Later Commodore went back to the '6526' label,
> That explains the scarcity.

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.

This little tool will detect the CIA (and other chips) you have in your 
box, a 8521 will be listed at '6526A':

>> The CIAs are not as easy to implement as one would expect. Digitally
>>  yes, but then there's the analog side (the way the output drivers
>> behave) that will be hard to duplicate with todays technology.
> ? Interesting. I always thought of 6526 in the digital domain only. What
> was so peculiar about the 6526's output drivers.

They were NMOS... You could do things to them that you don't want to do 
to CMOS output drivers. Like set the pin to HIGH and then pull it LOW.

Take a look at the datasheet for the MOS 6522 to see how the output 
drivers were set up.


       Message was sent through the cbm-hackers mailing list
Received on 2015-03-04 20:04:07

Archive generated by hypermail 2.2.0.