Re: 8520/21

From: Gerrit Heitsch <>
Date: Fri, 06 Mar 2015 18:10:31 +0100
Message-ID: <>
On 03/05/2015 09:31 PM, Martin Hoffmann-Vetter wrote:
>> Remember, Commodore made a lot of different chips just because they
>> could...
> ...and need it.
>> Why a special CPU for the 264 series and the C128 instead of
>> just using a different bond out of the 6510? The 8500 is the 6510 in
> At this time, CSG build many chips in HMOS. So if Commodore need a huge package of CPUs, they build a new version in HMOS. This isn't a special CPU, it's a variant of an existing CPU in HMOS.

Well, the 7501/8501 ist a redesign from the 6510, it really lacks Bit 5 
of the I/O-port where the 6510 has all 8 Bits with only 6 of them bonded 
out. So it should have been possible to use it for the 264 as well, with 
just different bonding.

>> Or why the 6523 and later the 6525 (6523 with IRQs)? And
>> then all the 77xx-TTL replacements... Or the 6529...
> They need these chips. First they can buy it from an other manufactor. In any case, these chips are not available, so they build it self. What's the alternative for a 6529? It's a simple chip, so they designed it, build it und use it.

The way the 6529 is used in the 264 series is (from the code I know) 
write-only. So a simple 74LS374 should be able to do that job. Or, with 
the keyboard latch in TED what it is, you could have even gotten away 
with a 74LS244. Might have been a bit difficult to pass FCC though since 
you then have the buffered data bus on the keyboard matrix all the time.

It becomes a different issue when you need full I/O, but that came later 
when they used the 6529 also in the plus/4 for the user port.

Of course there are upsides of having a chip plant 2 doors down as 
well... After all, that's how we got VIC and SID.


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Received on 2015-03-06 18:00:05

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