Re: 8520/21

From: Gerrit Heitsch <>
Date: Sat, 07 Mar 2015 09:11:09 +0100
Message-ID: <>
On 03/07/2015 12:31 AM, Jim Brain wrote:
> I can understand the 6529, since it offers significantly less feature
> than the 6522/6526 and bean counters would note that a half functional
> 6522 could be squeezed into a far smaller die if redesigned.  I can also
> understand the 6526 working to fix the issues with the 6522.

The 6529 looks like they took just the data register and the output 
drivers for port A of a 6522 and made it into a stand alone chip. Should 
be a VERY small die or a die with lots of unused space.

BTW: Can you still use the shift register in the 6526 as a sound 
generator like you could with the 6522 (CB2 sound in PET)?

   The 6510
> was a substantial upgrade from the 6502, with the BA/AES functionality
> and the on chip register, though I suppose one could argue the point.

The 6502 already had BA/RDY, it just lacked the tristate buffers for the 
adress lines and R/W. For what the 6502 was originally intended that 
didn't matter, for a shared bus design it meant additional buffers that 
cost money (see VIC-20).


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Received on 2015-03-07 09:00:05

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