6502 CPU schematics

[Pete Turnbull]

On 07/03/2008 20:29, Philip Belben wrote:

> Well, I'm short of a 6520 PIA!  Have you any of those left?  If so, 
> please contact me off list.
> 
> When I was 13 (1980.  Ouch!) I was given a PET for my birthday.  A few 
> years later I blew up an output buffer in one of the 6520s trying to use 
> the Cassette 2 motor output as a controlled power supply.  We connected 
> one of those two-tone doobells that uses the back emf from the "ding" 
> solenoid when you open the switch to sound the "dong".  Said back emf 
> killed the output buffer on that pin of the 6520.  It managed to do so 
> without any noticeable damage to the intervening circuitry, too!

Common problem -- 6520s are fragile.  For that reason, it was common, at 
least here, to replace them with Motorola MC6821s, which was a later 
version of the MC6820, which is just the same as the MCS6520.  Lots of 
the PETs at the college where I worked in the early 80s had Motorola 
replacements because the 6821 seems to be more robust than the 6520.

So replacing the missing or damaged 6520 with a Motorola MC6821, which 
should be much easier to find, even has a degree of authenticity :-)

-- 
Pete						Peter Turnbull
						Network Manager
						University of York