On Sun, May 30, 2010 at 10:30 PM, Eric Smith <eric at brouhaha.com> wrote:
Ethan Dicks wrote:
Were there any versions of the 6522 (65C22?) that had the shift
register bug fixed?
Yes. ?Some, but not all, of the CMOS variants fixed the issue. ?You can't
count on a part marked 65C22 as having the fix; you have to check the
datasheet for the specific manufacturer and part number.
Good to know (but not unsurprising).
Note that the issue isn't really a bug in the
strict sense. ?According to
Synertek application note AN5, the problem occurs when the rising edge of
CB1 occurs less than 100 nanoseconds before the falling edge of Phi2...
OK. I can accept is isn't strictly a bug, but what is it about the
VIC-20 design that violates the 6522 specs? Did they cost-reduce too
many corners? Is there a similar issue with the PET design?
I thought there was also a problem (verifiable with PETs) where
certain aspects of the chip act funny if you are using the shift
register - the symptoms I remember is that if you are using CB2
"music" (free-running shift register), the tape drive doesn't work.
You have to "disable the sound" before you can save your work (as we
used to view it when we were hacking PETs). Is this the same/a
related bug or something else?
Another "bug" people claim... caused
problems with using the 6522 in
68000 systems.
Did Apple do something tricky with the original Mac design?
http://farm3.static.flickr.com/2365/2391525329_af71ed4f8d.jpg
(one of the few times I've seen a 6522 hung off of a 68K - for an
embedded product I worked on in the 1980s, we had Z8350 SIO chips and
6821 PIO chips, but not 6522s).
-ethan