Ethan Dicks wrote:
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?
The issue with using the shift register for the Commodore serial bus is
that if you feed the clock directly into CB1, it can violate the timing
specs. If you add an external synchronizer, that would fix it.
However, instead they went the cost-reduction path of bit-banging it.
Another
"bug" people claim... caused problems with using the 6522 in
68000 systems.
Did Apple do something tricky with the original Mac design?
I seem to recall that they did, but it's been so long since I looked at
the schematics and the reverse-engineered PAL equations that I don't recall.
Eric