On Sep 22, 2011, at 12:57 PM, Wolfgang Moser wrote: > Nate Lawson schrieb: >> On Sep 21, 2011, at 3:22 PM, Segher Boessenkool wrote: >> >> It's 500 Kbit/sec inbound to the 1571. Some devices receive it just >> fine, others don't. I'm going to try reducing the clock rate slowly >> and see where it becomes reliable. If it truly is synchronous with > > if it is different behavior from drive to drive then this let's me think > on different CIA revisions. 6526 vs. 6526A vs. 8520, you know even VICE > does support two different 6526 types, the "old" and the "new" one which > have some off-by-one clock cycle differences. I don't know about the > exact details, but since the shift registers may be the worst > studied/tested functional blocks of the CIA, this could be a reason. > > Maybe you want to have a look for a piece of CIA type detection code and > check, if there is a relation beweeten "unreliable" 1571 drives and a > certain CIA type. I would think all 1571 drives have a 6526A because they have to run at 2 MHz. The 6526 can only do 1 MHz. As for the 8520, it would be strange to move to the HMOS line in only this chip. Also, you have to remember the 1571CR, where the 6526 was merged into a single chip with the WDC logic. I have no idea how that will perform for 500 Kbit/sec serial. -Nate Message was sent through the cbm-hackers mailing listReceived on 2011-09-22 21:00:22
Archive generated by hypermail 2.2.0.