Hi, Ethan Dicks schrieb: > On 9/16/10, Rhialto <rhialto@falu.nl> wrote: >> On Thu 16 Sep 2010 at 10:38:30 +0200, "André Fachat" wrote: >>> I voted for the 6522 as next chip to analyze, to find out about the >>> shift register bug. >> >> Speaking of shift register bugs: there is this one that I don't remember >> being explained. If you enable sound on a PET, then try to load anything >> from cassette, the PET hangs. The STOP key does not work, nor does >> anything actually load. this is _the_ 6522 shift register bug that also was the main cause for the 1541 being throttled that much. And it has been exaplined in depth. I cannot tell you the exact forum link at 6502.org, but I believe it was Garth Wilson who gave a thorough explanation how a decent state of the Phi clock affected sampling of the serial input, when external clocks were used. Have a search there. > Yes. I remember that one (especially since a lot of my early work was > fiddling with CB2 sound and I didn't own a disk drive). > >> See >> http://www.commodore.ca/manuals/commodore_pet_2001_quick_reference.pdf >> which also notes "NOTE: Location 59467 must be reset to zero for >> cassette to function properly". But that shift register isn't used for >> cassette loading, right? > > It's not, but ISTR some vague stories about putting the shift register > into free-running mode (which is how one gets sound) triggers some > hidden problem. I'd love to know what is _really_ going on in there > (not that we could fix the problem). > > I'm suddenly curious if the 65C22 has the same issue (I have a few of > each; I should try it). The 65C22 did not fix that bug to my knowledge, but CMD used the 65SC22 in their FD2000 series of drives and they implemented the Fast Serial mode (Burst commands known from the C128, 1571, 1570 and 1581) with exactly that chip. So this chip is not affected by the bug. By the way I think it was also in 6502.org where a simple workaround is described that ensures that serial input sampling is delayed a bit, when Phi is in a state that does not allow for reliable sampling. Womo -- ------ to obtain more infos about me, look up the page ------ ------ http://www.wmsr.de | wm (at) wmsr (dot) de ------ Message was sent through the cbm-hackers mailing listReceived on 2010-09-16 21:00:04
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