The problem is described in Synertek's 6522 data sheet. On Sun, 3 Apr 2022, Rhialto wrote: > On Fri 01 Apr 2022 at 14:30:13 -0500, Jim Brain wrote: >> http://www.zimmers.net/anonftp/pub/cbm/faq/trivia/cbm-trivia-08.txt >> (question $07b) > > from that: "We early PET/CBM freaks knew, from playing music, that there > was something wrong with the 6522's shift register: it interfered with > other functions. The rule was: turn off the music before you start the > tape! (The shift register was a popular sound generator)." > > Do we already know why the shift register interfered with the tape? > > and, to remind people, do we already know why pressing the < button > while loading / scanning the tape for something to load would print > < characters to the screen if there was a signal on the tape? > > Neither are emulated in VICE (I think I tried it once) so it isn't > something that trivially occurs... > > Also, Compute #3, march/april 1980, mentions that sound > doesn't work if you have C2N #2 plugged in. Page 88: > > "NO CB2 SOUND? > > Larry Isaacs > > Some of you may have been unable to get the CB2 Sound, described in last > month's RAMBLIN', to function. Fortunately the most likely cause has a > very simple solution. Unplug the external cassette from the rear of your > PET. Having an idle cassette plugged into that cassette port grounds the > CB1 line on the 6522 IC in the PET. Grounding CB1 unfortunately stops > the shifting of the shift register used to generate the CB2 Sound. I > also checked a Synertek 6522 (PETs use MOS Technology) and found that it > had the same problem. It appears that this is inherent in the design of > the 6522, so keep it in mind when using the shift register for output. > > > -Olaf. > -- > ___ "Buying carbon credits is a bit like a serial killer paying someone else to > \X/ have kids to make his activity cost neutral." -The BOFH falu.nl_at_rhialto > wlevak_at_sdf.org SDF Public Access UNIX System - http://sdf.orgReceived on 2022-04-04 22:00:08
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