On Tue, Jun 18, 2019 at 2:28 PM Mike Stein <mhs.stein_at_gmail.com> wrote: > ----- Original Message ----- > From: "Ethan Dicks" <ethan.dicks_at_gmail.com> > Sent: Tuesday, June 18, 2019 1:55 PM > > On Tue, Jun 18, 2019 at 12:35 PM André Fachat <afachat_at_gmx.de> wrote: > > I THINK you can just use the 8250 board as reference. It is a universal > > digital board and is supposed to be jumperable to 4040 mode. > > Hi, Andre, > > Good point. Thanks for mentioning this. I'll check those pages in a bit. > ================== > > 8050 board also looks the same (note non-standard pin numbers!): > > 1 ODD HEAD > 2 HD SEL 1 > 3 MTR0* > 4 WP0 > 5 ACT LED 0 > 6 WP1 > 7 MTR1* > 8 ACT LED 1 > 9 SIB > 10 GND > 11 GND > 12 HD SEL 0 > 13 WRITE ENABLE > 14 DATA OUT > 15 DATA IN > 16 RD INHIBIT > 17 SOA > 18 SOB > 19 SIA > 20 GND Looking at this, let me suggest pins 9, 17, 18, and 19 should be S1B, S0A, S0B and S1A (middle char 0/1 not O/I) for drive 0 and 1 (it can be hard to tell looking at the hand-lettered prints with no context, Only one of the schematics I was looking at had a slash on the 0). In the 4040 schematics, I could find no references of J2-1 (noted as "ODD HEAD" above") which makes sense for single-sided drives, but neither could I find a mention of J2-20 (GND). The rest I was able to match up. I did find "ODD HEAD" on the 8050/8250 digital board schematics with jumper E3 (8050: Open, 8250: Closed, which also makes sense). The 4040 analog board (320816) shows connections for only 16 of the 20 pins: 2-9, 12-19. Nothing mentioned for 1, 10, 11, or 20. I did easily find references to 1, 10, and 11 on the 8050 schematics. Perhaps J2-20 is N.C. on the 4040 board and GND on the 8050/8250 board. No harm to tie it to 10,11. Thinking of my original task, things match up fairly well between J2 signals to the CBM analog board and a "regular" SA400/SA390 drive 34-pin Shugart floppy interface except for wondering why Commodore made the drive activity lights controllable under software (not tied directly to Drive Select as they are in the Shugart analog board), and the difference between S0A/S1A counting 0-3 or 3-0 vs step/direction controls on the stepper. I see how the SA400 implements step/dir (2-23 in the SA400 Minifloppy Service Manual) but it seems that the circuit to remember the present state of S0A/S1A and compare it to the new state of S0A/S1A to derive direction (and trigger a step) is more complicated than bypassing the SA400 step/dir counter/state machine and re-implementing the Commodore analog board stepper driver ('LS139, '06, 4x 1N4003, and FPQ3724/ULN2704B or 2x 2N4401/2N4403 pair). The SA390/SA400 Shugart analog board appears to have 2x 75452 drivers for the stepper phases and the IN4003 back-EMF diodes already, so perhaps removing the 75452s, socketing them on the Shugart analog board, then moving them back to a new board between the CBM digital board and their old spots and reusing them in place of the FPQ3724s/ULN2704Bs (adding in the 'LS139 to fan out S0A and S0B to the four inputs of the 75452s) might be a simple, reversable mod to the SA400 I have. It's not quite a full J2->34-pin adaptation but it's pretty close and it's simple. It shouldn't be hard to whip up a board with a 20-pin interface back to the digital board and a 34-pin Shugart interface for the SA400 with a couple of DIP plugs for the 75452s at 4D and 4E. Might need a 78M05 to feed the 'LS139. It probably wouldn't be much harder to run two SA400s from that new board, just need a second 'LS139 and room for its 75452s. Also might need a buffer to drive the shared read/write/control lines on both drives from the digital board just to be on the safe side. -ethanReceived on 2020-05-29 21:57:23
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