68kMLA Classic Interface

  SetVCC(1);

  digitalWrite(PIN_CE, 1); // cs = deassert
  digitalWrite(PIN_RESET, 1); // reset = assert / OE = deassert
  digitalWrite(PIN_SEREN, 1); // disable serial interface
  digitalWrite(PIN_CLK, 0);
  BitDelay();

  digitalWrite(PIN_CE,0);
  digitalWrite(PIN_RESET,0);
  BitDelay();

  int i = 0;
  while (digitalRead(PIN_CEO)) {

    Serial.print(digitalRead(PIN_DATA) ? '1' : '0');

    digitalWrite(PIN_CLK,1);
    BitDelay();
    digitalWrite(PIN_CLK,0);
    BitDelay();
   
    i++;
  }
  Serial.println();
  Serial.println(i);

The CC logic board that is confirmed to work with the Sonnet Presto that @zigzagjoe has is PN 820-0367-C, photos attached. The Presto came in this machine when I bought it, so unfortunately I don't know any history of the board beyond that.

This spurred a good idea, thank you. Bolle and I have been brainstorming and pouring through schematics; my working theory is perhaps something's going terribly awry at handover to the Presto/Tokamac 040, perhaps there might be some issue with bus mastering on the Color classic. So few cards actually used bus mastering on the LC slot an color classic specific errata could have went unnoticed until a chipset or board revision fixed it. I am only aware of one card (apple 820-0532) that does bus mastering in the conventional sense (not like an accelerator).

So to that end I'd like to see some more pictures of boards known to work or not work so we might check board revisions.

Keep in mind I have made a Presto and it wouldn't work in my early LC (with the big fat Cap on the SCSI chip). I sent it to... Max? And It worked fine for him.

The issue might not be limited to CCs.