mikec@wheaties.ai.mit.edu (Mike E. Ciholas) (07/09/90)
Synopsis: The SID-II does not work with the SE, II, IIx, IIcx, IIci Solution: Looking from the rear of the mini DIN 8 connector, cut the pin 7 lead (which is in the center). Result: The SID-II will now work with all the above computers. The IIfx is still unresolved at this date. Description: (I've been awake many nights looking for this, so forgive me if I don't make the clearest sense) It turns out that the serial ports on all but the classic macs are just ever so slightly different. The difference comes in pin 7 of the connector which is used a GI (general input) pin. The line is connected to a differential receiver in the mac that is connected to the DCD (data carrier detect) line that can interrupt the processor. Well, I tied the line to ground, figuring that would be better than having it float. Bad move. It seems that the differential receiver in the Mac has only a few millivolt difference input. So just the little noise that the signal picks up in the cable causes the DCD input to interrupt the processor constantly. When the input is left unconnected, it floats to a voltage level that is a volt or so from the transition range, thus doing no harm. And guess what. It doesn't happen to every computer either. Some have inputs that are just insensitive enough to not pick it up. Honest, I tested it on several computers before I shipped, and had to test on twenty more after wards to find one that didn't work. So there it is...problem solved. Sorry for the problem, just trying too hard, I suppose. (checkout sumex-aim.stanford.edu, file: info-mac/sound/program/sid-ii.hqx for more info. Anonymous ftp) Mike Ciholas mikec@ai.mit.edu