squibby@eleazar.dartmouth.edu (Clark L. Breyman) (03/07/90)
Someone( I lost that article) posted a question on changing the ACIA clock divide for the MIDI port and winding up with 500KHz. I hope this is possible, as it would (with Fred Brooks's MIDINET) provide a wonderfull built in networking facility. Unfortunately, MIDI was designed for musical applications where noise free operation was optimized over bandwidth. This means that, in order to avoid ground loops and the hum that comes with them, all MIDI is opto-isolated Current leaves one machine. goes through an LED on the slave and returns to the master. The two devices are electrically independant. An 500KHz sounds to me a lot faster that most opto-isolators can handle. Anyone got specs on the OI's in the ST? Along this line, it seems like this could be exploited by Atari the way appletalk was exploited by Apple. I assume Senor Small's in-progress board uses the serial port or the printer port. Perhaps a hardware bypass of the MIDI OI might be in order? ---------- Clark
dmb@wam.umd.edu (David M. Baggett) (03/07/90)
In article <20049@dartvax.Dartmouth.EDU> squibby@eleazar.dartmouth.edu (Clark L. Breyman) writes: > > Someone( I lost that article) posted a question on changing the > ACIA clock divide for the MIDI port and winding up with 500KHz. > I hope this is possible, as it would (with Fred Brooks's MIDINET) > provide a wonderfull built in networking facility. Unfortunately, > MIDI was designed for musical applications where noise free operation > was optimized over bandwidth. This means that, in order to avoid > ground loops and the hum that comes with them, all MIDI is opto-isolated > Current leaves one machine. goes through an LED on the slave and returns to the master. The two devices are electrically independant. An 500KHz > sounds to me a lot faster that most opto-isolators can handle. Anyone > got specs on the OI's in the ST? Whoa! Let's not get too excited; I was just asking if anyone had gotten this to work, not claiming I'd done it. The ST hardware registers seem to allow it, but this certainly doesn't mean the opto-isolators will tolerate it. I have not been able to prevent the machine from hanging in 500KHz mode. As I mentioned in the original post, this could be due to any number of things (e.g., OI's not up to that bandwidth, software interrupt in OS not fast enough, etc.) So far no one's replied "yes, I've gotten this to work" to my original post, although several people have said they have tried (among them Fred Brooks -- he's a step ahead of ya). It "sure would be neat" if it could work, but I haven't had much luck, and haven't heard from anyone who has. Maybe it's a well-guarded secret. :] Dave Baggett dmb@cscwam.umd.edu