Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!samsung!aplcen!haven!wam!dmb
From: dmb@wam.umd.edu (David M. Baggett)
Newsgroups: comp.sys.atari.st
Subject: Re: 500KHz Midi; Author please reply
Summary: OK, here's a reply
Message-ID: <1990Mar7.041658.10020@wam.umd.edu>
Date: 7 Mar 90 04:16:58 GMT
References: <20049@dartvax.Dartmouth.EDU>
Sender: usenet@wam.umd.edu (USENET Posting)
Reply-To: dmb@wam.umd.edu (David M. Baggett)
Distribution: usa
Organization: University of Maryland at College Park
Lines: 30

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