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From: kahrs@alice.UUCP (Mark Kahrs)
Newsgroups: net.music.synth
Subject: MIDI
Message-ID: <3416@alice.UUCP>
Date: Fri, 22-Feb-85 20:40:27 EST
Article-I.D.: alice.3416
Posted: Fri Feb 22 20:40:27 1985
Date-Received: Wed, 27-Feb-85 03:01:29 EST
Organization: Bell Labs, Murray Hill
Lines: 24

With all these postings about MIDI and RS-232 I thought I'd put in my
$0.03 worth. First off, the clock rate is 31.25 kBAUD.  Now, all you
RS-232 fans out there may recognize the fact that 31.25 KB ain't
exactly standard. Right. As Dave Sewhuk pointed out, UARTs take
a 16x clock, so 16 * 31.25 gives you 500 Khz. So, some person had
this extra 500 Khz clock and decided to foist it on the rest of us.
So much for straight conversion.  Also, as Dave Hsu pointed out,
the MIDI standard requires a current loop interface, hence an opto-
isolator.

Now, it's definitely true that Roland makes the MPU-401 which enables
a micro to talk MIDI but their documentation leaves MUCH to be desired... Another
possibility is to use the Mac output port with some
external circuitry and an external clock.

Anyhoo, hope that helps someone.

I'm delighted to see this group!

Cheers,

Mark.