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From: sinclair@aero.ARPA (William S. Sinclair )
Newsgroups: net.music.synth,net.micro.atari
Subject: MIDI on the Atart ST
Message-ID: <363@aero.ARPA>
Date: Thu, 15-Aug-85 14:42:23 EDT
Article-I.D.: aero.363
Posted: Thu Aug 15 14:42:23 1985
Date-Received: Mon, 19-Aug-85 22:32:05 EDT
Reply-To: sinclair@aero.UUCP (William S. Sinclair (5435))
Organization: The Aerospace Corp., El Segundo, CA
Lines: 13
Xref: linus net.music.synth:408 net.micro.atari:962

I took a peek at the schematics provided by the Atari ST developers' kit.
The MIDI interface is essentially a Motorola 6850 ACIA driven by a SHARP
900 opto-isolator. Output apperas to be standard open-collector logic.
Ther are actually TWO 6850's in the box. The second goes to an output port
directly. I don't know for what purpose.
 
As far as I/O addresses, the chip select comes from the "glue" chip, so it's
not obvious what they are. I couldn't find a refernce to the addresses in the
ducumentation either. Perhaps the developers package contains a more detailed
I/O memory map, but I haven't found it yet.
 
                                      Bill Sinclair   213/647-1753