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From: rgc@wam.umd.edu (Ross Garrett Cutler)
Newsgroups: comp.sys.next
Subject: How to hook up a MIDI keyboard to your NeXTstation...
Message-ID: <1991May20.122642.25274@wam.umd.edu>
Date: 20 May 91 12:26:42 GMT
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Organization: University of Maryland at College Park
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Originator: rgc@avw.umd.edu
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Hello *,

I've seen numerous questions on the net in the last several weeks on
how to hook up a MIDI device to the NeXT.  This should probably go in the
FAQ since a lot of users might want to know this...  Personally, I called
NeXT several times about this and talked to numerous tech people; no
one knew how to do it except for $500 (for an expensive MIDI adapter)!
Even worse, they said they'd call back after they investgated it more...
two months later and still no reply...

Anyway...at least I got to learn a little about MIDI :-)

For the 030 systems, all you do is buy a MIDI adapter for the Mac.  I
recommend the Optcode MIDI Translator for $45 (Mac Zone).  A 
MIDI adapter is necessary because MIDI is a current loop and your serial
port isn't.  It consists of a few ICs (most importantly a Sharp PC-900 
opto-isolator) and a few resistors; you could make it yourself (the 
schematic is similar to the one given in "MIDI for Musicians" by C.Aderton)
but for $45 (premade), it's not worth it.

For the 040 systems (like mine), use the same adapter.  But since the 030's
use RS422 and the 040's use RS423, you're going to have to modify their
cable.  The basic difference between RS422 and RS423 is the former is a
differential (balanced pair) scheme while the latter still uses a ground.
Now the MIDI Translator expects a RS422 (like the Mac uses); you can
"convert" the RS422 type device into a RS423 device by grounding the
RXD+ and TXD+ lines; albeit crude, it works.

The pinout of the MIDI Translator is given below:
	1 Clock
	2 NC (no connections)
	3 RXD-
	4 NC
	5 TXD-
	6 RXD+
	7 NC
	8 TXD+

The pinout for the cable that comes with it is:
	Computer	MIDI
	1 R		Br
	2 Br		R
	3 G		O
	4 Y		Y
	5 O		G
	6 Black		Blue
	7 P		P
	8 Blue		Black

To make the above change, I opened up their cable and shorted the yellow,
black and blue wires together.  The resultant cable is symmetric.

I tested it on my NeXTstation running 2.1, hooked up to a CZ-1.  MIDI in
(e.g. using the CZ-1 as a controller for Ensemble) will actually work 
without the above hack, but MIDI out (using the CZ-1 as another 8 voices)
won't (unless you do the hack, of course).

Notes:
1. The MIDI Translator is self powered (it grabs power off of the line via
a capacitor).
2. I make no guarantees to the above.  It works for me...
3. I've noticed that Ensemble starts to crap out for complicated midi out's
(e.g. skynard32.mid -- see below); this is a bug in Ensemble...
4. For more details on RS422/RS423, see the excellent article "Welcome to
the Standards Jungle" in Byte, 2-83.
5. For details on MIDI, check out the midi* files in ucsd.edu.
6. For lots of MIDI files to play, see /music/midi in media-lab.media.mit.edu.


Hope this saves someone time getting there NeXT into the music world.
Believe me, it's definitely worth it!  Enjoy...Ross.
-- 
Please email -- I'll summarize.
Ross Cutler
University of Maryland, College Park
Internet: rgc@wam.umd.edu