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From: shri@ncst.ernet.in (H.Shrikumar)
Newsgroups: rec.music.synth,comp.sys.ibm.pc.hardware
Subject: Re: MIDI
Message-ID: <1120@shakti.ncst.ernet.in>
Date: 26 Nov 90 05:39:53 GMT
References: <4900.tnews@basso.actrix.gen.nz>
Reply-To: shri@ncst.ernet.in (H.Shrikumar )
Followup-To: rec.music.synth
Organization: National Centre for Software Technology, Bombay, INDIA
Lines: 45

In the discussion on rs232-to-midi interfaces ...
    dgold@basso.actrix.gen.nz (Dale Gold) and
    herbie@bruce.cs.monash.OZ.AU (Andrew Herbert) contribute:

dgold> A friend of mine has built an IBM interface based roughly on my homemade
dgold> Amiga box. 
dgold> [...]

herbie> Isn't there a problem getting an ibm serial port to spit out 31.25kbps
herbie> as required by midi?

dgold> I believe so. I know he had to do some fiddling with the clock speed or
dgold> something. I'll ask him and post anything useful he might have discovered


   I have been thru this stage, so I thought I'd answer this FAQ...

 The standard 8051 (?) Serial interface in the IBM PC, using a 1.84 MHz
Xtal can generate 19.2Kbps or 38.4Kbps. But to get it to generate
the MIDI baud rate, what needs to be done is a "simple" (if you
are adept with a soldering iron) change of the crystal on the serial
interface board to a 1MHz or 2 MHz unit. This will enable the software
to set it to 31250 bps by doing what you'd normally do to set it at
38.4Kbps or 19.2Kbps respectively.

  If the serial clock is generated from the system clock on the
mother board (if serial interface is on mother board) ... then it is
more difficult.

 Having done this, you get a +-12V, 31250 baud serial stream, set to
8bits, no parity. An external box (like the ones with an Amiga) will
convert the +-12Volt to a 5mA current loop for output, and an opto
for the input. Done. This method works, only needs careful soldering.

  Now I have a question ... could some one describe to me what the
Roland MPU-101 looks like ... is it a card you plug into the PC, or
is it a box you connect to a normal RS232 port ?

  If the latter, I am sure you can connect a MPU101 to a SUN or
pretty much any computer, as long as you write the software for it.
Anybody used a MPU101 with anything but an IBM-PC ?

 TIA.

-- shrikumar ( shri@ncst.in )