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Conference napalm::commusic_v1

Title:	* * Computer Music, MIDI, and Related Topics * *
Notice:	Conference has been write-locked. Use new version.
Moderator:	DYPSS1::SCHAFER

Created:	Thu Feb 20 1986
Last Modified:	Mon Aug 29 1994
Last Successful Update:	Fri Jun 06 1997
Number of topics:	2852
Total number of notes:	33157

1813.0. "In Search Of...MIDI on DEC machines" by VAXRT::GENTRY (Megan Gentry MLO5-5/E76) Wed Dec 14 1988 14:30

    I've been looking for some time into how to connect my MIDI
    synth to my PDP-11.  Since this might be of interest to those
    of you with PDP-11's or uVAX's, I'd like to toss out a few
    ideas and get reactions to them.  Each may attack a different
    aspect of the problem (31.25kbaud at 5ma?):

    1) Using a DLV11-KA EIA to 20ma converter, modified to do 5ma
       (or whatever MIDI requires), with added circuitry to supply
       the clock.

       Advantage is this box could then be attached to any DLV11-J
       port, which is an accepted module for both -11's and uVAXen.

    2) Use a DRV11 to send bytes to/receive bytes from a UART
       connected to the circuits outlined in the MIDI spec.

       Advantage is same as above as it could be connected to any
       DRV11.  Might require less hardware hacking to do.

    3) Use a KXT11-C coprocessor to handle the baud rate conversion
       (since it has a programmable baud rate interface), it could
       either handle all MIDI-related communications or just buffer
       the character streams, depending on the code written.  This
       might also work with the KXJ11 coprocessor.    

       Requires most, because it still needs the 5ma (maybe using
       idea in (1) above).  Also requires the most in coding support.
       Mostly thought of as a neat hack.

    Other ideas?

T.R	Title	User	Personal Name	Date	Lines
1813.1	Already out there somewhere.	DYO780::SCHAFER	Brad - back in Ohio.	`Wed Dec 14 1988 16:09`	11
	This topic has been discussed several times in previous conference topics. One fellow has ostensibly created his own sequencer and h/w interface for the PRO. Try the following: DIR/TITL={PDP,DEC,RS232} I'm sure something reasonable will show up. -b
1813.2		VAXRT::GENTRY	Megan Gentry MLO5-5/E76	`Wed Dec 14 1988 16:50`	9
	I have followed some of those notes, but most of them require more hardware hacking than I have the skill for, or require alteration of standard boards. I'm looking for something that I could unplug from a board on one machine and plug into a board on another machine. I'd like to see what ideas people have, and see if any further solutions may have been found.
1813.3	Hardware ain't the tough part	MENTOR::REG	Let's invent self referential image enhancing software	`Wed Dec 14 1988 17:29`	11
	I suppose one could just take whatever "serial line" port there is and plug a MIDI port adapter onto it ?? kinda like they do for Macs and Amigas. The "Challenging" part is to write a sequencer and all its little, make that BIG editing functions, IMHO. R
1813.4		SALSA::MOELLER	Richard Clayderman wannabe	`Wed Dec 14 1988 20:31`	3
	don't forget the opto-isolator in front of the UART. karl
1813.5	x32 clock	DFLAT::DICKSON	Plan data flows first	`Thu Dec 15 1988 09:19`	5
	And you have to get the clock-rate right. The Mac's built in serial port hardware is considerably more flexible than the stuff we put on our serial boards. Those MIDI adaptors for the Mac supply a 1MHz clock signal that the mac divides by 32 to run the port. If the DEC hardware you are using will not take an x32 external clock, you are out of luck.
1813.6	A bit overkill. Think simple.	LEDDEV::ROSS	shiver me timbres....	`Thu Dec 15 1988 10:54`	19
	The midi spec requires certain rise and fall times at the opto. You may or may not be able to get most 20ma converters tweaked to handle this, altho the 5ma is probably no problem. I have a design (actually, also layed-out boards) that just plugs into a DLVJ1 and is the midi interface you might be desiring... Ive used it with a 11-23 and 11-73. With RT11, you can even handle a full bandwith system exclusive dump of voice data real time to floppy..... send me some mail... RKNRON::ROSS ron
1813.7		VAXRT::GENTRY	Megan Gentry MLO5-5/E76	`Thu Dec 15 1988 12:31`	8
	RE: .4 > don't forget the opto-isolator in front of the UART. (Assuming above is regarding idea (2) from my base note). Is the isolator on the DRV-side or the MIDI-side of the UART?
1813.8		ANT::JANZEN	Tom LMO2/O23 296-5421	`Thu Dec 15 1988 12:56`	3
	the opto-isolator is on the midi side. it isolates systems and keep ground currents away so that they don't cause hum and crud etc. Tom
1813.9		SALSA::MOELLER	Richard Clayderman wannabe	`Fri Dec 16 1988 11:34`	8
	< Note 1813.6 by LEDDEV::ROSS "shiver me timbres...." > > I have a design (actually, also layed-out boards) that just > plugs into a DLVJ1 ........ Ive used it with a 11-23 and 11-73. Ronn.. would this work on a VAX using the KXJ11 board ? J11 processor, 512Kb memory, programmable (presumably DLVJ1-emulatable) ports...? karl,still trying to use his MVII creatively..