Simple MIDI?

Mikko Helin MHELIN at tne01.tele.nokia.fi
Wed Jan 21 15:11:08 CET 1998


>Some year ago I posted a schematic of a thing with a 6850 and a couple of
>hex inverters that sent program change status and data. It went to the
>music machine archives at hyperreal but I don't know if it's still there or
>not. The problems is, I haven't seen a 6850 or seen one for sale in a long
>time.

No schematics there, just a text file:

http://www.hyperreal.org/music/machines/categories/DIY/chips/6850

Data sheets of MC6850 can not be found at Motorolas www-site,
but they have the MFax system for ordering data sheet (you'll need 
the fax).

Use the page http://www.semi.harris.com/search.htm to search for 6402
data sheets. It seems to be still in production. An example of the use of
6402 can be found here:
http://www.hyperreal.org/music/machines/categories/DIY/schematics/MIDI_to_DIN_sync/new_mididin.gif

Other 6402 chips are AY-3-1015 and COM8017, Harris part is CDP6402.

I have a future PC MIDI interface project (when I've got my Telecaster
ready,  built the tube combo amp for it, built an external ADC & DAC
for AudioPCI of CS4222 and built a case for all analog modules and
midi2cv converter) where I'm going to use IDT7402 1 kB FIFOs and
COM8017's (6850's could do as well if they are available) for
multi-port parallel port MIDI interface. I don't like any MIDI
interfaces  that connect to serial port or doesn't have large enough
FIFOs, as they kill the timing when they wait for ready-to-send status
in status polling loooop. So if there's a large FIFO, just a single
"out dx,al" instruction is what is needed, assuming sys-ex data size
doesn't exceed that 1 kB (there are pincompatible 8 kB versions of the
same FIFO's that can be used instead).


---
Mikko




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