MPU-401 found without PC card

[Magnus Danielson]

> I think that I have found an interesting DIY project to be...
> It's a little grey metal box, about the size of a paperback book.
> The markings say "Roland Midi Processing Unit MPU-401", and it 
> has a 25 pin "To computer" connector, four DIN connectors, one marked
> MIDI IN, two marked MIDI OUT, one marked SYNC OUT, and three 1/4"
> jacks, marked TAPE IN, TAPE OUT, and METRONOME OUT.
>  
> As far as I can tell, it is half of an old IBM computer-to-MIDI
> interface (I am missing the ISA bus card that goes in the computer).

You are rigth, but the card in the PC is really nothing put a ISA bus decoder
and buffer card, just like those simple IDE cards... just as simple.

> I do not believe that the 25 pin D connector is a serial port.

No, it's not a serial port. Here is the pinout (since you seem to lack it):

Name	Pin	Direction
D0	1	I/O
D1	14	I/O
D2	2	I/O
D3	15	I/O
D4	3	I/O
D5	16	I/O
D6	4	I/O
D7	17	I/O
A0	5	I
A1	18	I
A2	6	I
RD*	9	I	Read Enable
WR*	22	I	Write Enable
CS*	10	I	Chip Select
DSR*	23	O	Interupt output
RES*	11	I	Reset
+5V	12 & 24	I
GND	13 & 25	I

There you are. All the * marked signals is inversed polarity. You can wire this
babe to basically any machine (haul out that old Commodore 64!) as long as you
wire it tidy to the bus as above. For a PC, wire the data lines througth a
transiever chip ('LS245) and let the other signals go thougth a buffer chip 
('LS244). The interupt shoud go througth a open-collector chip ('07) if I 
recall
rigth... Also make a CS generation cursuit out of a comparator chip to select
330 (but not the three lowest addresslines). Now, you can run your favorite
PC sequencer :) The IRQ is 9.

> These little boxes were made with enough processing power so that
> an old underpowered 8086 PC could act as a MIDI sequencer.

Rigth. There's several neat features in that controller.

> My question is, what can I do with this box without the PC card
> and the software (it didn't come with it... I probably got it cheap
> because it's *worthless* :-).  What do these 1/4" jacks do?
> Does anyone have any experience playing with these guys?

Since the PC card is such a small thing, you could spend some effort on 
building
one and you can use it with any MPU-401 supporting software. But even without
the PC card you can wire it to any machine since the power is in the box.

The 1/4" jacks are for sync input and output to tape, so that you can keep the 
sequencer in sync with the tape...

> At the very least, I would think that I could make some kind of
> MIDI-to-trigger or trigger-to-MIDI box out of it?  No?  Maybe
> even a MIDI-to-CV?  Or do I have to gut the box and put my own
> electronics inside? :-(

This box is the mind of it... so don't you carve it empty...
With not too much of external CPU would easilly be able to let it do MIDI->CV
tricks...

I even have code for interprenting and sending commands to this baby.

Cheers,
Magnus