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MIDI is short for Musical Instument Digital Interface.
The hardware consist of a 31.25 kb/s asynchronous link using a start bit,
8 data bits and a stop bit. The link itself is a current loop type on which
the logical 0 is formed by current on. The receiver side must be opto-
coupled using a device that requires less than 5 mA to turn on and have
rise and fall times of less than 2 .s. The connectors on the devices must
be female 5-pin DIN (180.), pin 1 and 3 are not connected, pin 2 is
connected to ground at the transmitting side, pin 4 and 5 are the current
loop. The cable should not exceed 50 feet and is a shielded twisted pair
cable.
Input: (MIDI IN)
/---\ +--------+ +-----------------+
4 --------------|------| 220 . |----------------+---+ |
| | +--------+ | | | |
| | - | . . |
| | . | - . |
| | | | | |
5 --------------|--------------------------------+---+ |
\-+-/ +-----------------+
|
Shield
Output: (MIDI OUT & MIDI THRU)
5V
| +--------+ /---\
+-----------------| 220 . |--------------|---- 4
+--------+ | |
| |
| |---- 2
|\ |\ | |
| \ | \ +--------+ | |
-------| >O----------| >O---------| 220 . |------------------- 5
| / | / +--------+ \-+-/
|/ |/ |
Shield
(Output of the optocoupler is directly connected to TTL-IC driving the
MIDI-THRU output!)
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