Solder side;
2 2
4 * 5 5 o 4
* * o o
1 * * 3 3 o o 1
180 degree Din Male 180 degree Din Female
Pin side;
2 2
5 * 4 4 o 5
* * o o
3 * * 1 1 o o 3
Midi uses a 180 degree 5 pin Din plug. The cable is a shielded twisted pair. The shield is connected to pin 2 (the top pin) at both ends of the cable. The cable uses male plugs at both ends. The female has pin 2 to ground at the sending side, not at the receiving side. This is done to avoid ground loops.
1 nc 2 GND 3 nc 4 Midi 5 Midi
Pin 4 of a female 180 degree Din plug is connected to + 5 Volt via a 220 Ω
resistor.
Pin 5 is connected via a 220 Ω resistor to;
+ 5 V for a logical 1
0 V for a logical 0
+-----+
+ 5 V >------+ 220 +--> Din Pin 4
+-----+
+-----+
Midi data >--+ 220 +--> Din Pin 5
+-----+
GND >-----------------> Din Pin 2
The LED part of an opto coupler is connected to pin 4 and 5 in series with a 220 Ω resistor;
+5V
\ /
|
+++
| |
+++
|
+-----+ *---> Midi data
Din Pin 4 >--+ 220 +---*-----+ |
+-----+ | | | /
--+-- --+-- |/
/|\ \|/ -> | Opto coupler
--+-- --+-- -> |\
| | |_\|
Din Pin 5 >------------*-----+ |
|
\|/
GND
This means that during a logical '0' a current of ca 5 mA runs through the cable. A disconnected cable signals a continuous '1', which means no data whatsoever.
Most RS232 buffers (1488, 1489) can cope with -15 ... 15 V
PC's use + / - 12 V, most modems + / - 8 V
They consider > 1 V On or '0' and < 1 V Off or '1'
Typical input impedance is 4k7
These use two opposite polarised signals called A and B.
+---+ +-
A | | |
+ +---+
+ +---+
B | | |
+---+ +-
+ +---+ < 2 ... 6 V
| | |
A - B | | |
| | |
+---+ +- < -2 ... -6 V
A - B > 300 mv (US 200 mv) is ON or '0'
A - B < -300 mv (US -200 mv) is OFF or '1'
The Common Mode Voltage ((A + B) / 2) is -7 ... 12 V, so you can drive a
line from a single 5 V source.
The line is terminated with 100 Ω.
RS 422 Buffers (75172, 75173) can be used for most balanced interfaces.
The European version (300 instead of 200 mv) is often referred to as V11 or
X27.
V35 drives + / - .55 V into a 100 Ω load.
The CMV is 0.