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The MIDI Forum

  Tuesday, 17 January 2023
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I have a Midi module in front of me containing a 5 pin DIN connector with 1-blue, 2-yellow,5-red connected. Do the colors being used obey in any way a given "standard"?

And from my understanding, Midi is RS232, 31250 Baud, right? Is there a cheap way, to retrieve a TTL level from it? Using a diode and a resistor or so?
Christoph set the type of the post as  Technical Question — 2 weeks ago
2 weeks ago
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#17311
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As far as I know, MIDI uses 3 pins ONLY of the 5 pin 180 degree DIN plug, the other two pins (#4 and #5) are not used. The wire connector colours are not relevant in any way, so could be anything. Pin 1 at one end is connected to pin one at the other, 2 to 2 and 3 to 3. A MIDI cable can be connected either way around, there should be no difference. A cable using pin 5 as you describe might relate to some special purpose, but would be somewhat hit-and-miss for normal midi use, i.e. it might work for some things but not for others.

MIDI is RS232, but the Baud Rate is different to those used for normal serial comms work. Most normal comms equipment does not support the MIDI rate.

Never heard of anything checking the TTL value, I believe that MIDI will still work normally over a wide range of signal strengths.

Geoff
2 weeks ago
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#17312
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Thanks. I believe my question about TTL level was silly. RS232 is between positive and negative levels and one might kill a TTL input
even with the negative level clamped to -0.7V (by a diode).
MIDI is a current loop. At the transmitter, pin 4 is connected to power, and pin 5 is switched to ground to make current flow. At the receiver, the optocoupler's LED is connected between pins 4 and 5. Both devices have resistors to limit the current to 5 mA.

To detect the signal cheaply, connect a pull-up resistor to pin 5, and measure the voltage at pin 5. You get a plain UART signal.
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