MIDI (Musical Instrument Digital Interface)

Advantages of MIDI:

It's a standard
It's extensible
It works (within its limits)
Do we have something better yet?

Disadvantages of MIDI:

Bandwidth (Max 1.5 KHz updates)
Maximum cable length (15 meters)
No synchronous events
Message scheme based on keyboard model

MIDI Electrical Standard:

MIDI input uses an opto-isolated current loop.
MIDI output is just a buffer and some resistors.
MIDI thru is a buffered pass-through of the MIDI input signal.

MIDI Transmission Standard:

MIDI is transmitted as asynchronous bytes at 31250 bits per second.
One start bit, eight data bits, and one stop bit result in a maximum transmission rate of 3125 bytes per second.
If first bit = 1, the following byte is a "status" byte.
If first bit = 0, the following byte is a "data" byte.
The status byte determines the length of most messages, which are usually one, two, or three bytes in length.
System exclusive messages are of variable length and have a start and ending status byte.
More MIDI documentation

MIDI Output from the BASIC Stamp:

MIDI is a "serial" transmission standard.

On the BASIC Stamp, we use the SEROUT command:

'{ $STAMP BS2 }

baudmode      CON  60     '60 for BS2sx, 12 for BS2
midinoteon    CON  144    'MIDI note on status byte (for channel = 0)
midinoteoff   CON  128
midichannel   CON  0

SEROUT 15, baudmode, 0, [midinoteon+midichannel, 60, 64]  'output on pin 15

PAUSE 500                                           'pause for 500 milliseconds

SEROUT 15, baudmode, 0, [midinoteoff+midichannel, 60, 64]
END

IMPORTANT: The baudmode argument of the SEROUT command is dependent on the clock speed of the BASIC Stamp. For MIDI, baudmode = 60 when using a BS2sx and baudmode = 12 when using a BS2.