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Last modified on 21 February 2021, at 17:59

MIDI

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Musical Instrument Digital Interface (MIDI)

Software Protocol

Basically transmits commands like key on, key off, plus pitch/volume parameters.

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Hardware Protocol

The data is transferred at 31250 bits per second, using 8-N-1 format (one start bit, eight data bits, no parity bit, and one stop bit). So far, the MIDI protocol is much similar to RS232, and many MIDI interfaces do actually use standard "RS232" UART chips. Differences to RS232 are:

  • The signals are transmitted as TTL levels (0V and 5V) (unlike +/-12V on RS232) with 5V reference voltage (unlike 0V on RS232)
  • The receiver should pass the TTL signal through an Opto-Isolator
  • The 31250 Hz baudrate isn't a standard RS232 rate
  • MIDI is one-directional (MIDI OUT implements only TX, no RX, and MIDI IN implements only RX, no TX)
  • There are no control signals like CTS/RTS/DSR/DTR used

Schematic

MidiElectricalSpecificationDiagram.gif

MIDI Interfaces for the CPC

MIDI software for the CPC

Presentation in ACU magazine

Presentation in CPCAI magazine

DIY MIDI Interface from CPCAI


Weblinks