Oct SN76489 MIDI Array

The SN76489 is the same sound chip as found in the SEGA Master System. This is an array of eight SN76489 sound chips playable via USB MIDI, for a total of 32 hardware channels.

MIDI channels 1 - 16 are each split, so that each channel can represent two hardware channels. This is achieved by splitting the MIDI pitch range across two SN76489 channels. A C3 played on MIDI channel 1 with a transposition of -36 semitones will sound like a C3 being played on SN76489 chip 1, channel 1. A C3 played on MIDI channel 1 with a transposition of +24 semitones will sound like a C3 being played on SN76489 chip 1, channel 2. 

Thus, the 16 MIDI channels are mapped as follows: 

SN76489 Chip 1, Channel 1: MIDI Channel 1 -36 semitones

SN76489 Chip 1, Channel 2: MIDI Channel 1 +24 semitones

SN76489 Chip 1, Channel 3: MIDI Channel 2 -36 semitones

SN76489 Chip 1, Channel 4: MIDI Channel 2 +24 semitones

SN76489 Chip 2, Channel 1: MIDI Channel 3 -36 semitones

SN76489 Chip 2, Channel 2: MIDI Channel 3 +24 semitones

SN76489 Chip 2, Channel 3: MIDI Channel 4 -36 semitones

SN76489 Chip 2, Channel 4: MIDI Channel 4 +24 semitones

SN76489 Chip 3, Channel 1: MIDI Channel 5 -36 semitones

SN76489 Chip 3, Channel 2: MIDI Channel 5 +24 semitones

SN76489 Chip 3, Channel 3: MIDI Channel 6 -36 semitones

SN76489 Chip 3, Channel 4: MIDI Channel 6 +24 semitones

SN76489 Chip 4, Channel 1: MIDI Channel 7 -36 semitones

SN76489 Chip 4, Channel 2: MIDI Channel 7 +24 semitones

SN76489 Chip 4, Channel 3: MIDI Channel 8 -36 semitones

SN76489 Chip 4, Channel 4: MIDI Channel 8 +24 semitones

SN76489 Chip 5, Channel 1: MIDI Channel 9 -36 semitones

SN76489 Chip 5, Channel 2: MIDI Channel 9 +24 semitones

SN76489 Chip 5, Channel 3: MIDI Channel 10 -36 semitones

SN76489 Chip 5, Channel 4: MIDI Channel 10 +24 semitones

SN76489 Chip 6, Channel 1: MIDI Channel 11 -36 semitones

SN76489 Chip 6, Channel 2: MIDI Channel 11 +24 semitones

SN76489 Chip 6, Channel 3: MIDI Channel 12 -36 semitones

SN76489 Chip 6, Channel 4: MIDI Channel 12 +24 semitones

SN76489 Chip 7, Channel 1: MIDI Channel 13 -36 semitones

SN76489 Chip 7, Channel 2: MIDI Channel 13 +24 semitones

SN76489 Chip 7, Channel 3: MIDI Channel 14 -36 semitones

SN76489 Chip 7, Channel 4: MIDI Channel 14 +24 semitones

SN76489 Chip 8, Channel 1: MIDI Channel 15 -36 semitones

SN76489 Chip 8, Channel 2: MIDI Channel 15 +24 semitones

SN76489 Chip 8, Channel 3: MIDI Channel 16 -36 semitones

SN76489 Chip 8, Channel 4: MIDI Channel 16 +24 semitones

The hardware setup has one Teensy LC, with a common data bus (digital pins 0 - 7) and individual chip select (digital pins 8 - 15). One external 4 MHz crystal provides the timing for all eight SN76489.

Download the code here: http://milkcrate.com.au/_other/downloads/arduino/oct_sn76489.ino