[sdiy] How to add MIDI IN to an old Casiotone 101

[Jack Jackson]

I have this old board, it's provides quite basic digital sounds from an NEC D990G chip. As far as I can tell, this chip also performs the matrix scanning of the keybed.

So if one were to add MIDI to it, this is how I envisage it:

1. MIDI note-on message received 
2. Microcontroller interprets note and uses a look-up table to tell it which position of the matrix this note fits.
3. Microcontroller waits until the switch for the notes row goes high
4. Microcontroller sends the correct pin high for that note.
5. Pin stays high until note-off is received.

So the micro would have to sync (or at least follow) the onboard chips scanning and just output the 5v for that note at the correct time.