Awesome custom MIDI controller beast
61 trigger switches (37 keys, 24 drums) were connected via this custom Commodore 64 parallel port interface. The port's 8 data lines were configured as 4 outs and 4 ins (8 bits). The 4 outs selected one of 4 '1 of 16 multiplexers', each capable of scanning up to 16 triggers (a maximum of 64). The 4 ins (4 bits = 16 triggers) returned data from these multiplexers. The board is shown here without the multiplexer chips.
Custom designed software on the C64 performed MIDI routing to as many as 16 different MIDI devices (percussion and synth). Each switch was scanned in succession by a looping machine code routine. Because of the design, no two switches could be triggered at exactly the same time, but the system ran fast enough that this was rarely a problem. At any time, triggers could be re-routed to a different MIDI device and/or sound. Routing patches could be created and saved on the computer. Loading of patches could be initiated from any of the Hammon d'Eggs triggers. The unit supported up to four sticks simultaneously.