The board is just a 4067 analog MUX to scan the frontpanel pots for synth parameters and send them over to the DSP by TTL-MIDI..
It can also scan a keyboard, pitch-bend and trig/CV inputs for the synth.
Keeping track of presets in it's EEPROM, run Arpeggios etc.
The DSP runs an analog model of a synth, reading the parameters over TTL-MIDI on one pin and outputs the audio on another pin.