1978 was very early in the 'personal computer' era. I'd guess that the use of a VCO was modeled after early synthesizers like the Moog. (It used a 1-volt per oc

1978 was very early in the 'personal computer' era. I'd guess that the use of a VCO was modeled after early synthesizers like the Moog. (It used a 1-volt per octave scheme ... changing the external voltage input from 2 to 3 volts moved pitch up an octave.) The 76477 could take an external voltage (up to 5v) (Pin 16 via J2) for pitch - maybe the design's intent was to be able, when needed, to inexpensively generate external voltages, e.g. through a pot. The much-more powerful General Instrument AY-3-8910 arriving in 1978 sank any hopes the 76477 had. https://en.wikipedia.org/wiki/General_Instrument_AY-3-8910 https://en.wikipedia.org/wiki/General_Instrument_AY-3-8910