The circuit is based in part on the Roland SH-101 / System100m design with several enhancements.
Manual GATE buttons
Three timing ranges: (1 second, 10second, 1minute A/D times)
Normal and inverted outputs
End of Decay (EOD) logic output
Cycle mode (which GATE logic control)
Retrig input (allows re-triggering of the envelope if source gate held high)
Dynamic control of the envelope output level (each ADSR is routed through a linear VCA and the control is normalled to +5V via the LEVEL jack. You can patch another control source like an LFO or VELOCITY level from a keyboard to this jack.