General Instruments Capacitive Keyboard Encoder

Bingo. That's basically my circuit here (pin for pin) with minor differences in RC values and a much more interesting serial interface (and a _four_ finger salute no less! N-S-T-V Take that DOS ...), although mine supports a buzzer/speaker. The principal inconsistency is that pin 25 is marked "CS" and left open in the "binder 1" schematic (page 132 of 134), and then doesn't appear in your hand-drawn schematic (page 7 of 24). In my circuit it's wired to the 8039 ~PSEN. The straight-thru wiring on ~RD and ~WR alongside ALE with no address decoding is IMO rather odd. I wonder how that design actually works (either assumes that it is the only writable device present, or actually latches 8 bits of address and shadows some valid ROM address) and then what gets written to the encoder for what purpos(es). Disassembly of the EPROM should answer those questions. My objective here is to replace the bit-banged interface with a parallel interface emulating one for an Intel MDS-230. Two questions on notation.: 1. In the "binder 1" schematic pin 6 is marked as R<sub>y and is pulled up via resistor to +5v. On your hand-drawn schematic the corresponding pin appears to be labeled "PVR". What might be the function of this pin? 2. In the "binder 1" schematic pin 15 is marked as C<sub>m and is attached to an RC circuit. On your hand-drawn schematic the corresponding pin appears to be labeled "RC". C = 100 nF. What might be the function of this pin? I'm guessing ~(Power On Reset) rather than as the basis for an on-chip oscillator as seen in the AY-3-4592 pin 36 "RC" given the relatively high capacitance value. Thank you for these new breadcrumbs. paul