The original prototype was designed using the PIC16F628, but the code shown below can easily be modified to work on any PIC with sufficient I/O capacity for the keypad interface, and the two lines required for the serial output-pin, and baud-rate selection pin.
CMCON is the comparator mode selection register. Loading a value of 7 into CMCON sets-up the PortA I/O-pins as digital, while turning OFF the comparators.
If you prefer to use another PIC that has A/D on PortA, simply replace CMCON = 7 with ADCON1 = 7 to turn OFF the A/D peripheral, and set PortA to digital.
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