121 Programmable Hardware Manual (PHM)
© Tibbo Technology Inc.
Due to flexible scan and return line mapping provided by the keypad (kp.) object,
you can assign any combination of GPIO lines to connect to your keypad. Up to 8
scan and 8 return lines can be assigned. On the EM2001 board, all scan line must be
configured as outputs, and all return lines — as inputs.
To build a keypad you will need to have at least one return line. A sensible count of
scan lines, however, starts from two! Having a single scan line is like having no scan
lines whatsoever — you might just as well ground this single scan line, i.e. always
keep it active: