the point I was trying to make is keypad scanning routines read pins every ,15-30 ms, not microseconds

Hi Reza,
If your routine reads the keyboard every 15-30ms than its most likely that your key gets debounced during this period. If your routine considers a valid pressing only if found pressed in two consequetive routine calls then what exactly are you doing is software debouncing. Whats so special about it?

Regards,
Prahlad Purohit