Dear all,
I was going through the 4*4 matrix keypad interface with 8051 and was not quite comfortable with one thing.

Detection of switch press!

The code given in the text 'for scanning and identifying the key that is pressed' takes the switch press as 'continuously pressed' (a delay of 20msec is produced after switch press for debounce) and identifies the correct location(row,column) by setting each row zero and comparing with the column value.

So my doubt is, how would this comparison work? since the switch press would only produce a trigger pulse at the port but not a constant low level.
It would be nice if i could get few suggestions on this.

Thanking you,
Suresh.