I have recently developed and sold a digital lock application with 4 x5 keypad (20 keys).

So I can only give you a hint.

put 4 cols on four ports (say p0.0 ~p0.3) and put 4 rows on four remaing ports (say p0.4 ~p0.7).

Pullup every port.

turn one row low ( clr p0.4) and check all columns if any has gone low (jb p0.0,next).

Let my contract expire till my client has honored his order, I'll send you the whole code.

Good Luck

Babar/

Good luck