example (no pullups)
C1 = p1.0
C2 = p1.1
C3 = p1.2
R1 = p1.3
R2 = p1.4
R3 = p1.5

send out to P1
038h (detect)
03eh (col1)
03dh (col2)
03bh (col3)

With these values on P1, one at the time, observe what happens to P1.3, p1.4 and p1.5 when various keys are pressed.

This tedious excersise will tell you more than 5 books about keypad theory.

Have fun,

Erik