We've told you where the problem is - but you haven't attended to it. I'm sure if you put your code through a simulator, you'd see exactly where your problem is.

Try this for some hints. The delay should be a few 10's of microseconds.

Do you have pullup resistors on P1.0..3? If so, what value.

[pre]
ROW1 .equ efh
ROW2 .equ dfh
ROW3 .equ bfh
ROW4 .equ 7fh

scan_keypad:
mov R2,#0 ;keys 0..3
mov P1,ROW1 ;select row 1
acall delay ;wait for things to settle
mov a,P1
anl a,#0fh ;columns only
jnz test_column
mov R2,#4 ;keys 4..7
mov P1,ROW2 ;select row 2
acall delay ;wait for things to settle
mov a,P1
anl a,#0fh ;columns only
jnz test_column
mov R2,#8 ;keys 8..11
mov P1,ROW3 ;select row 3
acall delay ;wait for things to settle
mov a,P1
anl a,#0fh ;columns only
jnz test_column
mov R2,#12 ;keys 12..15
mov P1,ROW4 ;select row 4
acall delay ;wait for things to settle
mov a,P1
anl a,#0fh ;columns only
jnz test_column
mov a,#NO_KEY ;no key was pressed
ret
[/pre]