Hi Peter

Here is the assembler code:

FindRow:
mov a,P1 ;read rows
mov r0,#4 ;initialize counter

TryNextRow:
rrc a ;read next row
jnc Rowfound
djnz r0,TryNextRow

RowFound:
mov a,#4 ;number of rows
subb a,r0 ;compute row number - note C=0
clr C
ret

I hope this this is enough to help you? Remember Port1 is connected to a 4x4 matrix type keypad.

Regards,
KY