Dermot,

...when I try to input the digital data all I get is rubbish

How do you watch data received by port1? I couldn't find your way(:-).

Seems to me you have to output data via another port, for instance, port2. So change the program as showed below and compare values on both ports.

$MOD812
       ORG  0000H
       LJMP START

       ORG  0200H
START: MOV  SP,#40H
       MOV  P1,#00H   ;Makes port 1 an i/p
AGAIN: MOV  A,P1      ;input data into Acc
       MOV  P2,A      ;output data to port2
       JMP  AGAIN
       END

Regards,
George