Assuming he wants it to count on P0 from 0000-1001 in binary,
this program could do it. Since he is only counting to 1001,
he could use a 9 MOV lines with a jmp to a delay in between them. I'm also sure this is a sloppy way to do this, as some of you don't like to use registers for variables, but I always found it to simplify things, provided you keep track of all of
the one's you use.

MOV A, #0 ; Use A as your variable
MOV R0, #9 ; Set R0 to use as your loop, loop 9 times

COUNTDOWNLOOP: ; Beginning of your loop
MOV P0, A ; Outputs on Port 0 the value of Acc
ADD A, 1 ; Adds 1 to Acc for next loop

timedelay: ; Time delay loop
MOV R1, #50 ; These two values set your time delay, increase them for more delay
MOV R2, #250
loop:
djnz r1, loop
djnz r2, loop


DJNZ R0, COUNTDOWNLOOP ; Subtract 1 from R0, and loop if its not 0
; Once zero, the program passes this line and ends.

END