mov dptr,#0nnmmh
movx a,@dptr

I recommend nn=0, but that may not matter. The above will set P2 to nn, latch mm in the data latch, then input the data lines to the acc.
mov @dptr,a
will do the same except output the data lines


Make sure P0 has resistor pull-ups and it is a good idea to make sure that NO moves to P0 or P2 - exept by memory read/write - takes place anywhere. Some brands and derivatives have a problem setting address and data when port pins are held low.

Have fun,

Erik