Hi Peter,

you must decide, want you to use P0 as normal port (MOV P0,#0FFh) or to access external memory (MOVX A,@DPTR).
Only one of these can be done, both together was useless.

On MOVX A,@DPTR you see short the low address (DPL) on P0 and after this it goes to high impedance, because you read from an external memory.


Peter