Looking for help with a 8051 and assembly

if i want to add inputs on P1 with P2 and output on P2 is that possible? tried simulating but doesnt operate as expected. It works if i use p3 as 2nd input then output on p2.
MOV A, P1
MOV B, P3
ADD A, B
MOV R0, A
MOV P2.1, C
MOV 0A0H, R0
END