Like this:

   mov   P2,#0FFh
   mov   R0,#0Ch   ;for PORT A  8255 #1
   movx  @R0,A

If you will use MOVX @Ri only for 8255 access (upper address = 0FFh) and for all other external memory accesses you use MOVX @DPTR, you need to load P2 with 0FFh only once (in fact, you don't need to load it at all, as 0FFh is the default reset state...)

Jan Waclawek