MOV DPL,#0FH
MOV DPH,#3AH
MOVX A,@DPTR
SWAP A //A VU
MOV R7,A //R7 VU
MOV A,P1
SWAP A
MOVX @DPTR,A //(3A0FH)= QPH
XCH A,R7 //A VU
MOV P1,P3 //P1 RS
MOV R1,#P1
XCHD A,@R1 //A VS P1 RU
MOV P3,A //P3 VS