8051 Assembly 8 bit Address Based Subtraction program

                ORG 0000H

                MOV DPTR, #0030H

                MOVX A, @DPTR

                MOV R0, A

                INC DPTR

                MOVX A, @DPTR

                SUBB A, R0

                MOV DPTR, #0090H

                MOVX @DPTR, A

                MOV PCON, #02H