Positivo in Negativo e viceversa

*Trasformare un numero positivo in negativo e viceversa
        ORG     $8000
SUBR    MOVE.W  VAL,D0
        NOT.W   D0
        ADD.W   #1,D0
        MOVE.W  D0,RES
        RTS

SUBR2   MOVE.W  VAL2,D0
        NOT.W   D0
        ADD.W   #1,D0
        MOVE.W  D0,RES2
        RTS

START:  MOVEM.L D0,-(SP)
        JSR SUBR
        MOVEM.L (SP)+,D0
        MOVEM.L D0,-(SP)
        JSR SUBR2
        MOVEM.L (SP)+,D0

        SIMHALT
        ORG     $8400
VAL     DC.W    5
VAL2    DC.W    -5
RES     DS.W    1
RES2    DS.W    1
        END     START