; CHECK-SUM PROGRAM TEST
        LDR     R0,=ROM_ADDRESS     ; pointer to data ROM
        LDR     R2,=ROM_SIZE        ; data size
        MOV     R1,#0               ; R1 is used to hold the sum
        ; add the words including the check-sum word
OVER    LDR     R3,[R0]             ; load the word 
        ADD     R1,R3               ; add the word
        ADD     R0,R0,#4            ; point to next one
        SUBS    R2,R2,#1            ; decrement counter
        BNE     OVER                ; until all is done
        ; test it
        TST     R1,R1               ; see if the sum is zero
        BEQ     NO_ER               ; if it is, go display the message
        ; display the message for error
        B       .                   ; stay here

NO_ER 
        ;display the message for no error