bits

.MODEL  SMALL   ; use memory model
.STACK  100H    ; reserves 100h bytes for stack
.CODE           ; starts code segment

START:
    MOV    DX, 379H    ; select status port of LPT1
    IN     AX, DX      ; read input X from status port of LPT1
    MOV    AH, 00H     ; neglect higher bytes of AX since LP1 is 8bit
    MOV    BX,AX
    MOV    CX,256      ; CX=256
    SUB    CX,BX       ; CX=256-X
    MOV    AX,00H      ; set initial value 0 for count

COUNTUP:
        MOV     DX,378H    ; select data port of LPT1
        OUT     DX,AX      ; write value in AX to DATA port
        CMP     AX,CX      ; compare  current count value with CX
        JZ      DONE       ; if AX and CX equal goto DONE
        INC     AX         ; else keep incrementing AX
        JUMP    COUNTUP    ; loop again counter

DONE:
    MOV AH, 4CH    ; turminate programe with exit code of ( 256-X )
    INT     21H    ; Call the interrupt to exit

END START