DATA  SEGMENT
        DATA  ENDS
        CODE  SEGMENT
              ASSUME    DS:DATA,CS:CODE
      START:  PUSH      DS
              SUB       AX,AX
              MOV       AX,DATA
              MOV       DS,AX

       ; MODE  EQU       89H
      ; PORTA  EQU       288H
       ;PORTC  EQU       28AH
       ;CNTRL  EQU       28BH

              MOV       DX,28BH
              MOV       AL,89H
              OUT       DX,AL

        LOP:  MOV       DX,28AH
              IN        AL,DX
              MOV       DX,288H
              OUT       DX,AL

              SUB       AL,AL
              MOV       AH,0BH
              INT       21H
              CMP       AL,00H
              JZ        LOP
              RET
        CODE  ENDS
              END       START