MOV DX,303H 
  MOV AL,80H 
  OUT DX,AL
AGAIN: MOV DX,300H
  MOV AL,55H
  OUT DX,AL
  CALL QSDELAY 
  MOV AL,0AAH 
  OUT DX,AL
  CALL QSDELAY
  MOV AH,01
  INT 16H 
  JZ AGAIN 
  MOV AH,4CH
  INT 21H 
  QSDELAY PROC NEAR
  MOV CX,16572 
  PUSH AX
W1: IN AL,61H
  AND AL,00010000B
  CMP AL,AH
  JE W1
  MOV AH,AL
  LOOP W1
  POP AX
  RET
  QSDELAY ENDP