KCOD_0 DB 0,1,2,3 
  KCOD_1 DB 4,5,6,7 
  KCOD_2 DB 8,9,0AH,0BH 
  KCOD_3 DB 0CH,0DH,0EH,0FH 
  PUSH BX 
  SUB AL,AL 
  OUT PORT_A,AL
K1: IN AL,PORT_B 
  AND AL,00001111B 
  CMP AL,00001111B 
  JNE K1 
  CALL DELAY 
K2: IN AL,PORT_B 
  AND AL,00001111B 
  CMP AL,00001111B 
  JE K2 
  CALL DELAY 
  IN AL,PORT_B 
  AND AL,00001111B 
  CMP AL,00001111B 
  JE K2 
  key
  MOV AL,11111110B 
  OUT PORT_A,AL
  IN AL,PORT_B 
  AND AL,00001111B 
  CMP AL,00001111B 
  JE RO_1 
  MOV BX,OFFSET KCOD_0 
  JMP FIND_IT 
RO_1: MOV AL,11111101B 
  OUT PORT_A,AL
  IN AL,PORT_B 
  AND AL,00001111B 
  CMP AL,00001111B 
  JE RO_2 
  MOV BX,OFFSET KCOD_1 
  JMP FIND_IT 
RO_2: MOV AL,11111011B 
  OUT PORT_A,AL
  IN AL,PORT_B 
  AND AL,00001111B 
  CMP AL,00001111B 
  JE RO_3 
  MOV BX,OFFSET KCOD_2 
  keys
  JMP FIND_IT 
RO_3: MOV AL,11110111B 
  OUT PORT_A,AL
  IN AL,PORT_B 
  AND AL,00001111B 
  CMP AL,00001111B 
  JE K2 
  MOV BX,OFFSET KCOD_3 
  keys
FIND_IT:RCR AL,1 
  JNC MATCH 
  INC BX 
  JMP FIND_IT 
MATCH: MOV AL,[BX] 
  POP BX 
  RET