PORT_A   EQU  208H
PORT_B   EQU  209H
PORT_C   EQU  20AH
PORT_CW  EQU  20BH

EXIT_KEY EQU  00000100B   ; K8

DATA SEGMENT
MESG       DB 'PLEASE PRESS ANY KEY',0DH,0AH,'$'
KEY_BUF    DB 11,?, 10 DUP(?)
DATA ENDS

CODE SEGMENT
        ASSUME CS:CODE,DS:DATA
START:  MOV AX,DATA
        MOV DS,AX
        MOV DX,PORT_CW
        MOV AL,89H
        OUT DX,AL
        LEA DX,MESG
        MOV AH,9
        INT 21H
        LEA DX,KEY_BUF
        MOV AH,0AH
        INT 21H
        CALL CHG
        LEA SI,KEY_BUF
        ADD SI,12
        MOV AL,'$'
        MOV [SI],AL
        LEA DX,KEY_BUF
        ADD DX,2
        MOV AH,09H
        INT 21H
        CALL CHG
        CALL TEST_EXIT_KEY
        CALL DISP
        MOV AH,4CH
        INT 21H

DISP:
        MOV DX,PORT_A
        MOV AL,01010101B
        OUT DX,AL
        RET

CHG:
          LEA SI,KEY_BUF
          INC SI
          MOV CL,[SI]
          MOV CH,0
CHG_NEXT: INC SI
          MOV AL,[SI]
          OR AL,20H
          MOV [SI],AL
          LOOP CHG_NEXT
          RET



TEST_EXIT_KEY:
                   MOV DX,PORT_A
                   MOV AL,11111110B
                   OUT DX,AL
                   MOV DX,PORT_C
                   IN AL,DX
                   TEST AL,EXIT_KEY
                   JNZ TEST_EXIT_KEY
                   RET


CODE    ENDS
        END START