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

TRUE     EQU  0FFH
FALSE    EQU  0

DISP_BIT EQU  01
EXIT_KEY EQU  10000000B   ; K8

DATA SEGMENT
MESG       DB 'PLEASE PRESS ANY KEY',0DH,0AH,'$'
SEG7CODE   DB 0C0H,0F9H,0A4H,0B0H,99H,92H,82H,0F8H,80H,98H
           DB 88H,83H,0C6H,0A1H,86H,8EH
DISP_BUF   DB 0
EXIT_FLAG  DB 0

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
NEXT:   CALL KEYINPUT
        CALL DISP
        CALL TEST_EXIT_KEY
        CMP EXIT_FLAG,TRUE
        JNZ NEXT
        MOV AH,4CH
        INT 21H

KEYINPUT:
              MOV AH,0BH
              INT 21H
              CMP AL,0FFH
              JNZ KEYINPUT_RET
                  MOV AH,1
                  INT 21H
                  INC DISP_BUF
KEYINPUT_RET: RET

TEST_EXIT_KEY:
                   MOV DX,PORT_C
                   IN AL,DX
                   TEST AL,EXIT_KEY
                   JZ TEST_EXIT_KEY_RET
                      MOV EXIT_FLAG,TRUE
TEST_EXIT_KEY_RET: RET

; INPUT: DISP_BUF
DISP:
        LEA BX,SEG7CODE
        MOV AL,DISP_BUF
        AND AL,0FH
        XLAT
        MOV DX,PORT_B
        OUT DX,AL
        MOV AL,DISP_BIT
        MOV DX,PORT_A
        OUT DX,AL
        RET

CODE    ENDS
        END START