实验17_8250串行通讯实验.asm

8250串行通讯实验：键盘输入一个字符

;**************************
;*     8250串行通信       *
;**************************
DATA SEGMENT
PORT        equ 2b8h
PORT1        equ 2b9h
PORT3        equ 2bbh
PORT5        equ 2bdh
MES    DB 'You can play a key on the Keyboard!',0AH,0DH
    DB 'ESC quit to dos!',0AH,0DH,'$'
DATA ENDS

CODE SEGMENT
    ASSUME CS:CODE,DS:DATA
START:        MOV    AX,DATA
        MOV    DS,AX
        MOV    AL,80H
        MOV    DX,PORT3
        OUT    DX,AL
        MOV    AL,13                ;set light divisor
        MOV    DX,PORT
        OUT    DX,AL
        MOV    AL,00                ;set low divisor 9600 boud
        MOV    DX,PORT1
        OUT    DX,AL
        MOV    AL,00011011B         ;8 bits 1 stop 
        MOV    DX,PORT3
        OUT    DX,AL
        MOV    AL,00H
        MOV    DX,PORT1
        OUT    DX,AL                ;interrupt enable all off
        MOV    DX,OFFSET MES
        MOV    AH,09H
        INT    21H
WAITI:        MOV    DX,PORT5
        IN     AL,DX                ;GET LINE STATUS
        AND    AL,20H
        TEST    AL,20H
        JZ    WAITI
        MOV    AH,01
        INT    21H
        CMP    AL,27
        JZ    EXIT
        MOV    DX,PORT
        INC    AL
        OUT    DX,AL
        MOV    CX,40H
S50:        LOOP    S50
NEXT:        MOV    DX,PORT5
        IN    AL,DX
        AND    AL,01
        TEST    AL,01
        JZ    NEXT
        MOV    DX,PORT
        IN     AL,DX
        MOV    DL,AL
        MOV    AH,02
        INT    21H
        JMP    WAITI
EXIT:        MOV    AH,4CH
        INT    21H
CODE ENDS
END START