南邮微机实验 串行口的测试(查询发送，中断接收)

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DATA SEGMENT USE16
MESG DB 'HELLO'
LENS EQU $-MESG
OLD0B DD ?
DATA ENDS
CODE SEGMENT USE16
ASSUME CS:CODE,DS:DATA
BEG:   MOV AX,DATA
MOV DS,AX
CLI                        ;关中断
CALL I8250
CALL I8259
CALL RD0B                  ;读中断向量
CALL WR0B 				  ;写中断向量
STI                        ;开中断

MOV BX,OFFSET MESG
MOV CX,LENS

SCANT: MOV DX,2FDH
IN AL,DX
TEST AL,20H
JZ SCANT

MOV DX,2F8H
MOV AL,[BX]
OUT DX,AL
INC BX
MOV EDX,0
SINEXT:DEC EDX
JNZ SINEXT
LOOP SCANT

RETURN:CALL RESET
MOV AH,4CH
INT 21H

RECEIVE PROC
PUSH AX
PUSH DX
PUSH DS
MOV AX,DATA
MOV DS,AX
MOV DX,2F8H
IN AL,DX
AND AL,7FH
MOV AH,2
MOV DL,AL
INT 21H
JMP EXIT
EXIT:  MOV AL,20H      ;中断结束命令
OUT 20H,AL
POP DS
POP DX
POP AX
IRET
RECEIVE ENDP

I8250 PROC
MOV DX,2FBH
MOV AL,80H
OUT DX,AL
MOV DX,2F9H
MOV AL,0
OUT DX,AL
MOV DX,2F8H
MOV AL,60H
OUT DX,AL
MOV DX,2FBH
MOV AL,03H
OUT DX,AL
MOV DX,2F9H
MOV AL,01H
OUT DX,AL
MOV DX,2FCH
MOV AL,08H
OUT DX,AL
RET
I8250 ENDP

I8259 PROC
IN AL,21H
AND AL,11101111B
OUT 21H,AL
RET
I8259 ENDP

RD0B PROC
MOV AX,350CH
INT 21H
MOV WORD PTR OLD0B,BX
MOV WORD PTR OLD0B+2,ES
RET
RD0B ENDP

WR0B PROC
PUSH DS
MOV AX,CODE
MOV DS,AX
MOV DX,OFFSET RECEIVE
MOV AX,250CH
INT 21H
POP DS
RET
WR0B ENDP

RESET PROC
IN AL,21H
OR AL,00010000B
OUT 21H,AL
MOV AX,250CH
MOV DX,WORD PTR OLD0B
MOV DS,WORD PTR OLD0B+2
INT 21H
RET
RESET ENDP
CODE ENDS
END BEG