8253a.asm

微机原理与接口技术的部分课后题（十几题经典的）程序

IOPORT		EQU 0C400H-0280H
IO8253A		EQU IOPORT+283H
IO8253B		EQU IOPORT+280H
CODE SEGMENT
	ASSUME  CS:CODE
START: MOV AL,10H       ;设置8253通道0为工作方式2,二进制计数
	 MOV DX,IO8253A
	 OUT DX,AL
	 MOV DX,IO8253B      ;送计数初值为05H
         MOV AL,05H
         OUT DX,AL
   LLL:  IN AL,DX         ;读计数初值
	 CALL DISP        ;调显示子程序
	 PUSH DX  
	 MOV AH,06H 
	 MOV DL,0FFH
	 INT 21H
	 POP DX
	 JZ LLL
	 MOV AH,4CH       ;退出
	 INT 21H
DISP   PROC NEAR        ;显示子程序
	 PUSH DX
	 AND AL,0FH       ;首先取低四位
	 MOV DL,AL
	 CMP DL,9         ;判断是否<=9
	 JLE  NUM         ;若是则为'0'-'9',ASCII码加30H
	 ADD DL,7         ;否则为'A'-'F',ASCII码加37H
NUM:     ADD DL,30H
	 MOV AH,02H       ;显示
	 INT 21H
        MOV   CX,9000  
 DE1:    MOV   DI,0FFF0H         ;DI赋初值5000
 DE0:    DEC   DI              ;减1计数
	JNZ   DE0                ;DI不为0
	LOOP  DE1
	 MOV DL,0DH       ;加回车符
	 INT 21H
	 MOV DL,0AH       ;加换行符
	 INT 21H
	 POP DX
	 RET              ;子程序返回
 


DISP ENDP
CODE ENDS
END START