东南大学信息学院微机实验报告九

1、.实验九一、实验目的1.熟悉系统功能调用INT 21H的有关功能2.编写时钟程序二、实验任务1.执行时钟程序时，屏幕上显示提示符“：”，由键盘输入当前时、分、秒值，即XX:XX:XX，随即显示时间并不停地计时。2.当有键盘按下时，立即停止计时，返回DOS。三、源程序DATA SEGMENTBUFFER DB 11 DB ? DB 10 DUP(?)DATA ENDSCODE SEGMENT ASSUME CS:CODE,DS:DATAOUTCLK: MOV AX,DATA MOV DS,AX MOV DL,: MOV AH,2 INT 21H MOV DX,OFFSET BUFFER MOV

2、AH,0AH ;输入字符串 INT 21H MOV BX,OFFSET BUFFER+2 MOV AL,BX ; 时针，ASCII码转非压缩BCD CMP AL, 03AH JAE ERROR1 CMP AL, 02FH JBE ERROR1 AND AL,0FH MOV BX,AL INC BX MOV AL,BX AND AL,0FH MOV BX,AL INC BX INC BX MOV AL,BX ; 分针 AND AL,0FH MOV BX,AL INC BX MOV AL,BX AND AL,0FH MOV BX,AL INC BX INC BX MOV AL,BX ;秒针 AND

3、 AL,0FH MOV BX,AL INC BX MOV AL,BX AND AL,0FH MOV BX,AL MOV BX,OFFSET BUFFER+2 CALL TOBCD ; 时针，两位非压缩BCD转换成两位压缩BCD MOV CH, AL ADD BX,3 CALL TOBCD MOV DH, AL ; 分针，两位非压缩BCD转换成两位压缩BCD MOV DH,AL ADD BX,3 CALL TOBCD ; 秒针，两位非压缩BCD转换成两位压缩BCD MOV DL,AL CMP CH, 24H JAE ERROR CMP DH, 60H JA ERROR CMP DL, 60H J

4、A ERRORERROR1: MOV AH,4CH INT 21H AGAIN: CALL DELAY MOV AL,DL ; 秒针加1 ADD AL,1 DAA MOV DL,AL CMP AL,60H JA ERROR JNE DISPY MOV DL,0 MOV AL,DH ADD AL,1 ; 分针 DAA MOV DH,AL CMP AL,60H JA ERROR JNE DISPY MOV DH,0 MOV AL,CH ADD AL,1 DAA ; 时针 MOV CH,AL CMP AL,24H JAE ERROR JNE DISPY MOV CH,0ERROR: MOV DL,

5、0 MOV DH, 0 MOV CH, 0DISPY: MOV BX,OFFSET BUFFER MOV AL,0DH MOV BX,AL INC BX MOV AL,0 MOV BX,AL INC BX MOV AL,CH CALL TRAN INC BX MOV AL,: MOV BX,AL INC BX MOV AL,DH CALL TRAN INC BX MOV AL,: MOV BX,AL INC BX MOV AL,DL CALL TRAN INC BX MOV AL,$ MOV BX,AL PUSH BX PUSH CX PUSH DX MOV DX,OFFSET BUFFER

6、MOV AH,9 INT 21H MOV AH,06H MOV DL,0FFH INT 21H POP DX POP CX POP BX JNE GO JMP AGAINGO: MOV AH,4CH INT 21HTOBCD PROC ; 两位非压缩BCD转换成压缩 MOV AL,BX MOV CL,4 SHL AL,CL OR AL,BX+1 RETTOBCD ENDPTRAN PROC ; BCD转ASCII MOV CL,AL SHR AL,1 SHR AL,1 SHR AL,1 SHR AL,1 OR AL,30H MOV BX,AL INC BX MOV AL,CL AND AL,0FH OR AL,30H MOV BX,AL RETTRAN ENDPDELAY PROC PUSH CX PUSH AX MOV AX,0FFFFHFIR: MOV CX,02FFFHGOON: DEC CX JNE GOON DEC AX JNE FIR POP AX POP CX RETDELAY ENDPCODE ENDSEND OUTCLK四、思考题时钟程序中存在误差吗？若有误差