四人抢答器.asm

MD51-86实现的四人抢答器

STACK SEGMENT STACK
   DW 64 DUP(?)
STACK ENDS
DATA SEGMENT
   LED DB 06H,5BH,4FH,66H ;1-4的数码表
DATA ENDS
CODE SEGMENT
   ASSUME CS:CODE,DS:DATA
  START:  MOV AX,DATA
          MOV DS,AX
          MOV DX,63H         ;设8255为A口输出，B口输入
          MOV AX,82H
          OUT DX,AL
          MOV BX,OFFSET LED   ;使BX指向段码管首址

      D:  MOV AL,3FH  
          MOV DX,60H
          OUT DX,AL
          
          MOV DX,61H
          IN AL,DX
          AND AL,80H
          JZ A
          JMP D

      A:  MOV DL,07H
          MOV AL,00H           ;灭灯           
          MOV DX,60H                     
          OUT DX,AL

          MOV DX,61H
          IN AL,DX            ;从8255的B口输入数据
          OR AL,AL            ;比较是否为0
          JE A                ;若为0，则表明无键按下，转A      
          MOV CL,0FFH         ;CL作计数器，初值为-1      
      B:  SHR AL,1               
          INC CL
          JNC B
          MOV AL,CL
          XLAT
          MOV DX,60H
          OUT DX,AL
          MOV DL,07H           ;响铃ASC码为07
          
      E:  MOV DX,61H
          IN AL,DX
          AND AL,80H
          JNZ D
          JMP E
CODE ENDS
   END START