ORG 0000H
           LJMP MAIN
            ORG 000BH
            LJMP IT0P
            ORG 0100H
   MAIN: MOV SP,#60H
            MOV TMOD,#61H
            MOV TL0,#0B0H
            MOV TH0,#3CH
            SETB ET0
            MOV TL1,#00H
            MOV TH1,#00H
            SETB ET1
            SETB TR0
            SETB EA
            JNB P3.2,W
            CLR TR1
                W:SETB TR1               
          LCALL CZ
      CZ:MOV A,TL1
   MOV B,#100
              DIV AB
            MOV 30H,A
            MOV A,B
            MOV B,#10
            DIV AB
            MOV 31H,A
            MOV 32H,B
         LCALL DISP
     IT0P: MOV TL0,#0B0H
             MOV TH0,#3CH
            CPL P3.0
                RETI
     DISP:MOV R0,#30H
             MOV R2,#0FBH
            MOV R3,#0FFH
   DISP1:MOV A,#0FFH
            MOV P1,A
            MOV A,@R0
            MOV DPTR,#TABLE
            MOVC A,@A+DPTR
            MOV P2,A
            MOV A,R2
            MOV P1,A
   DISP2:DJNZ R3,DISP2
            INC R0
            MOV A,R2
            CLR C
            RR A
            MOV R2,A
            JB ACC.7,DISP1
            RET
   TABLE:DB 3FH,06H,5BH,4FH,66H,6DH,7DH,07H,7FH
            DB 6FH,77H,7CH,39H,5EH,79H,71H,00H,40H,0F3H
            END

1.采用T0定时器中断方式模拟外部计数脉冲，脉冲周期设为200ms
2.采用T1定时器对外部脉冲计数（假设计数不超过255）
3.设计3位动态数码管显示接口，随时读取计数值送到数码管显示
4.外部增加一个开关控制计数的开始和暂停