基于51单片机的计数器设计

1．实验任务
　　利用AT89S51单片机的P1.0－P1.3接四个发光二极管L1－L4，用来指示当前计数的数据；用P1.4－P1.7作为预置数据的输入端，接四个拨动开关K1－K4，用P3.6/WR和P3.7/RD端口接两个轻触开关，用来作加计数和减计数开关。具体的电路原理图如下图所示
2．电路原理图

图4.12.1
3．系统板上硬件连线
（1)．把“单片机系统”区域中的P1.0－P1.3端口用8芯排线连接到“八路发光二极管指示模块”区域中的L1－L4上；要求：P1.0对应着L1，P1.1对应着L2，P1.2对应着L3，P1.3对应着L4；
（2)．把“单片机系统”区域中的P3.0/RXD，P3.1/TXD，P3.2/INT0，P3.3/INT1用导线连接到“四路拨动开关”区域中的K1－K4上； （3)．把“单片机系统”区域中的P3.6/WR，P3.7/RD用导线连接到“独立式键盘”区域中的SP1和SP2上；
4．程序设计内容
（1)．两个独立式按键识别的处理过程；
（2)．预置初值读取的问题
（3)．LED输出指示
5．程序框图

图4.12.2
6．汇编源程序
COUNT              EQU 30H
                            ORG 00H
START:               MOV A,P3
                           ANL A,#0FH
                            MOV COUNT,A
                            MOV P1,A
SK2:           JB P3.6,SK1
                           LCALL DELY10MS
                            JB P3.6,SK1
                            INC COUNT
                           MOV A,COUNT
                            CJNE A,#16,NEXT
                           MOV A,P3
                            ANL A,#0FH
                            MOV COUNT,A
NEXT:                MOV P1,A
WAIT:                 JNB P3.6,WAIT
                           LJMP SK2
SK1:          JB P3.7,SK2
                            LCALL DELY10MS
                            JB P3.7,SK2
                           DEC COUNT
                            MOV A,COUNT
                            CJNE A,#0FFH,NEX
                           MOV A,P3
                            ANL A,#0FH
                            MOV COUNT,A
NEX:                   MOV P1,A
WAIT2:               JNB P3.7,WAIT2
                           LJMP SK2
DELY10MS:       MOV R6,#20
                            MOV R7,#248
D1:                      DJNZ R7,$
                            DJNZ R6,D1
                           RET
                            END
7．C语言源程序
#include
unsigned char curcount;
void delay10ms(void)
{
  unsigned char i,j;
  for(i=20;i>0;i--)
  for(j=248;j>0;j--);
}
void main(void)
{
  curcount=P3 & 0x0f;
  P1=~curcount;
  while(1)
    {
      if(P3_6==0)
        {
          delay10ms();
          if(P3_6==0)
            {
              if(curcount>=15)
                {
                  curcount=15;
                }
                else
                  {
                    curcount++;
                  }
               P1=~curcount;
               while(P3_6==0);
            }
        }
      if(P3_7==0)
        {
          delay10ms();
          if(P3_7==0)
            {
              if(curcount<=0)
                {
                  curcount=0;
                }
                else
                  {
                    curcount--;
                  }
               P1=~curcount;
               while(P3_7==0);
            }
        }
    }
}