原创 12．可预置可逆4位计数器

1．  实验任务<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

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

3、实现程序

1．  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

2．  C语言源程序

#include <AT89X51.H>

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;       //读入P3口开关状态，即读入预置数

  P1=~curcount;                //按位取非

  while(1)

    {

      if(P3_6==0)

        {

          delay10ms();

          if(P3_6==0)

            {

              if(curcount>=15)

                {

                  curcount=0;

                }

                else

                  {

                    curcount++;

                  }

               P1=~curcount;

               while(P3_6==0);

            }

        }

      if(P3_7==0)

        {

          delay10ms();

          if(P3_7==0)

            {

              if(curcount<=0)

                {

                  curcount=15;

                }

                else

                  {

                    curcount--;

                  }

               P1=~curcount;

               while(P3_7==0);

            }

        }

    }

}