51单片机外部中断示例

void Usart_INT0_init()

{

  TMOD = 0X21;

  TH1 = 0XFD;

  TL1 = 0XFD;

  SM0 = 0;

  SM1 = 1;

  REN = 1;

  TR1 = 1;

  //ES = 1;//串口中断影响外部中断0 这句话会让程序无法进入外部中断服务

  TH0 = 0;

  TL0 = 0;

  ET0 = 0;//关闭定时器0

  IT0 = 1;//外部中断下降沿触发*/

  EX0 = 1;//打开外部中断

  EA = 1;

  //ES = 1;

}

void Send_data(unsigned char dat)

{

  SBUF = dat;

  while(!TI);

  TI = 0;

}

int j;

void main()

{

  unsigned int i;

  LED = LED_ON;

  //LED = LED_OFF;

  flag_test_high = ON;

 

  IN0 = 1;

  Usart_INT0_init();

  EX0 = 1;

  while(1)

  {  

       /*i=40000;

    while(i--);*/

    /*flag_test_high = ON;

    EX0 = 1;

    while(flag_test_high == ON);

    EX0 = 0;

    //Send_data('a');*/

    Send_data(result|0x30); 

  }

}

void EX_int(void) interrupt 0

{

  EX0 = 0;

  

  ET0 = 1;//打开定时器

  TR0 = 1;

  while(IN0 == 0);

  TR0 = 0;

  

  tem_TH = TH0;

  tem_TL = TL0;

  sum = tem_TH*256 + tem_TL;

  sum = (int)sum/1000;

  result = 9 - sum;

     //result = 9-(int)(10*(TH0*256 + TL0)/10000);//分步计算避免出错

  TH0 = 0;

  TL0 = 0;

  

  LED = LED_OFF;

  //Send_data(result|0x30);

  flag_test_high = OFF;

  ET0 = 0;//关闭定时器

  EX0 = 1;

}