icp.c

采用Atmega16的变频式超声波发生器的源代码

#include"main.h"


extern volatile uchar icp_overflow;
extern const uchar xtal;
extern volatile ulong icp_time;



ISR(SIG_INPUT_CAPTURE3)
{
static uint icp_time_old;
static uchar icp_flag=0;
 switch(icp_flag)
 {
 case 0:
        icp_flag++;
        TCNT3=0;
        break;
 case 1:icp_time_old=ICR3;
        icp_flag++;
		icp_overflow=0;
		break;
 case 2:  
          
          if(ICR3>=icp_time_old)
          icp_time=(ulong) (ICR3-icp_time_old+icp_overflow*65536);
		  else
          icp_time=(ulong) (icp_overflow*65536+icp_time_old-ICR3);
          cbi(ETIMSK,TICIE3);
          cbi(ETIMSK,TOIE3);
          icp_flag=0;
		  
		  TCNT3=0;
        
		break;
}
 
}

ISR(SIG_OVERFLOW3)
{
icp_overflow++;
} 
   


void icp(void)   //timer3 PE7--ICP
{
icp_time=0;
ulong f;


TCCR3B|=(1<<ICNC3)|(1<<CS30);  
//noise canceler,falling edge trigger,no prescaler 

sbi(ETIMSK,TICIE3);
//Timer3 Input Capture Interrupt Enable
sbi(ETIMSK,TOIE3);
//Timer3 Overflow Interrupt Enable
sei();

while(icp_time==0);
f=(ulong) xtal*1000*1000/icp_time;



write_dec(f);
write_data('h');
write_data('z');



}