atmega8 Example: Delay of system library function

/*********************************************************** 

* Library Description: ATMEGE8 Delay Library Function 

* Version: v1.0                                                                                          

*                                                                                           

************************************************************ 

*Note: LED PC5                                             

***********************************************************/  

#include  

//Define external crystal  

#define F_CPU 6000000UL  

// Delay including header files  

#include  

// Function declaration  

void Delay_s(int ss);  

int main(void)  

{  

    //LED etc. PC5 is set as output  

    DDRC |= (1 << DDC5);  

    //Start with PC5 outputting high level, LED is off  

    PORTC |= (1 << PC5);  

    while(1)  

    {  

        //Return  

        PORTC ^= (1 << PC5);  

        //Delay 1s  

        Delay_s(1);  

    }      

    return 0;  

}  

/*********************************************************** 

** Name: void Delay_s(int ss) 

** Function: Accurate 1s delay 

** Input parameter: ss The number of seconds to delay 

** Export parameters: None 

** Instructions: System library function delays are limited by the size of the crystal oscillator 

***********************************************************/  

void Delay_s(int ss)  

{  

    int i = 0;  

    while(ss--)  

    {  

        for(i = 0; i < 25; i++)  

        {     

            _delay_ms(40);  

        }  

    }  

}  

//First, F_CPU (i.e., crystal frequency) is no longer defined in the library file , so define it yourself in main.c.

// And the system delay function has restrictions on the delay size due to different crystal oscillators, please note:

/** 

   \ingroup util_delay 

   Perform a delay of \c __us microseconds, using _delay_loop_1(). 

   The macro F_CPU is supposed to be defined to a 

   constant defining the CPU clock frequency (in Hertz). 

   The maximal possible delay is 768 us / F_CPU in MHz. 

 */  

/** 

   \ingroup util_delay 

   Perform a delay of \c __ms milliseconds, using _delay_loop_2(). 

   The macro F_CPU is supposed to be defined to a 

   constant defining the CPU clock frequency (in Hertz). 

   The maximal possible delay is 262.14 ms / F_CPU in MHz. 

 */