#define F_CPU 8000000UL
#include <util/delay.h> 		
#include <avr/io.h>    			

int main(void) 
{
	void delay_ms(int d)	//delay in milliseconds
	{
		_delay_ms(d);
	}

	DDRB = 0xFF;    

	while (1) 
	{
		PORTB = 0xAA;
		delay_ms(10);
		
		PORTB = 0x55;
		delay_ms(10);
	} 

	return 0;
}