blinky.c

// set these fuse bits to 0:
// CKDIV8, SUT0, CKSEL3, CKSEL2, and CKSEL0

// the CPU clock is 31250 Hz
#define F_CPU 31250

#include <avr/io.h>
#include <avr/power.h>
#include <util/delay.h>

int main(void)
{
	// set pre-scaler of the 8 MHz RC oscillator to 256, for a 31250 Hz clock
	clock_prescale_set(clock_div_256);

	// all pins as output
	DDRB = 0xff;

	// 1 Hz blinky
	while (1) {
		PORTB = 0xff;
		_delay_ms(500);
		PORTB = 0;
		_delay_ms(500);
	}
  
	return 0;
}