//Is a AVR codes to blink a LED

#include <avr/io.h>
#include <util/delay.h>
#define led PB4
#define pb PB3 

int main ()
{
  DDRB |= (1 << led); //config PB4(led) as output

  while (1)
  {
  
  PORTB |= (1 << led); //set PB4 high, ie turn on led
  _delay_ms (500);  //500ms delay
  
  PORTB &= !(1 << led); //set PB4 high, ie turn off led
  _delay_ms (500);  //500ms delay
  
  }
}