void setup() 
{
  DDRB |= 1<<0;
  DDRB |= 1<<1;
}

void loop()
{
 PORTB &= ~(1<<1); 
 PORTB |= 1<<0;
 delay(500);
 PORTB &= ~(1<<0);
 PORTB |= 1<<1;  
 delay(500);
}