byte MaskB;

void setup(){
  MaskB = 0b000001;
  DDRB = MaskB;

}

void loop(){
   static byte sec = 0, min = 0, hour = 0;
   sec++;
   delay(1000);

   if(sec >= 59) {
    sec = 0;
    min++;
    if(min >= 59){
      min = 0;
      hour++;
      if(hour >=24) hour = 0;
    }
   }
/*   
   if(PORTB &(1<<PB0))
   PORTB &= ~(1<<PB0);
   else
   PORTB |= (1<<PB0);
*/
  PORTB = sec;
}