const int latchPin = PB5;   //RCLK
const int clockPin = PB3;   //SRCLK
const int dataPin = PB4;    //SER

byte leds = 0;	

void setup() {
  
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}

void loop() 
{
  leds = 0;	// Turn all the LEDs off
  updateShiftRegister();
  delay(500);
  for (int i = 0; i < 8; i++)	// Turn all the LEDs ON one by one.
  {
    bitSet(leds, i);		// Set the bit that controls that LED in the variable 'leds'
    updateShiftRegister();
    delay(500);
  }
}

/*
 * updateShiftRegister() - This function sets the latchPin to low, then calls the Arduino function 'shiftOut' to shift out contents of variable 'leds' in the shift register before putting the 'latchPin' high again.
 */
void updateShiftRegister()
{
   digitalWrite(latchPin, LOW);
   shiftOut(dataPin, clockPin, LSBFIRST, leds);
   digitalWrite(latchPin, HIGH);
}