#define SHCP 2 // Clock
#define STCP 3 // Storage Register Clock Input (latch)
#define DS 4 // Serial Input (Data)

void setup() {
  pinMode(SHCP, OUTPUT);
  pinMode(STCP, OUTPUT);
  pinMode(DS, OUTPUT);
}

void loop() {
  for (int n = 0; n < 256; n++) {
    digitalWrite(STCP, LOW); // hold the value.
    shiftOut(DS, SHCP, MSBFIRST, n);
    digitalWrite(STCP, HIGH); // flush the value to the outputs.
    delay(500);
  }
}