gistfile1.cpp

int pin_data = 13;
int pin_latch = 12;
int pin_clock = 11;
int shift_register[8];

void setup() {
  pinMode(pin_data, OUTPUT);
  pinMode(pin_latch, OUTPUT);
  pinMode(pin_clock, OUTPUT);
  pinMode(7, OUTPUT);
  Serial.begin(9600);
  resetShiftRegister();
}

void loop() {
  digitalMultiWrite(15, 1);
  digitalMultiWrite(7, 0);
  delay(1000);
  digitalMultiWrite(15, 0);
  digitalMultiWrite(7, 1);
  delay(1000);
}

void digitalMultiWrite(int pin, int voltage) {
  if (pin <= 13) {
    digitalWrite(pin, voltage);
  } else {
    int shift_pin = pin - 14;
    Serial.println(shift_pin);
    shift_register[shift_pin] = voltage;
    sendShiftRegister();
  }
}

void resetShiftRegister() {
  for (int i = 0; i<8; i++) {
    shift_register[i] = 0;
  }
}

void sendShiftRegister() {
  int value = shift_register[0] + 
              shift_register[1] *   2 +
              shift_register[2] *   4 +
              shift_register[3] *   8 +
              shift_register[4] *  16 +
              shift_register[5] *  32 +
              shift_register[6] *  64 +
              shift_register[7] * 128;
  digitalWrite(pin_latch, LOW);
  shiftOut(pin_data, pin_clock, MSBFIRST, value);
  digitalWrite(pin_latch, HIGH);
  Serial.println(value);
}