Serial reading

public class NewBehaviourScript : MonoBehaviour
{
    public string recievedData;
    public GameObject cube;
    Vector3 rotationVal;
    SerialPort microcontroller = new SerialPort("COM4");
    void Start()
    {


        microcontroller.BaudRate = 9600;
        microcontroller.Parity = Parity.None;
        microcontroller.StopBits = StopBits.One;
        microcontroller.DataBits = 8;
        microcontroller.Handshake = Handshake.None;
        microcontroller.RtsEnable = true;
        microcontroller.DtrEnable = true;
        microcontroller.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);

        microcontroller.Open();

        
    }

    private void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)       
    {

        SerialPort sp = (SerialPort)sender;
        Debug.Log("Recieving");
        string data = sp.ReadLine();
        rotationVal = new Vector3(0, float.Parse(data), 0);
    }

    void Update()
    {
        cube.transform.eulerAngles = rotationVal;
    }

}