private void btnReadTag_Click(object sender, EventArgs e)
{
    serialPort = new SerialPort();// if u r not used Serial Port Tool
    serialPort.PortName = "COM1";
    serialPort.BaudRate = 9600;
    serialPort.DataBits = 8;
    serialPort.Parity = Parity.None;
    serialPort.StopBits = StopBits.One;
    serialPort.Open();
    serialPort1.ReadTimeout = 2000;
    serialPort.DataReceived += new SerialDataReceivedEventHandler(Fun_DataReceived);
    serialPort.Close();
}
//Delegate for the Reading the Tag while RFID Card come to the Range.
string data = string.Empty;
private delegate void SetTextDeleg(string text);
void Fun_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
    Thread.Sleep(500);
    data = serialPort.ReadLine();
    this.BeginInvoke(new SetTextDeleg(Fun_IsDataReceived), new object[] { data });
}
private void Fun_IsDataReceived(string data)
{
    txtAccessCardNo.Text = data.Trim();
}