Check out example codes for "using serial port in c#". It will help you in understanding the concepts better.

Code Example 1

using System;
using System.IO.Ports;
using System.Windows.Forms;

namespace SerialPortExample
{
  class SerialPortProgram
  {
    // Create the serial port with basic settings
    private SerialPort port = new SerialPort("COM1",
      9600, Parity.None, 8, StopBits.One);

    [STAThread]
    static void Main(string[] args)
    { 
      // Instatiate this class
      new SerialPortProgram();
    }

    private SerialPortProgram()
    {
      Console.WriteLine("Incoming Data:");

      // Attach a method to be called when there
      // is data waiting in the port's buffer
      port.DataReceived += new 
        SerialDataReceivedEventHandler(port_DataReceived);

      // Begin communications
      port.Open();

      // Enter an application loop to keep this thread alive
      Application.Run();
    }

    private void port_DataReceived(object sender,
      SerialDataReceivedEventArgs e)
    {
      // Show all the incoming data in the port's buffer
      Console.WriteLine(port.ReadExisting());
    }
  }
}

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