Hier ist ein Beispiel mit dem Namespace System.IO.
using System;
using System.IO.Ports;
using System.Windows.Forms;
namespace SerialPortExample
{
  class SerialPortProgram
  {
    
    private SerialPort port = new SerialPort("COM1",
      9600, Parity.None, 8, StopBits.One);
    [STAThread]
    static void Main(string[] args)
    { 
      
      new SerialPortProgram();
    }
    private SerialPortProgram()
    {
      Console.WriteLine("Incoming Data:");
      
      
      port.DataReceived += new 
        SerialDataReceivedEventHandler(port_DataReceived);
      
      port.Open();
      
      Application.Run();
    }
    private void port_DataReceived(object sender,
      SerialDataReceivedEventArgs e)
    {
      
      Console.WriteLine(port.ReadExisting());
    }
  }
}