title: SerialPort.ReadExisting() method not returns a string correctly at some times
body: <p>The SerialPort.ReadExisting method not returns my string correctly at some times.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>string Initial="";
  SerialPort sp = new SerialPort { PortName = "COM3", BaudRate = 9600, Parity = Parity.None, StopBits = StopBits.One, DataBits = 8, Handshake = Handshake.None};
  
  sp.Open();
  sp.WriteLine("P");
  Initial = sp.ReadExisting();  // Then Initial must be OK.
  
  if (Initial == "OK")
  { ....}
  </code></pre>
  
  <p>But, the results saying 'O' or 'K' or 'OK'. I dont know why it's happening. How should i avoid this situation and get correct string from serial through ReadExisting() or any other method at all time. </p>
  
  <p>Note: Post your answer with code will more helpful because of newbie in C#.</p>