Communicating With Serial Port In C#

This article will demonstrate how to write and receive data from a device connected to a serial port in C# and .NET. We will be writing the received data to a TextBox on a form, so this will also deal with threading.

In the past, to communicate with a Serial Port using .Net 1.1, you had to either use the Windows API, or use a third-party control. With .Net 2.0, Microsoft added this support with the inclusion of the SerialPort class as part of the System.IO.Ports namespace. Implementation of the SerialPort class is very straight-forward. To create an instance of the SerialPort class, you simply pass the SerialPort options to the constructor of the class:

  1. // all of the options for a serial device  
  2.     // ---- can be sent through the constructor of the SerialPort class  
  3.     // ---- PortName = "COM1", Baud Rate = 19200, Parity = None,  
  4.     // ---- Data Bits = 8, Stop Bits = One, Handshake = None  
  5.     SerialPort _serialPort = new SerialPort("COM1", 19200, Parity.None, 8, StopBits.One);  
  6.     _serialPort.Handshake = Handshake.None;   

To receive data, we will need to create an EventHandler for the "SerialDataReceivedEventHandler":

  1. // "sp_DataReceived" is a custom method that I have created  
  2.     _serialPort.DataReceived += new SerialDataReceivedEventHandler(sp_DataReceived);  

You can also set other options, such as the ReadTimeout and WriteTimeout, 

  1. // milliseconds _serialPort.ReadTimeout = 500;  
  2. _serialPort.WriteTimeout = 500;  

Once you are ready to use the Serial Port, you will need to open it: 

  1. // Opens serial port   
  2. _serialPort.Open();   

Now we are ready to receive data. However, to write this data to the TextBox on a form, we need to create a delegate. .Net does not allow cross-thread action, so we need to use a delegate. The delegate is used to write to the UI thread from a non-UI thread.

  1. // delegate is used to write to a UI control from a non-UI thread  
  2. private delegate void SetTextDeleg(string text);  

We will now create the "sp_DataReceived" method that will be executed when data is received through the serial port, 

  1. void sp_DataReceived(object sender, SerialDataReceivedEventArgs e)  
  2. {  
  3.     Thread.Sleep(500);  
  4.     string data = _serialPort.ReadLine();  
  5.     // Invokes the delegate on the UI thread, and sends the data that was received to the invoked method.  
  6.     // ---- The "si_DataReceived" method will be executed on the UI thread which allows populating of the textbox.  
  7.     this.BeginInvoke(new SetTextDeleg(si_DataReceived), new object[] { data });  
  8. }  

Now we create our "si_DataReceived" method, 

  1. private void si_DataReceived(string data) { textBox1.Text = data.Trim(); }  

We can now receive data from a serial port device and display it on a form. Some devices will send data without being prompted. However, some devices need to be send certain commands, and it will reply with the data that the command calls for. For these devices, you will write data to the serial port, and use the previous code to get the data that will be sent back. In my example, I will be communicating with a scale. For this particular scale, sending the command "SI\r\n" will force it to return the weight of whatever is on the scale. This command is specific for this scale. You will need to read the documentation of your serial device to find commands that it will receive. To write to the serial port, I have created a "Start" button on the form. I have added code to it's Click_Event:

  1. private void btnStart_Click(object sender, EventArgs e)  
  2. {  
  3.     // Makes sure serial port is open before trying to write  
  4.     try  
  5.     {  
  6.         if(!(_serialPort.IsOpen))  
  7.         _serialPort.Open();  
  8.         _serialPort.Write("SI\r\n");  
  9.     }  
  10.     catch (Exception ex)  
  11.     {  
  12.         MessageBox.Show("Error opening/writing to serial port :: " + ex.Message, "Error!");  
  13.     }  
  14. }  

And that is all you need to do. I have attached the Visual Studio 2005 solution.