A few days ago I said to myself that I wanted to know more about how to communicate via the serial port. When I first started searching the internet about this subject I found out that it’s not many articles that are discussing this subject and those examples that I found was mostly about the earlier VB6 MSComm control and wrappers for this control. Those matters concerning the MSComm control were not very interesting because I had read that in .NET 2.0 Microsoft had come up with a new serial port control.
As a newbie I have been spending some hours of my time to come up with what I now share with you, but as you all know it’s worth every hour when you succeed. It’s actually not a big deal to do it; it’s just a few lines of code.
Fore those of you who are familiar with the serial port communication I want to recommend this article on the Code Project. It is an excellent article about communicating with mobile phones via the serial port, and it is very clear when you fist know the basic.
The task of this example is very simple. We want to send a text string from one computer via the serial port to another computer. First of all you have to bee in the position that you have 2 computers and second you got to have a “null modem cable”. Another option is that you have 2 serial ports on the computer and connecting them with a “null modem cable”
If you don’t know what a “null modem cable” is then search the internet to see how it is configured.
First of all we want to write to the serial port, and here is the basic.
If you have 2 computers have this one on the first computer. If you have one computer make this a separate project.
In this example you got to have a Button control called
btnSendText and a textBox control called
txtSendText on your form on computer nr1. Just type in some text in the
btnSendText control and Click Button send to send it to COM1.
Public Class Form1
Dim WithEvents Port As SerialPort = _
New SerialPort("COM1", 9600, Parity.None, 8, StopBits.One)
Private Sub btnSendText_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnSendText.Click
Port.Write(txtSendText.Text & "!%")
This is just how simple it is to send a text string to the serial port.
And now how to receive the text string on the other computer.
If you have 2 computers have the next example one on the second computer. If you have one computer make this a separate project, and then run both projects at the same time.
In this example you got to have a Text control called
TextBox1 and a listbox control called
ListBox1 on your form on computer nr2. When clicking send on computer nr1 you will receive it in the textbox1 control on computer nr 2. When the buffer is 0 it will be added to the
Listbox1 control, and
ListBox1 is empty to receive the next incoming text string.
Public Class Form1
Dim WithEvents port As SerialPort = New _
System.IO.Ports.SerialPort("COM1", 9600, Parity.None, 8, StopBits.One)
Private Sub Form1_Load(ByVal sender As Object, ByVal e As _
System.EventArgs) Handles Me.Load
CheckForIllegalCrossThreadCalls = False
If port.IsOpen = False Then port.Open()
Private Sub port_DataReceived(ByVal sender As Object, ByVal e As _
System.IO.Ports.SerialDataReceivedEventArgs) Handles port.DataReceived
TextBox1.Text = (port.ReadTo("!%"))
If port.ReadExisting.Length = 0 Then
TextBox1.Text = ""
The important thing to notice is that you have to declare the port like this “
Dim WithEvents port ...”
You also got to have a “
CheckForIllegalCrossThreadCalls = False” declaration in the in the form load procedure to prevent it from raising an error when a thread other than the creating thread of a control tries to access one of that control's methods or properties. You also have to check if the port is open, and if it’s not open you have to open it.
As you may see that I have some special characters in both the write and the read statement.
port.Write(txtSendText.Text & "!%") and port.ReadTo("!%").
This is because if I put some special characters in the write statement stream I can ask the
readTo statement to read everything until the special character and that is quiet convenient. Just test it.
There are many other options to the serial port communication, and this is only one of them.
I hope it can be of any help to somebody.