How to: Receive Strings From Serial Ports in Visual Basic

How to: Receive Strings From Serial...

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Microsoft Visual Studio 2008/.NET Framework 3.5

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Visual Basic Application Development

How to: Receive Strings From Serial Ports in Visual Basic

This topic describes how to use My.Computer.Ports to receive strings from the computer's serial ports in Visual Basic.

To receive strings from the serial port

Initialize the return string.
Visual Basic
```
Dim returnStr As String = ""
```
Determine which serial port should provide the strings. This example assumes it is COM1.
Use the My.Computer.Ports.OpenSerialPort method to obtain a reference to the port. For more information, see My.Computer.Ports.OpenSerialPort Method.
The Using block allows the application to close the serial port even if it generates an exception. All code that manipulates the serial port should appear within this block, or within a Try...Catch...Finally block.
Visual Basic
```
Using com1 As IO.Ports.SerialPort = _
        My.Computer.Ports.OpenSerialPort("COM1")
End Using
```
Create a Do loop for reading lines of text until no more lines are available.
Visual Basic
```
Do
Loop
```
Use the ReadLine method to read the next available line of text from the serial port.
Visual Basic
```
Dim Incoming As String = com1.ReadLine()
```
Use an If statement to determine if the ReadLine method returns Nothing (which means no more text is available). If it does return Nothing, exit the Do loop.
Visual Basic
```
If Incoming Is Nothing Then
    Exit Do
End If
```
Add an Else block to the If statement to handle the case if the string is actually read. The block appends the string from the serial port to the return string.
Visual Basic
```
Else
    returnStr &= Incoming & vbCrLf
```
Return the string.
Visual Basic
```
Return returnStr
```

Example

Visual Basic

Function ReceiveSerialData() As String
    ' Receive strings from a serial port.
    Dim returnStr As String = ""

    Using com1 As IO.Ports.SerialPort = _
            My.Computer.Ports.OpenSerialPort("COM1")
        Do
            Dim Incoming As String = com1.ReadLine()
            If Incoming Is Nothing Then
                Exit Do
            Else
                returnStr &= Incoming & vbCrLf
            End If
        Loop
    End Using

    Return returnStr
End Function

This code example is also available as an IntelliSense code snippet. In the code snippet picker, it is located in Connectivity and Networking. For more information, see How to: Insert Snippets Into Your Code (Visual Basic).

Compiling the Code

This example assumes the computer is using COM1.

Robust Programming

This example assumes the computer is using COM1. For more flexibility, the code should allow the user to select the desired serial port from a list of available ports. For more information, see How to: Show Available Serial Ports in Visual Basic.

This example uses a Using block to make sure that the application closes the port even if it throws an exception. For more information, see Using Statement (Visual Basic).

Tasks

How to: Dial Modems Attached to Serial Ports in Visual Basic

How to: Send Strings to Serial Ports in Visual Basic

How to: Show Available Serial Ports in Visual Basic

Reference

My.Computer.Ports Object

System.IO.Ports..::.SerialPort