According to Microsoft MSDN and using MSComm, all you need to do is:
Use the MSComm control in Visual Basic .NET to access serial ports
Because no Microsoft .NET Framework classes exist to access the communications resources that connected to your computer, you can use the MSComm control in Microsoft Visual Basic 6.0. The MSComm control provides serial communications for your application by enabling the transmission and reception of data through a serial port. To implement basic serial communications by using a modem, follow these steps:
(There are some caveats: This example uses 9600 baud, only applicable up to VB.net 2003 and to establish communication with the LPTx port, you must stop the Print Spooler service. To do this, use the Services tool)
in Administrative Tools.
Start Microsoft Visual Studio .NET.
On the File menu, point to New, and then click Project.
Under Project Types, click Visual Basic Projects.
Under Templates, click Console Application.
In the Name box, type MyConsoleApplication, and then click OK.
By default, Module1.vb is created.
Right-click the MyConsoleApplication project, and then click Add Reference.
Click the COM tab, click Microsoft Comm Control 6.0 under Component Name, click Select, and then click OK.
Note To use the MSComm control, you must install the related COM components of Microsoft Visual Basic 6.0 on the same computer that has Microsoft Visual Studio .NET installed.
For more information about license issues when you use Visual Basic 6.0 controls in Visual Studio .NET, click the following article number to view the article in the Microsoft Knowledge Base:
318597 Errors when you use Visual Basic 6.0 controls in Visual Studio .NET
Replace the code in Module1.vb with the following code example.
Imports MSCommLib
Module Module1
Sub Main()
'New a MSComm control
Dim MSComm1 As MSComm
MSComm1 = New MSComm
' Buffer to hold input string.
Dim Buffer As String
' Use the COM1 serial port.
MSComm1.CommPort = 1
' 9600 baud, no parity, 8 data, and 1 stop bit.
MSComm1.Settings = "9600,N,8,1"
' Tell the control to read the whole buffer when Input is used.
MSComm1.InputLen = 0
' Open the serial port.
MSComm1.PortOpen = True
Console.WriteLine("Open the serial port.")
' Tell the control to make the Input property return text data.
MSComm1.InputMode() = InputModeConstants.comInputModeText
'Clear the receive buffer.
MSComm1.InBufferCount() = 0
' Send the attention command to the modem.
MSComm1.Output = "ATV1Q0" & Chr(13)
Console.WriteLine("Send the attention command to the modem.")
Console.WriteLine("Wait for the data to come back to the serial port...")
' Make sure that the modem responds with "OK".
' Wait for the data to come back to the serial port.
Do
Buffer = Buffer & MSComm1.Input
Loop Until InStr(Buffer, "OK" & vbCrLf)
' Read the "OK" response data in the serial port.
' Close the serial port.
Console.WriteLine("Read the OK response data in the serial port.")
MSComm1.PortOpen = False
Console.WriteLine("Close the serial port.")
End Sub
End Module
Use platform invoke services to call Win32 API functions in Visual Basic .NET to access serial and parallel ports
To do this, follow these steps:
Start Microsoft Visual Studio .NET.
On the File menu, point to New, and then click Project.
Under Project Types, click Visual Basic Projects.
Under Templates, click Console Application.
In the Name text box, type MyConsoleApplication, and then click OK.
By default, Module1.vb is created.
Add the following code to Module1.vb before the Module Module1 statement:
Option Strict On
' Define a CommException class that inherits from the ApplicationException class,
' and then throw an object of type CommException when you receive an error message.
Class CommException
Inherits ApplicationException
Sub New(ByVal Reason As String)
MyBase.New(Reason)
End Sub
End Class
Declare structures, constants, and references to external functions that are in Kernel32.dll
To call unmanaged functions from your managed Visual Basic .NET application, you must declare references to the structures that you pass as parameters to the unmanaged functions, and you must declare the constants that you pass as parameters to the unmanaged functions. To do this, add the following code to Module1.vb after the Module Module1 statement:
'Declare structures.
Public Structure DCB
Public DCBlength As Int32
Public BaudRate As Int32
Public fBitFields As Int32 'See Comments in Win32API.Txt
Public wReserved As Int16
Public XonLim As Int16
Public XoffLim As Int16
Public ByteSize As Byte
Public Parity As Byte
Public StopBits As Byte
Public XonChar As Byte
Public XoffChar As Byte
Public ErrorChar As Byte
Public EofChar As Byte
Public EvtChar As Byte
Public wReserved1 As Int16 'Reserved; Do Not Use
End Structure
Public Structure COMMTIMEOUTS
Public ReadIntervalTimeout As Int32
Public ReadTotalTimeoutMultiplier As Int32
Public ReadTotalTimeoutConstant As Int32
Public WriteTotalTimeoutMultiplier As Int32
Public WriteTotalTimeoutConstant As Int32
End Structure
'Declare constants.
Public Const GENERIC_READ As Int32 = &H80000000
Public Const GENERIC_WRITE As Int32 = &H40000000
Public Const OPEN_EXISTING As Int32 = 3
Public Const FILE_ATTRIBUTE_NORMAL As Int32 = &H80
Public Const NOPARITY As Int32 = 0
Public Const ONESTOPBIT As Int32 = 0
'Declare references to external functions.
Public Declare Auto Function CreateFile Lib "kernel32.dll" _
(ByVal lpFileName As String, ByVal dwDesiredAccess As Int32, _
ByVal dwShareMode As Int32, ByVal lpSecurityAttributes As IntPtr, _
ByVal dwCreationDisposition As Int32, ByVal dwFlagsAndAttributes As Int32, _
ByVal hTemplateFile As IntPtr) As IntPtr
Public Declare Auto Function GetCommState Lib "kernel32.dll" (ByVal nCid As IntPtr, _
ByRef lpDCB As DCB) As Boolean
Public Declare Auto Function SetCommState Lib "kernel32.dll" (ByVal nCid As IntPtr, _
ByRef lpDCB As DCB) As Boolean
Public Declare Auto Function GetCommTimeouts Lib "kernel32.dll" (ByVal hFile As IntPtr, _
ByRef lpCommTimeouts As COMMTIMEOUTS) As Boolean
Public Declare Auto Function SetCommTimeouts Lib "kernel32.dll" (ByVal hFile As IntPtr, _
ByRef lpCommTimeouts As COMMTIMEOUTS) As Boolean
Public Declare Auto Function WriteFile Lib "kernel32.dll" (ByVal hFile As IntPtr, _
ByVal lpBuffer As Byte(), ByVal nNumberOfBytesToWrite As Int32, _
ByRef lpNumberOfBytesWritten As Int32, ByVal lpOverlapped As IntPtr) As Boolean
Public Declare Auto Function ReadFile Lib "kernel32.dll" (ByVal hFile As IntPtr, _
ByVal lpBuffer As Byte(), ByVal nNumberOfBytesToRead As Int32, _
ByRef lpNumberOfBytesRead As Int32, ByVal lpOverlapped As IntPtr) As Boolean
Public Declare Auto Function CloseHandle Lib "kernel32.dll" (ByVal hObject As IntPtr) As Boolean
Before you can access a serial port or a parallel port, you must obtain a handle to the appropriate port and then configure the port communications. To do this, add the following initialization code to Module1.vb after the Sub Main statement.
Note To establish communication with the LPTx port, you must stop the Print Spooler service. To do this, use the Services tool in Administrative Tools.
' Declare the local variables that you will use in the code.
Dim hSerialPort, hParallelPort As IntPtr
Dim Success As Boolean
Dim MyDCB As DCB
Dim MyCommTimeouts As COMMTIMEOUTS
Dim BytesWritten, BytesRead As Int32
Dim Buffer() As Byte
' Declare the variables to use for encoding.
Dim oEncoder As New System.Text.ASCIIEncoding
Dim oEnc As System.Text.Encoding = oEncoder.GetEncoding(1252)
' Convert String to Byte().
Buffer = oEnc.GetBytes("Test")
Try
' Access the serial port.
Console.WriteLine("Accessing the COM1 serial port")
' Obtain a handle to the COM1 serial port.
hSerialPort = CreateFile("COM1", GENERIC_READ Or GENERIC_WRITE, 0, IntPtr.Zero, _
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, IntPtr.Zero)
' Verify that the obtained handle is valid.
If hSerialPort.ToInt32 = -1 Then
Throw New CommException("Unable to obtain a handle to the COM1 port")
End If
' Retrieve the current control settings.
Success = GetCommState(hSerialPort, MyDCB)
If Success = False Then
Throw New CommException("Unable to retrieve the current control settings")
End If
' Modify the properties of the retrieved DCB structure as appropriate.
' WARNING: Make sure to modify the properties according to their supported values.
MyDCB.BaudRate = 9600
MyDCB.ByteSize = 8
MyDCB.Parity = NOPARITY
MyDCB.StopBits = ONESTOPBIT
' Reconfigure COM1 based on the properties of the modified DCB structure.
Success = SetCommState(hSerialPort, MyDCB)
If Success = False Then
Throw New CommException("Unable to reconfigure COM1")
End If
' Retrieve the current time-out settings.
Success = GetCommTimeouts(hSerialPort, MyCommTimeouts)
If Success = False Then
Throw New CommException("Unable to retrieve current time-out settings")
End If
' Modify the properties of the retrieved COMMTIMEOUTS structure as appropriate.
' WARNING: Make sure to modify the properties according to their supported values.
MyCommTimeouts.ReadIntervalTimeout = 0
MyCommTimeouts.ReadTotalTimeoutConstant = 0
MyCommTimeouts.ReadTotalTimeoutMultiplier = 0
MyCommTimeouts.WriteTotalTimeoutConstant = 0
MyCommTimeouts.WriteTotalTimeoutMultiplier = 0
' Reconfigure the time-out settings, based on the properties of the modified COMMTIMEOUTS structure.
Success = SetCommTimeouts(hSerialPort, MyCommTimeouts)
If Success = False Then
Throw New CommException("Unable to reconfigure the time-out settings")
End If
' Write data to COM1.
Console.WriteLine("Writing the following data to COM1: Test")
Success = WriteFile(hSerialPort, Buffer, Buffer.Length, BytesWritten, IntPtr.Zero)
If Success = False Then
Throw New CommException("Unable to write to COM1")
End If
' Read data from COM1.
Success = ReadFile(hSerialPort, Buffer, BytesWritten, BytesRead, IntPtr.Zero)
If Success = False Then
Throw New CommException("Unable to read from COM1")
End If
Catch ex As Exception
Console.WriteLine(Ex.Message)
Finally
' Release the handle to COM1.
Success = CloseHandle(hSerialPort)
If Success = False Then
Console.WriteLine("Unable to release handle to COM1")
End If
End Try
Try
' Parallel port.
Console.WriteLine("Accessing the LPT1 parallel port")
' Obtain a handle to the LPT1 parallel port.
hParallelPort = CreateFile("LPT1", GENERIC_READ Or GENERIC_WRITE, 0, IntPtr.Zero, _
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, IntPtr.Zero)
' Verify that the obtained handle is valid.
If hParallelPort.ToInt32 = -1 Then
Throw New CommException("Unable to obtain a handle to the LPT1 port")
End If
' Retrieve the current control settings.
Success = GetCommState(hParallelPort, MyDCB)
If Success = False Then
Throw New CommException("Unable to retrieve the current control settings")
End If
' Modify the properties of the retrieved DCB structure as appropriate.
' WARNING: Make sure to modify the properties according to their supported values.
MyDCB.BaudRate = 9600
MyDCB.ByteSize = 8
MyDCB.Parity = NOPARITY
MyDCB.StopBits = ONESTOPBIT
' Reconfigure LPT1 based on the properties of the modified DCB structure.
Success = SetCommState(hParallelPort, MyDCB)
If Success = False Then
Throw New CommException("Unable to reconfigure LPT1")
End If
' Retrieve the current time-out settings.
Success = GetCommTimeouts(hParallelPort, MyCommTimeouts)
If Success = False Then
Throw New CommException("Unable to retrieve current time-out settings")
End If
' Modify the properties of the retrieved COMMTIMEOUTS structure as appropriate.
' WARNING: Make sure to modify the properties according to their supported values.
MyCommTimeouts.ReadIntervalTimeout = 0
MyCommTimeouts.ReadTotalTimeoutConstant = 0
MyCommTimeouts.ReadTotalTimeoutMultiplier = 0
MyCommTimeouts.WriteTotalTimeoutConstant = 0
MyCommTimeouts.WriteTotalTimeoutMultiplier = 0
' Reconfigure the time-out settings, based on the properties of the modified COMMTIMEOUTS structure.
Success = SetCommTimeouts(hParallelPort, MyCommTimeouts)
If Success = False Then
Throw New CommException("Unable to reconfigure the time-out settings")
End If
' Write data to LPT1.
' Note: You cannot read data from a parallel port by calling the ReadFile function.
Console.WriteLine("Writing the following data to LPT1: Test")
Success = WriteFile(hParallelPort, Buffer, Buffer.Length, BytesWritten, IntPtr.Zero)
If Success = False Then
Throw New CommException("Unable to write to LPT1")
End If
Catch ex As Exception
Console.WriteLine(Ex.Message)
Finally
' Release the handle to LPT1.
Success = CloseHandle(hParallelPort)
If Success = False Then
Console.WriteLine("Unable to release handle to LPT1")
End If
End Try
Console.WriteLine("Press ENTER to quit")
Console.ReadLine()
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