Visual Basic 2010 sample code on how to check com port, checking modem, send AT command and send USER command.
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Visual Basic Source Code
.Imports System.Text
Public Class MainForm
' Declare necessary class variables.
Private CommPort As New RS232()
Private IsModemFound As Boolean = False
Private ModemPort As Integer = 0
' This subroutine checks for available ports on the local machine. It does
' this by attempting to open ports 1 through 4.
Private Sub CheckForPortsButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckForPortsButton.Click
' Check for Availability of each of the 4 Comm Ports, and
' place a check in the list box items that have openable ports.
Dim i As Integer
For i = 1 To 4
WriteMessage("Testing COM" + i.ToString())
If IsPortAvailable(i) Then
' Check the box for available ports.
Me.PortsList.SetItemChecked(i - 1, True)
Else
' Uncheck the box for unavailable ports.
Me.PortsList.SetItemChecked(i - 1, False)
End If
Next
' Enable the Find Modems button.
Me.CheckModemsButton.Enabled = True
End Sub
' This subroutine attempts to send an AT command to any active Comm Ports.
' If a response is returned then a usable modem has been detected
' on that port.
Private Sub CheckModemsButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckModemsButton.Click
Dim i As Integer
For i = 0 To 3
If Me.PortsList.GetItemChecked(i) Then
' Item is checked so it MIGHT be a valid port.
' Test for validity.
If IsPortAvailable(i + 1) Then
' Check if port responds to an AT command.
If IsPortAModem(i + 1) Then
' Set the class variables to the last modem found.
Me.IsModemFound = True
Me.ModemPort = i + 1
' Write message to the user.
WriteMessage("Port " + (i + 1).ToString() + _
" is a responsive modem.")
Else
' Write message to the user.
WriteMessage("Port " + (i + 1).ToString() + _
" is not a responsive modem.")
End If
End If
End If
Next
' If a modem was found, enable the rest of the buttons, so the user
' can interact with the modem.
If Me.IsModemFound Then
Me.SelectedModemTextbox.Text = "Using Modem on COM" + _
Me.ModemPort.ToString()
Me.UserCommandTextbox.Enabled = True
Me.SendATCommandButton.Enabled = True
Me.SendUserCommandButton.Enabled = True
End If
End Sub
' This subroutine clears the TextBox.
Private Sub ClearButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ClearButton.Click
Me.StatusTextbox.Clear()
End Sub
' This subroutine sends an AT command to the modem, and records its response.
' It depends on the timer to do the reading of the response.
Private Sub SendATCommandButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SendATCommandButton.Click
' Always wrap up working with Comm Ports in exception handlers.
Try
' Enable the timer.
Me.tmrReadCommPort.Enabled = True
' Attempt to open the port.
CommPort.Open(ModemPort, 115200, 8, RS232.DataParity.Parity_None, _
RS232.DataStopBit.StopBit_1, 4096)
' Write an AT Command to the Port.
CommPort.Write(Encoding.ASCII.GetBytes("AT" & Chr(13)))
' Sleep long enough for the modem to respond and the timer to fire.
System.Threading.Thread.Sleep(200)
Application.DoEvents()
CommPort.Close()
Catch ex As Exception
' Warn the user.
MessageBox.Show("Unable to communicate with Modem")
Finally
' Disable the timer.
Me.tmrReadCommPort.Enabled = False
End Try
End Sub
' This subroutine sends a user specified command to the modem, and records its
' response. It depends on the timer to do the reading of the response.
Private Sub SendUserCommandButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SendUserCommandButton.Click
' Always wrap up working with Comm Ports in exception handlers.
Try
' Enable the timer.
Me.tmrReadCommPort.Enabled = True
' Attempt to open the port.
CommPort.Open(ModemPort, 115200, 8, RS232.DataParity.Parity_None, RS232.DataStopBit.StopBit_1, 4096)
' Write an user specified Command to the Port.
CommPort.Write(Encoding.ASCII.GetBytes(Me.UserCommandTextbox.Text & Chr(13)))
' Sleep long enough for the modem to respond and the timer to fire.
System.Threading.Thread.Sleep(200)
Application.DoEvents()
CommPort.Close()
Catch ex As Exception
' Warn the user.
MessageBox.Show("Unable to communicate with Modem")
Finally
' Disable the timer.
Me.tmrReadCommPort.Enabled = False
End Try
End Sub
' This subroutine is fired when the timer event is raised. It writes whatever
' is in the Comm Port buffer to the output window.
Private Sub tmrReadCommPort_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tmrReadCommPort.Tick
Try
' As long as there is information, read one byte at a time and
' output it.
While (CommPort.Read(1) <> -1)
' Write the output to the screen.
WriteMessage(Chr(CommPort.InputStream(0)), False)
End While
Catch exc As Exception
' An exception is raised when there is no information to read.
' Don't do anything here, just let the exception go.
End Try
End Sub
' This function checks to see if the port is a modem, by sending
' an AT command to the port. If the port responds, it is assumed to
' be a modem. The function returns a Boolean.
Private Function IsPortAModem(ByVal port As Integer) As Boolean
' Always wrap up working with Comm Ports in exception handlers.
Try
' Attempt to open the port.
CommPort.Open(port, 115200, 8, RS232.DataParity.Parity_None, _
RS232.DataStopBit.StopBit_1, 4096)
' Write an AT Command to the Port.
CommPort.Write(Encoding.ASCII.GetBytes("AT" & Chr(13)))
' Sleep long enough for the modem to respond.
System.Threading.Thread.Sleep(200)
Application.DoEvents()
' Try to get info from the Comm Port.
Try
' Try to read a single byte. If you get it, then assume
' that the port contains a modem. Clear the buffer before
' leaving.
CommPort.Read(1)
CommPort.ClearInputBuffer()
CommPort.Close()
Return True
Catch exc As Exception
' Nothing to read from the Comm Port, so set to False
CommPort.Close()
Return False
End Try
Catch exc As Exception
' Port could not be opened or written to.
Me.PortsList.SetItemChecked(port - 1, False)
MsgBox("Could not open port.", MsgBoxStyle.OKOnly, Me.Text)
Return False
End Try
End Function
' This function attempts to open the passed Comm Port. If it is
' available, it returns True, else it returns False. To determine
' availability a Try-Catch block is used.
Private Function IsPortAvailable(ByVal ComPort As Integer) As Boolean
Try
CommPort.Open(ComPort, 115200, 8, RS232.DataParity.Parity_None, _
RS232.DataStopBit.StopBit_1, 4096)
' If it makes it to here, then the Comm Port is available.
CommPort.Close()
Return True
Catch
' If it gets here, then the attempt to open the Comm Port
' was unsuccessful.
Return False
End Try
End Function
' This subroutine writes a message to the txtStatus TextBox.
Private Sub WriteMessage(ByVal message As String)
Me.StatusTextbox.Text += message + vbCrLf
End Sub
' This subroutine writes a message to the txtStatus TextBox and allows
' the line feed to be suppressed.
Private Sub WriteMessage(ByVal message As String, ByVal linefeed As Boolean)
Me.StatusTextbox.Text += message
If linefeed Then
Me.StatusTextbox.Text += vbCrLf
End If
End Sub
Private Sub ExitToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExitToolStripMenuItem.Click
End
End Sub
End Class
