How To Capture the EOF Character with the MSComm Control (253257)

MORE INFORMATION

This example demonstrates how to create two small sample applications that show how to signal the EOF character. The EOFEnable property must be set to True on the receiving side, and the contents of the MSComm Input buffer must also be read in order for the character to be detected. The following example assumes that a null modem cable is attached between COM1 and COM2. This is only necessary for testing these sample applications. App1 is the COM1 application, App2 is the COM2 application.

Steps to Create App1

1. Create a new Standard EXE project in Visual Basic. Form1 is created by default.
2. On the Project menu, select Components, select Microsoft Comm Control, and then click OK.
3. Add a Command button and an MSComm control to Form1.
4. Add the following code to the General Declarations section of Form1:

   Private Sub Command1_Click()
      MSComm1.Output = Chr$(26)
   End Sub
   
   Private Sub Form_Load()
      Form1.Caption = "App1"
      With MSComm1
         .Handshaking = 2 - comRTS
         .RThreshold = 1
         .RTSEnable = True
         .Settings = "9600,n,8,1"
         .SThreshold = 1
         .PortOpen = True
      End With
      Command1.Caption = "Send"
   End Sub
   
   Private Sub Form_Unload(Cancel As Integer)
      MSComm1.PortOpen = False
   End Sub
   					

Steps to Create App2

1. Start a new instance of Visual Basic specifying a new Standard EXE project. Form1 is created by default.
2. On the Project menu, select Components, select the Microsoft Comm Control, and then click OK.
3. Add an MSComm control to Form1.
4. Add the following code to the General Declarations section of Form1:

   Private Sub Form_Load()
      Form1.Caption = "App2"
      With MSComm1
         .CommPort = 2
         .Handshaking = 2 - comRTS
         .RThreshold = 1
         .RTSEnable = True
         .Settings = "9600,n,8,1"
         .SThreshold = 1
         .PortOpen = True
         .EOFEnable = True
      End With
   End Sub
   
   Private Sub Form_Unload(Cancel As Integer)
      MSComm1.PortOpen = False
   End Sub
   
   Private Sub MSComm1_OnComm()
      Dim InBuff As String
      Select Case MSComm1.CommEvent
      ' Handle each event or error by placing
      ' code below each case statement.
   
      ' This template is found in the Example
      ' section of the OnComm event help topic
      ' in VB help.
   
      ' Errors
         Case comEventBreak   ' A Break was received.
         Case comEventCDTO    ' CD (RLSD) Timeout.
         Case comEventCTSTO   ' CTS Timeout.
         Case comEventDSRTO   ' DSR Timeout.
         Case comEventFrame   ' Framing Error
         Case comEventOverrun ' Data Lost.
         Case comEventRxOver  ' Receive buffer overflow.
         Case comEventRxParity   ' Parity Error.
         Case comEventTxFull  ' Transmit buffer full.
         Case comEventDCB     ' Unexpected error retrieving DCB]
   
      ' Events
         Case comEvCD   ' Change in the CD line.
         Case comEvCTS  ' Change in the CTS line.
         Case comEvDSR  ' Change in the DSR line.
         Case comEvRing ' Change in the Ring Indicator.
         Case comEvReceive ' Received RThreshold # of chars.
            InBuff = MSComm1.Input
         Case comEvSend ' There are SThreshold number of
                        ' characters in the transmit
                        ' buffer.
         Case comEvEOF  ' An EOF character was found in
                        ' the input stream.
            MsgBox "EOF character received!"
      End Select
   End Sub
   					

Steps to Run the Applications

1. Press the F5 key or click the Run button on each project. Position both applications so that you can see them running at the same time.
2. Make sure you have a standard null modem cable connecting the COM1 and COM2 ports.
3. Click the Command button labeled Send on App1, and note that a Message Box displaying the message "EOF character received!" appears in App2.