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Q209077: PRB: CommCtl: No "OK" Received When Using Some Modems

Article: Q209077
Product(s): Microsoft Visual Basic for Windows
Version(s): 3.0
Operating System(s): 
Keyword(s): kbToolkit kbVBp500 kbVBp600 kbOSWinCEsearch kbGrpDSVB kbGrpDSVBDB
Last Modified: 16-NOV-2001

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The information in this article applies to:

- Microsoft eMbedded Visual Basic, version 3.0 
- Microsoft Windows CE Toolkit for Visual Basic 6.0 
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SYMPTOMS
========

Some modems may not respond with an OK in the Input string of the Communications
control when an AT command has been sent.

CAUSE
=====

Modems may not respond if the Data Terminal Ready (DTR) signal is low. You may
need to raise the DTR signal before opening the Communications port.

Note that the Communication control only checks the DTREnable property when the
port is being opened. If the DTREnable property is set to True after opening the
port, the DTR signal does not change until the port is closed and reopened.

RESOLUTION
==========

To get the modem to respond with an OK, set the DTREnable property of the
Communication control to True prior to opening the communications port.

NOTE: This will not necessarily work for all modems.

STATUS
======

This behavior is by design.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Create a new Windows CE project in either Visual Basic or eMbedded Visual
  Basic. Form1 is created by default.

2. From the Project menu, choose Components. In the Components dialog box, click
  the Controls tab, then select the Microsoft CE Comm Control.

3. Place a command button (named Command1), a text box (named Text1) and a Comm
  control (named Comm1) on Form1.

4. Paste the following code into Form1:

     Option Explicit
     Dim InBuff

     Private Sub Comm1_OnComm()
         If Comm1.CommEvent = comEvReceive Then
            InBuff = InBuff & Comm1.Input
            Text1.Text = InBuff
         End If
     End Sub

     Private Sub Command1_Click()
         Comm1.RTSEnable = True
         Comm1.Settings = "9600,n,8,1"
         Comm1.RThreshold = 1
         Comm1.SThreshold = 1
         Comm1.CommPort = 2
         Comm1.PortOpen = True
         Comm1.Output = "AT" & vbCrLf
     End Sub

     Private Sub Form_Unload(Cancel As Integer)
         Comm1.PortOpen = False
     End Sub

5. Run the project on the device.

RESULTS: The OK does not come back from the modem.

REFERENCES
==========

Microsoft eMbedded Visual Basic 3.0 Online Help

Microsoft Windows CE Toolkit for Visual Basic 6.0 Online Help

Additional query words: kbdse vbce evb vbce6

======================================================================
Keywords          : kbToolkit kbVBp500 kbVBp600 kbOSWinCEsearch kbGrpDSVB kbGrpDSVBDB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword2 kbVBeMbSearch kbWinCETKVBSearch kbWinCESearch kbVBeMb300
Version           : :3.0
Issue type        : kbprb

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