PRB: CommCtl: No "OK" Received When Using Some Modems (209077)


The information in this article applies to:

  • Microsoft eMbedded Visual Basic 3.0
  • Microsoft Windows CE Toolkit for Visual Basic 6.0
This article was previously published under Q209077

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
Modification Type:MajorLast Reviewed:10/20/2003
Keywords:kbprb kbToolkit KB209077
©2003 Microsoft Corporation. All rights reserved.