Applies To:
  • CitectSCADA 5.00

The following information outlines the steps that are to be taken to configure a DDE server and client for the specific example that follows.

DDE Server :
        NT 4.0 Operating System
        Citect version 5.0

DDE Client :
        Win95a Operating System
        Excel 97 SR-1


Part A: The DDE server
  1. Run \WinNT\system32\DDEShare.exe to create a Citect share. This program will pop up a window like this:
  2. Double click the icon on the left to display the current DDE shares.
  3. If there is not already a share called Citect$ then press the Add a share button. If there is an existing share by this name then ensure that is has the following properties.
  4. Set Permissions to allow access to remote users.
  5. Set the share to be available by using the Trust a Share button. Fill in the Trusted share Properties as shown, and press the Set button before OK:
  6. In Citect.ini, you must set the [General]TagDB parameter, so that the Variable Tags database is loaded at compilation (otherwise DDE cannot access the database).
  7. Pack the Citect Database (very important and easy to forget).
  8. Ensure the NetDDE service and the DDEShare application are running. These can be made to fire up automatically on NT startup.
  9. Run Citect.

Part B: The DDE client

  1. Run NetDDE. Assign NetDDE to Windows Startup applications if required.
  2. Run Excel. In a workcell, type
        ='\\<Server Name>\NDDE$'|'Citect$'!'<VariableTagName>'
            <Server Name> is the name of the remote computer, and,
            <VariableTagName> is the Citect Variable tag that you want to read.
  3. The NetDDE connection will require a username and password on the first connection attempt. To avoid this requirement, see TechNet article PSS ID Number: Q172450 " NetDDE Connections Fail When "Logon to" Restrictions Apply".

Additional Notes:

  • Windows 95 does not come with a DDE share manager, so if you want to create shares you will need to use a program such as DDESHR.exe which is a Visual Basic implementation of the Windows for Workgroup DDEShare application. This can be downloaded from the CiT homepage.
  • Excel will not necessarily show #REF or #NA or other error conditions if a connection is lost or if Citect is shut down on the remote PC. To manually update the links, in Excel go to EDIT|Links and hit Update Now.
  • The Excel macro ddeformu.xls that is included with Citect, will not work correctly with NetDDE in this situation, although it can be modified quite easily.