Network DDE:
Network DDE, referred to as NetDDE, is an extension of the DDE available in Windows. It provides information-sharing capabilities by opening two one-way pipes between
applications. Network DDE is an extension of Dynamic Data Exchange (DDE) that can be used between two computers across the network.
Under Windows 95 or Windows NT, NetDDE allows a DDE client on one computer to read from and/or write to a DDE server on a different computer.
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For example, RSLinx could be running on one computer, and RSView32 or Excel could be running on a different computer.They could exchange data using DDE in much the same way as if they both resided on the same computer.
NetDDE takes all of the capabilities of DDE and extends this capability across the Windows network. NetDDE is not a special form of DDE; rather it involves a redirector that runs in the background on a Windows workstation searching for particular
information contained in a DDE conversation.
One of the advantages of the implementation of NetDDE in Windows is that it requires no changes to any DDE-aware (compatible) applications (i.e., software programs that can communicate via DDE). All DDE-aware applications can take advantage of Network DDE.
Note: For Windows NT systems, Network DDE Services must be set up and started; they are not automatically started. You must have Windows NT administrator privileges to complete these procedures.
For a Windows 95 environment, you must manually start NETDDE.EXE before using Network DDE. Also, Rockwell Software is currently working on a utility to create DDE shares in Windows 95. For more information on this utility, contact Technical Support at 440-646-7801.
WARNING: Do not use NetDDE for moderate to heavy data applications. It is best used to read a group of points every so often,
Starting Windows NT’sNetDDE Services
Using NetDDE requires NT’s NetDDE Services to be started. Windows NT Network DDE services are not automatically started. They must be set up and started.
You must have Windows NT administrator privileges to complete these procedures.
1. Launch the Control Panel. 2. Double-click the Services icon.
3. Scroll down the list box and select Network DDE. 4. Click the Startup button to display a Service dialog box.
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Optional: Click the Automatic radio button in the Startup Type section and click the OK button to return to the Services dialog box. This will cause NetDDE services to start automatically whenever NT starts.5. Click the Services dialog box Start button.
6. Scroll down the list box and select Network DDE DSDM. 7. Click the Startup button to display a Service dialog box.
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Optional: Click the Automatic radio button in the Startup Type section and click the OK button to return to the Services dialog box. This will cause NetDDE services to start automatically whenever NT starts.8. If Services is not already running, click the Services dialog box Start button. 9. Click the Close button to exit the Services dialog box and return to Control Panel.
You may close Control Panel as well.
Note: If the client machine is running in a Windows 95 environment, you must manually start NETDDE.EXE before using Network DDE.
Shared Topic Configuration:
With RSLinx, no user intervention is required to implement NetDDE. The only difference from the user’s point of view is in the Application/Topic/Item string that they enter in the client application to implement DDE communications with RSLinx (see the examples on the next page).
But behind the scenes, in order for a Server application on one Windows NT or 95 computer to use NetDDE to communicate with a Client application running on another computer, a DDE share must first be created on the Server computer.
Creating a Shared Topic in Windows NT:
Share entries are required in the Windows NT registry of the computer running the RSLinx Server for NetDDE to function. These shares must be created manually on the RSLinx Server using the DDESHARE utility that comes with NT.
1. Select the Run menu item to display a Run dialog box.
2. Type DDESHARE.EXE in the Command Line combo box. A DDE Shares window displays.
3. Select DDE Shares by double clicking the icon or select Shares menu item. A DDE Shares dialog box displays.
4. Click the Add a Share... button. A DDE Share Properties dialog box is displayed. 5. In the Share Name field, enter a name of your choice to remember this NetDDE
share by. The name should be one that identifies RSLinx and the specific PLC and data available through the RSLinx topic you wish to use.
6. Enter the Application and Topic within the Static fields. For RSLinx, the application is RSLINX and the RSLinx topic you wish to use.
7. Check Allow start application and click the OK button to return to the DDE Share Properties dialog box.
8. Highlight the DDE share name you just entered and click the Trust Share button to display a Trusted Share Properties dialog box.
9. Check both the Start Application Enable and Initiate to Application Enable check boxes.
10. Click the Set button then click the OK button to return to the DDE Shares dialog box. Close the DDE Shares dialog box.
Note: RSLinx does not automatically create a NetDDE share entry in the NT or Windows 95 registry for configured topics. While Windows NT currently has the tools to create shares manually, Windows 95 does not offer this utility. Rockwell Software is currently working on a utility to create DDE shares in a Windows 95 machine acting as a server.
Syntax:
The client setup for entering NetDDE syntax is similar to standard DDE syntax. The major additional piece of information is that you must identify the target computer where the server (e.g. RSLinx) resides, and instead of using the Application/Topic, you use the