19.5.DDE

This option in the Properties Window sets up the OPC DataHub to act as a DDE client and/or DDE Server for DDEAdvise messages. For more information on DDE, please refer to Section17.3.3, “DDE Protocol” and AppendixG, DDE Overview.

DDE Client

To act as a DDE client, check the Act as a DDE client box.

[Important]

For best performance, ensure that a DDE server is running when using the DataHub as a DDE client. A DDE client can consume substantial system resources trying to connect if a DDE server is not available.

To add a new service or topic, press the Add button. To edit a service/topic, double-click it or select it and press the Edit. To remove a service/topic, select it and press the Remove button.

Double-click a selection, or pressing the Add or Edit button opens the DDE Item Definition Window:

Here is what must be entered:

Connection Name

A name used by the OPC DataHub to identify the connection. There should be no spaces in the name. It doesn't matter what name is chosen, but it should be unique to other connection names. Each connection can have only one Service and one Topic, but it can have multiple Items.

Service

The service name of the DDE server to this client.

Topic

The DDE topic under which the data will be sent.

Item Names

The DDE item name, which corresponds to a point name in the OPC DataHub. If that point doesn't exist in the DataHub, it will be created. Enter a name for each item and press the Add button to add items. To remove an item, highlight it and press the Remove button. Once all the information is entered correctly, press the OK button to enter the definition.

DDE Server

To have the OPC DataHub act as a DDE server, check the Act as a DDE server box. The default service name is datahub.

To add a DDE service name to the list, click the Add button and enter the name in the DDE Service Window:

To edit a DDE service name, double-click it or select it and press the Edit. To remove a DDE service name, select it and press the Remove button.

[Note]

It is currently possible to have more than one instance of the OPC DataHub, with one or more DDE service names in common, running on a single machine. If you plan to configure a system like this, you should ensure that each instance of the DataHub has unique data domain names. Otherwise, when any two of those DataHubs are acting as servers, it is not possible to predict which one of them a given client will send data to.

Non-English Characters in Excel

Excel uses a DDE transmission format called XlTable or Fast Table Format when transmitting data via DDE. Using this format results in a huge speed-up in DDE transmission from Excel to the OPC DataHub. Unfortunately, this format does not support non-ASCII characters in strings for DDEPoke and DDEExecute commands, which are commonly used in Excel macros. These commands can only transmit English words under XlTable format.

The Accept non-English characters in Excel strings (slower) button forces Excel to avoid the XlTable format and allows you to transmit strings in Unicode.