Use DDE (Dynamic Data Exchange)

Microsoft Windows DDE allows the continuous and automatic exchange of data between different Windows applications on the same machine without the need for any user intervention. For example, your company's Production group might use a spreadsheet application to graphically represent plant-floor data (product output). This could be dynamically updated with the latest live data using DDE to read values directly from Plant SCADA.

Note:
The DDE protocol has the following limitations:
• DDE is not designed for high-speed data transfer. It is only appropriate when data communication is not critical.
• You cannot use a DDE Server on a Plant SCADA computer that is running multiple processes.
• You cannot use a DDE Server on a Plant SCADA computer that is running in service mode.

Windows DDE uses the DDE protocol to send messages between applications that share data. Dynamic Data Exchange occurs between a DDE client application (which requests the data or service) and a DDE server application (which provides the data or service).

Note: Plant SCADA's DDE Server is disabled by default. To enable the DDE Server, set the parameter [DDE]Enable to 1 in the Citect.ini file. In addition, the Cicode function DDEPost is disabled on the DDE Server.

The DDE Client starts the exchange by establishing a conversation with the DDE server, and requesting data or services. The DDE server responds to these requests by providing the data or services to the DDE Client. The DDE Client terminates the conversation when it no longer needs the DDE server's data or services.

• For information about DDE conversations, see DDE Conversations and Client Syntax.

• To establish a DDE conversation between applications on the same computer, see Set up DDE Conversations.

• To establish DDE conversations between applications running on different computers over the same network, see Network DDE.

• To establish DDE Conversations with the Plant SCADA tag database directly, see Connect to the Tag Database using DDE.

Note: When reading or writing to Plant SCADA tags using DDE, you might unknowingly add to your Plant SCADA license point count. Once the dynamic point count is greater than the license point count, the software protection mechanism will terminate Plant SCADA runtime. Therefore, when accessing tags via DDE, it's important to remain aware of how many points you have used. For details, see Dynamic Point Count in the Installation and Configuration Guide.