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How to connect a device to Reliance via a DDE server

The now rather obsolete DDE is a standard for interprocess communication under Microsoft Windows. Data transfer is based on the client-server principle. The server is the so-called DDE server, which, for example, communicates with a device (devices) to acquire data and provides the data to DDE clients. The DDE client can be represented by the Reliance SCADA/HMI system.


See below for how to connect a device to Reliance via a DDE server:


  • First, it is essential to get and install the DDE server. DDE servers are usually supplied by their manufacturers.

  • Run the DDE server, create and register the so-called configuration. This means you have to define a list of devices with which the DDE server should communicate, specify how to communicate with these devices, configure the communication properties, and define tags (the so-called DDE Items) whose values are to be read from the devices. In some DDE servers, tags can be divided into groups. The so-called DDE topic (a unique identifier of a group within the DDE server) must be defined for each group. Do not forget to save and register the configuration so that this is available right after the startup of the DDE server.

    Note: Creating, saving, and registering a configuration is specific for each type of DDE server.

  • In the Reliance Design development environment's Device Manager, add a new device of type DDE (e.g., DDE1) and configure the DDE server property, which represents the name of the DDE server's exe file without the path and extension (for example, if C:\Program Files\MyDDEServer\MyDDEServer.exe is the DDE server, the property value will be MyDDEServer).

    Note: It is necessary to add a new device for each group of tags (DDE topic) defined in the DDE server configuration. If no groups have been defined, the entire DDE server configuration corresponds to a single device within the visualization project.

  • Add tags to the DDE1 device's Tags folder. For each tag, configure the DDE Item property according to the corresponding tag in the DDE server configuration.

  • In the Project Structure Manager, connect the DDE1 device (select the Devices folder of the computer on which the DDE server is to be run, choose the Connect Devices command from the popup menu, and select DDE1). Configure the DDE topic property according to the DDE server configuration. We recommend that the DDE server property, which, in this case, represents the name of the DDE server's exe file including the path and extension, be left blank and the DDE server be run separately before starting the visualization project. Otherwise, Reliance's runtime software will attempt to run the DDE server after loading the project. However, you may come across a situation when a connection with the DDE server cannot be established because the DDE server may not be fully initialized at that moment (e.g., it hasn't read its configuration yet).

  • Create visualization windows, add components to them (displays, buttons, etc.), and link the components to the DDE device's tags.

  • Run the DDE server.

  • Run the visualization project.

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