Dynamic Data Exchange.
WebAccess is a DDE Client and a DDE Server. The SCADA node is a DDE Server and DDE Client. WebAccess Clients can only trigger DDE commands to occur on the SCADA node.
Both DDE Server and DDE Clients act through the SCADA node. A script or keymacro running in a Web Browser will trigger the SCADA node to perform the DDE actions. For example, a script executes a command to read an EXCEL spreadsheet: the spreadsheet must be on the SCADA node and EXCEL must be running on the SCADA node, even if the command is executed by a Web Browser Client on a remote PC.
A 3rd party DDE Client application must have access to the WebAccess SCADA node: the DDE Client application must be running on the SCADA Node PC or have a Network DDE connection (NetDDE) to the SCADA node.
Similarly, WebAccess DDE Script commands and keymacro commands (which act as DDE Clients) must have access to the DDE Server they are reading or writing; the 3rd Party DDE Server application must be running on the SCADA Node PC or have a Network DDE connection (NetDDE) to the SCADA node.
Note that the DDE Server and DDE client is disabled without the Hardkey. You cannot test or train in simulation mode using DDE.
The bwDDE device driver (for an API COM Port) allows Tags to be read from a DDE Server. This allows 3rd Party Device Drivers to be used with WebAccess.