From OpenSCADAWiki
To acquire data by the ModBus protocol in OpenSCADA, there the ModBus module of the subsystem "Data Acquisition" is provided. To add a new controller object in the configurator, open the module page ModBus "Start"->"Data Acquisition"->"Module"->"ModBus" and press "Add" in the "ModBus" item's context menu (Fig.4.1.1).