4.10.7.3 Parent Component for Redundant Fieldbus

Fieldbus communication for redundant slaves is handled by a fieldbus and redundancy technology specific parent component, e.g. a specific COMM-DTM. All fieldbuses used to connect redundant slaves must be handled by one instance of such a parent component. In Scenario 2 for example, each fieldbus line is represented by an appropriate communication channel of the parent component. Therefore a Frame Application is able to use such a parent component without knowledge about the physical redundant fieldbus structure.

During a ValidateAddChild() and a OnAddChild() the parent component is able to detect if a Device-DTM to be added is able to handle redundancy by examining the parameter document of the instantiated DTM. In this case a specific address selection dialog within the parent component can be used. This address selection is fieldbus and redundancy specific. It's up to the parent component if redundancy is handled automatically or only after user interaction.

If the Frame Application has implemented the IDtmRedundancyEvents Interface the parent component has to inform the Frame Application about the redundant DTM by calling the OnAddedRedundantChild() method.

The parent component must be able to handle all possible communication paths to the redundant device. Within a SetParameter() call complete redundant address information can be provided to the DTM instance handling this redundant device. This DTM is then able to use this information to display all available communication paths. During a ConnectRequest() the DTM provides this complete address information to the parent component. The parent component is then able to select the currently active communication path. The communication path can be changed within the parent component without need for interaction with the Device-DTM.

A parent component may also be able to handle a DTM representing a not redundant field device. In this case this DTM is handled without using the redundancy specific information within FDT xml documents.