Mapping OPC Services to the IGUANA Gateway

[OPCXMLDA] defines several services that may be used to access underlying fieldbus data and retrieve status information. These services have to be mapped to appropriate ESD commands. This mapping will most often not be possible in a 1:1 translation as various OPC services will need multiple ESD commands. Other OPC concepts, such as subscriptions do not have suitable counterparts in the IGUANA gateway and have to be emulated in some way. However, the following OPC services may be directly mapped directly to ESD:

OPC Read:

This OPC service may directly be mapped to the ESD ``READ'' command. [OPCXMLDA] allows reading of multiple items at once. This can be implemented by subsequently requesting the according datapoint values through the ESD. Data conversion has to be implemented by the OPC Server as denoted above.

OPC Write:

Similar to the Read Service, an OPC ``Write'' can be mapped to the ESD ``WRITE'' command. As above, writing of multiple OPC items will be implemented by issuing multiple ESD ``WRITE'' commands.

OPC GetProperties:

This OPC service may be mapped to the ESD command ``DPINFO'', which will retrieve all available properties of a datapoint. In case the OPC server requests the properties of a fieldbus node, the command ``NODEINFO'' will be issued.