An OPC-DA Item Point is a connectivity point that represents an OPC Data Access (OPC-DA) item.
For operations listed below, following classes are used for the point itself, the operation parameters and operation arguments:
Operation | Point Type | Parameters Type | Arguments Type |
Read | DAItemPoint Class | DAItemPointReadParameters Class | DAItemPointReadArguments Class |
Subscribe | DAItemPointSubscribeParameters Class | DAItemPointSubscribeArguments Class | |
Write | DAItemPointWriteParameters Class | DAItemPointWriteArguments Class |
You can use following type aliases for this point type:
In order to describe the point and its subscription parameters, use the following sequence:
ServerDescriptorString, ItemId [, RequestedUpdateRate]
Where:
If the point or parameters differ from the default in other properties, the friendly topic syntax cannot be used.
The ServerDescriptorString may contain one of the following:
"OPCLabs.KitServer.2", "Demo.Ramp"
"OPCLabs.KitServer.2", "Demo.Ramp", "5000"
"opcda://MY-PC/OPCLabs.KitServer.2", "Demo.Single"
The XML topic syntax is capable to fully describe the point and parameters. It is currently not documented, and is subject to change.