Query Destination System
Use
The query destination system allows you to read current tag values from the source system of an agent instance or to write tag values to the source system of an agent instance. The agent instance can be the same agent instance from which the query destination system is called or another agent instance that is running on the same PCo computer.
You can define three types of queries:
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Retrieve query
A retrieve query reads values of tags from a source system and returns them to the caller of the query destination system.
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Store query
A store query writes values of tags to a source system and waits until the write operation is finished.
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Asynchronous store query
An asynchronous store query writes values of tags to a source system and does not wait until the write operation is finished.
Examples
Example 1: Your PCo agent instance provides an OPC UA method that reads a specific text file from a file system and returns the content of the file to the method caller.
Example 2: Your PCo agent instance provides an OPC UA method that sets the value of a tag in a Modbus source system.
Both examples show how PCo can be used for wrapping a variety of functions using OPC UA methods.