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06/27/2023
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Can I subscribe to data changes from the HDA server in my HDA client? For example if I want to automatically get new data from the start timestamp to the present. I use C# and OpcNetApi.dll. By analogy in DA I can create subscription and subscribe to DataChanged event or create monitored item in UA with UA-.NETStandard libs.In the HDA specification, I found only such words in the section of asynchronous interfaces:
"It can ‘subscribe’ to data using the Async methods, which is more complex but very efficient. This is the recommended behavior for interactive clients because it will minimize display lockups. The client would be free to process other interactions while waiting for the data to return"
05/30/2017
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If you want current data then the DA interfaces are the only reliable way to get it.
HDA servers are usually distributed with DA servers that provide access to the same tags.
In some cases, the ItemIDs are the same for both servers. In others, there is a HDA method that provides the mapping to the DA itemIDs.
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