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Is it possible to request a subscription of a specific item to a OPC Server using the JEasyOpc library? Using async20Read(Group group) will only subscribe the group to the OPC Server in such a way, that after an event happened all items belonging to the group have to be downloaded at the client side. This costs lots of bandwidth having thousands of items which have to be downloaded if one item drops an event!

Yannick Wald
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I haven't used JEasyOPC, but the OPC specification states that AsyncIO::Read and AsyncIO2::Read accepts a list of items that you want to read from the server. This allows you to specify exactly how many and which items' values are to be sent in an update.

Ken
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  • this is also what i understood from the specification. I didn't find a way in JEasyOpc to register specific items to the server for polling for events.. and i can't even examine how the methods are actually working since the most important part is implemented in a delphi dll, i guess. – Yannick Wald Sep 05 '12 at 15:50
  • you could create short-lived groups when needed that have only the desired items in them...and then perform a Read on those groups. – Ken Sep 05 '12 at 16:32
  • yes i could.. but according to the code the asynch method calls a getDownload() method in a loop.. looks like it is wrong implemented, actually the server have to call the client's method. i changed to utgard, it is relying on a java-dcom bridge and does not depend on the OS (for the client at least). – Yannick Wald Sep 07 '12 at 11:47