support wrote: - in DAReadItemArguments.ReadParameters. DAReadItemArguments are passed to EasyDAClient.ReadMultiple[Values].
- in some EasyDAClient.ReadItem[Value] overloads: they take DAReadParameters as an argument.

Thanks, did not find it in concepts, but I kinda figured it would be there since teh structure still existed. I will try it our.

support wrote: Note that use of Device reads (and especially Sync ones) is considered a bad practice in OPC.

Yes, but they are usefull if you want a responsive application.

How else would you ensure Device-initiated consistent transfer of multiple values?
- All data have time-stamps newer than Flag transfer-trigger or older by more than Age-value?

Can we in general be sure that OPC-reads/subscriptions of complex data-types (Arrays, strings etc) are atomic in nature or is this vendor-specific from Device to Device?

Hanssing

I the old days, there was a DeviceRead-method which could be used to ensure consistent, immediate and current datatrasfer:

This was changed in newer versions og the library.
How does one ensure consistent transfer of multiple items including the read-order in newer versions where this method has been removed?

Example:
PLC assigns data (In time-order) to ItemA, ItemB, ItemC, and afterwards signals New Data available in FlagD

OPC-application should read (in time-order) FlagD, ItemC, ItemB, ItemA
If FlagD is signalled, then data data allways contain consistent values.

If using subscription, then the application would have to wait a full agetime after seing the signal before data would be consistent. So the transfer-cycle is two times longer than it actually needs to be.

Can a reading of certain subscribed values be forced ?
Or can the behavior of DeviceReads be triggered somehow?

Regards
Hanssing