problems writing to variables/blocks on 800xA 6.0.3
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Read about Process Object Locking in the user's guides.
If "Operation Requires Locking" is enabled, lock must be taken before write is allowed.
Lock can be taken via faceplate's Lock Control (upper left corner) or by writing to the Global Properties Definition:ControlLockCommand OPC property found on all objects in System 800xA
OPC clients connecting via the out-of-proc and thus also DCOM compliant OPC DA Surrogate server (but not the regular in-proc running DA Server) can be exempted from the additional burden of lock handling by setting this registry key in the server hosting the surrogate:
0=Normal behavior (lock must be taken, if enabled)
1=Bypass locking (no need to take lock)
This way, it is possible to require lock for "humans" but not "robots".