Siemens SIMATIC PCS 7 OSx Operator's Manual page 37

SIMATIC PCS 7 OSx 4.1.2 Operator
Remote Data Transfer (RDT) Corresponding RDT programs on each
supervisory station execute approximately the same code at the same time.
If you attempt to do a role change while an RDT program is executing, the
role change fails if the RDT program fails to go idle during the role-change
wait period. In this event, wait a minute or two and then try the role change
again.
If you attempt to start an RDT program while a role change is in progress,
the program does not begin execution until after the role change is
complete.
You may observe some delay in the execution of an RDT program in the
Operate state when another OSx station is synchronizing. To see if this is
the cause of the delay, check Network Status, which shows when stations
are synchronizing. Program execution completes shortly after
synchronization finishes.
Batch BCL programs execute simultaneously on all supervisory stations.
Therefore, role changes do not adversely affect automated batch processing
for a system with more than one supervisory station. Consider these
additional guidelines.
• Since BCL programs are event driven, corresponding BCL programs on
each OSx station execute approximately the same code at all times.
• If a failover occurs, then BCL programs have approximately 10 seconds
to complete the event block that they are executing. After this, the role
change occurs and any database changes in the event block can be lost.
• If a manual role change takes place, then BCL programs have
approximately one minute to complete the event block that they are
executing. After this, the role change fails if any event blocks are still
executing.
• If the operator attempts to start a BCL program while a role change is
in progress, the program does not begin execution until after the role
change is complete.
You may observe some delay in the execution of a BCL program in the
Operate state when another OSx station is synchronizing. To see if this is
the cause of the delay, check Network Status, which shows when stations
are synchronizing. Program execution completes shortly after
synchronization finishes.
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OSx Station Basics