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Rockwell Automation Publication 1756-UM540E-EN-P - December 2017
Chapter 5
1756-OF8I Isolated Analog Output Module
You can use Produced/Consumed tags for synchronization; however, the
Redundant Owner Input tags provide the majority of information needed for
synchronization.
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After both controllers decide it is safe, the primary controller sets Claim.
•
After the secondary controller sees that the primary controller has taken
ownership, the secondary controller sets Ready.
•
The secondary controller monitors the I/O and the other controller to
determine the current owner.
•
If the secondary controller becomes the owner, it can set its Claim bit to
take or hold ownership, or can just maintain Ready.
•
Once the primary controller comes back and is in Run mode, that
controller toggles its Claim bit, and the I/O switches back to that
controller.
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A “S:FS” XIC should be used to disable Claim/Ready bits until the
controller has entered Run mode and can evaluate if it should make a
Claim or Ready transition.
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Failure to do this could lead to a ‘claim’ happening before the controller
is back in Run mode. Thus, the output would transition briefly to its
Program Mode Safe State prior to entering Run mode rather than
making a smooth transition from secondary controller back to primary
controller.
•
When the secondary controller sees that the primary controller has
retaken ownership, it clears its Claim bit and goes back to Ready.
•
Monitor for Connection Loss on controller. Add GSV to monitor
connection status and clear Claim and Ready flags on Connection Loss to
prevent undesired behavior when connection is restored.
•
Monitor for Major Fault on controller. Optionally, add Fault Routine to
clear Claim and Ready owner flags if Major Fault is not to be cleared in
faulted controller to allow secondary controller to take immediate control.
