Allen-Bradley 1756-CNB/E, User Manual

Page: 17 / 186

Publication 1756-UM523F-EN-P - December 2006
ControlLogix Redundancy System Overview 17
Controller Communication Terms
The 1757-SRM modules keep communication between the primary
and secondary chassis.
•
Unless you are updating controller revisions, do not download
the project to the secondary controller. While the secondary
controller is synchronizing with the primary controller, the
1757-SRM modules automatically let the primary controller
transfer the project to the secondary controller.
•
Once the secondary controller is synchronized, the 1757-SRM
modules keep the controller synchronized by providing the path
for crossloading any changes that occur in the primary
controller. These changes include:
– online edits.
– force values.
– changes to properties.
– changes to data.
– results of logic execution.
Term Description
Crossload The transfer of any or all of the contents of the primary
controller to the secondary controller. This could be updated
tag values, force values, online edits, or any other information
about the project. A crossload happens initially when the
chassis synchronize and then repeatedly as the primary
controller executes its logic.
Synchronize The process that readies a secondary chassis to take over
control if a failure occurs in the primary chassis. During
synchronization, the 1757-SRM modules check that the partner
modules in the redundant chassis pair are compatible with
each other. The SRM modules also provide the path for
crossloading (transferring) the content of the primary controller
to the secondary controller.
Synchronization occurs when power is applied to the secondary
chassis and after a switchover is diagnosed and fixed.
Synchronized The secondary chassis is ready to assume control if the primary
chassis fails.
Disqualified The secondary chassis is not synchronized with the primary
chassis. If a secondary chassis is disqualified, it cannot take
over control of the machine or process. A secondary chassis
can be manually disqualified.
Qualify Same as synchronize.
Qualified Same as synchronized.
1757-SRM Modules
Primary Chassis
43129
Secondary Chassis
Crossload