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Allen-Bradley 1756-CNB - Condition Logic to Run after a Switchover; Example 1: Ladder Diagram

Allen-Bradley 1756-CNB
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Publication 1756-UM523F-EN-P - December 2006
Configure and Program the Controller 89
Condition Logic to Run After
a Switchover
You can condition a section of your logic to run after a switchover.
Follow these examples to create logic in preparation for a possible
switchover.
Example 1: Ladder Diagram
Get the ID of the primary chassis. That is always the chassis that runs the code.
Store the ID in the Chassis_ID_Now tag.
Chassis_ID_Now — DINT.
If this is the first scan then
Set the last value of the chassis ID = the ID of this chassis.
Chassis_ID_Last — DINT.
If the chassis ID changes, a switchover happened.
If a switchover occurs, then
1. Turn on the Switchover_Happened bit.
2. Set the last value of the chassis ID = the ID of this chassis.
Switchover_Happened — BOOL.
Continued on next page

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