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Rockwell Automation 1756-RMxx ControlLogix Enhanced Redundancy System User Manual User Manual

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162

Rockwell Automation Publication 1756-UM535D-EN-P - November 2012

Chapter 7

Program the Redundant Controller

Bind Dependent Instructions with UID and UIE Instructions

If you cannot place scan-dependent instructions in the highest priority task,

consider using the User Interrupt Disable (UID) and User Interrupt Enable

(UIE) to prevent a higher priority task from interrupting the scan-dependent

logic.

For example, if you bind the scan-dependent logic previously shown, a higher

priority task would not interrupt the dependent instructions and a switchover

would not result in inconsistent data.

Figure 47 - Scan-dependent Instructions Bound with UID and UIE Instructions

For more information about UID and UIE instructions, see the Logix5000

Controllers General Instructions Reference Manual, publication

1756-RM003

.

UID and UIE keep

higher priority tasks

from interrupting

the logic.