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.
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