Rockwell Automation 1756-RMxx ControlLogix Enhanced Redundancy System User Manual - Manual (Page 161)

Rockwell Automation Publication 1756-UM535D-EN-P - November 2012 161
Program the Redundant Controller Chapter 7
For example, if a higher priority task interrupts the logic shown in this example,
the value of scan_count.ACC is sent to the secondary controller at the end of the
program in the higher priority task. If a switchover occurs before the primary
controller completes the EQU instruction, the new primary controller starts its
execution at the beginning of the program and the EQU instruction misses the
last value of scan_count.ACC. As a result, any programming that uses the
Scan_Count_Light tag may also execute by using incorrect data.
Table 25 - Scan-dependent Logic
Interrupt by higher
priority task.
Switchover