Rockwell Automation 1756-RMxx ControlLogix Enhanced Redundancy System User Manual - Manual (Page 183)

Rockwell Automation Publication 1756-UM535D-EN-P - November 2012 183
Program the Redundant Controller Chapter 7
• A PIO to a primary controller may fail if a switchover occurs while the
PIO is still in process.
When the anomaly occurs and the PIO fails, you may see any of these
errors:
– Failed to import file 'c\...\xxx.L5x
Object already exists
– Failed to import file 'c\...\xxx.L5x
Already in request mode/state
– CIP error: Problem with a semaphore
– Internal Object Identifier (IOI) destination unknown
After switchover is complete, re-attempt the PIO and it completes
successfully.
There are additional considerations necessary to performing online edits:
• Plan for Test Edits
• Reserve Memory for Tags and Logic
• Finalize Edits with Caution
Plan for Test Edits
Before you begin making edits to your redundant program while your system is
running, verify that the Retain Test Edits on Switchover setting meets your
application requirements.
If you enable the system to retain the test edits on a switchover (that is, you check
Retain Test Edits on Switchover), faults that result from the test edits can also
occur on the new primary controller after a switchover.
If you do not enable the system to retain the test edits on a switchover (that is,
you leave Retain Test Edits on Switchover unchecked), faults that result from the
test edits are not carried over to the new primary controller in the event of a
switchover.
IMPORTANT We recommend that you leave the Retain Test Edits on Switchover setting
at the default (that is, unchcecked) to avoid faulting both controllers when
testing your edits.