Rockwell Automation 1785-CHBM ControlNet PLC-5 Hot Backup System User Manual - Manual (Page 94)

Publication 1785-UM024B-EN-P - January 2003
B-14 Backup States
If you selected the Designated Primary feature, and the odd
node of the odd-even backup pair has just gone through
secondary qualification, a switchover automatically occurs.
The odd node becomes the primary system, and the even node
transitions from the primary system to the secondary system.
The even node’s transition from primary to secondary happens
immediately. The even node does not go through qualification
when it becomes the secondary system.
Reasons for Qualification Major Fault
While qualification should complete without any problems, there are
several checks performed during qualification that can cause it to fail.
When the qualification procedure fails, a major fault is declared.
Qualification could fail under any of the following circumstances or
conditions:
• Failure of the Qualification Data Table crossload
• Failure of the Qualification State Data Table crossload
• Failure of the Equivalence Check
• The occurrence of an unrelated major fault in the PLC-5 system
during qualification
• Movement of the keyswitch to Program mode during
qualification
• Inability to retrieve the Edit Resource at the beginning of
qualification
• Presence of one or more invalid backup configuration
parameters
• A change in the primary status of the partner PLC-5 processor
(i.e., either the partner PLC-5 processor became primary during
qualification, or the partner PLC-5 went from primary to
non-primary during qualification).
• The ControlNet backup state was Invalid backup state.
Refer to Chapter 5 (Troubleshooting) for information on fixing a
Qualification major fault.
Switchover
Switchover occurs when one of the processors of the PLC-5
ControlNet backup system transitions from the Secondary backup
state to the Primary backup state. The new primary processor gains
control of the system outputs on the ControlNet channel; the old
primary processor loses control.