There are no configured IOMs communicating on the I/O Link.  In other words, it 
appears to the primary controller that it has lost communication with the 
Secondary I/O Link interface. 
 
Both IOL channels connected to Primary and/or Secondary C300 I/O Link are lost 
 
Loss of input power to Secondary controller. 
 
Secondary controller failure. 
 
Removing the powered Secondary controller module from its IOTA. 
 
Conditions that do not result in loss of sync 
Assuming a synchronized or standby redundant controller pair, the following conditions 
do not result in loss of synchronization. 
 
Single FTE link to Primary and/or Secondary controller is lost. 
 
Single IOL channel connected to Primary and/or Secondary C300 I/O Link is lost. 
 
8.6 
Switchover 
A switchover describes the process where a Synchronized or Standby Secondary 
controller assumes the role of the Primary controller.  A switchover can be triggered 
immediately upon the detection of a fault in the Primary or upon the receipt of an  
operator command.  Depending on the switchover trigger, the original Primary controller 
attempts to reboot into the secondary role, but this controller is not immediately able to 
participate in another switchover operation.  Specifically, after the new secondary reboots 
into the secondary role, it must first perform and complete initial-synchronization before 
another switchover is allowed. 
 
Initiate Switchover - SWITCHCMD 
The Switchover command triggers a realistic switchover scenario. The original primary 
controller reboots into the secondary role and the Synchronized or Standby Secondary 
controller assumes the primary role to continue control operations. 
 
Max Switchover Time - RDNSOTIMEMAX 
The RDNSOTIMEMAX parameter indicates the maximum switchover time in 
milliseconds.  This is a high-water mark for all the previous switchover occurrences. 
This value is reset upon issuing the C300 Platform block's Stats Reset command.