450
28  FUNCTIONS
28.2  System Switching
■Special register
The following table shows the special register for system switching and the storage status of the CPU modules in the control 
system and standby system.
: Stored, : Not stored
*1 When the system switching has not been normally completed, a value is stored in this special register area of the control system.
CTRL LED and SBY LED of the redundant function module
System switching results can be checked with the CTRL LED and SBY LED on the front of the redundant function module.
SD 
number
Name Storage status at system switching
New control system 
CPU module
New standby system 
CPU module
SD1642 BACKUP/SEPARATE LED flashing cause 
SD1643 System switching cause 
SD1644 Cause of the system switching failure
*1
SD1645 System switching request status from a network module of own system 
SD1646 System switching request status from a network module of the other system 
SD1648 Cause of the other system monitoring error 
SD1649 System switching Cause (when the systems are successfully switched) 
SD1650 System switching instruction ID number 
Switching from the standby system to the control system Switching from the control system to the standby system