ABB AC 800M

Automatic Switch-Over to Backup CPU Section 4 Operation
114 3BSE 027 941 R301
Automatic Switch-Over to Backup CPU
In a redundant configuration an automatic switch-over from the Primary CPU to the
Backup CPU occurs in the following situations, provided they are in synchronized
state (DUAL LED is lit):
• Memory error in the Primary CPU.
• Other HW-error in the Primary CPU, which causes CPU crash.
• Severe communication errors on the Control network i.e loss of both network
ports in the Primary CPU.
• Severe communication errors on the ModuleBus (if ModuleBus is part of the
HW configuration) i.e. loss of clusters in the Primary CPU .
Note that a Backup CPU with severe communication errors on the ModuleBus
will be rejected (if ModuleBus is part of the HW configuration) and
synchronized state will never be reached as long as error remains.