Siemens SIMATIC PCS 7 Function Manual page 193

Example: Failure of a fiber-optic cable
If a fiber-optic cable fails, the REDF LED and the IFM1F or IFM2F LED light up on the two
CPUs depending on the location of the fiber-optic cable failure. The H system goes to "Solo"
system mode and the user program continues to be processed by the master CPU used up
to this point (CPU0).
Example: Reintegration of the CPU in rack 1
Once the defective fiber-optic cable has been replaced and connected to both CPUs, you must
restart the backup CPU that is in STOP mode, i.e., CPU in Rack 1.
There are several options available to you:
● You have access to the automation system:
Turn the key switch on the failed CPU from its current position to STOP back to the setting
(RUN).
● You have an Ethernet connection to the H system:
In the "Operating Mode" dialog box, restart the CPU in Rack 1, which is in STOP mode.
– Open the PCS 7 project on an ES, click the "Online" icon in the task bar of SIMATIC
– Open the shortcut menu with a right click and open the "Operating Mode" dialog box
– Select the CPU in Rack 1 and click "Warm restart".
Fault-tolerant Process Control Systems (V8.1)
Function Manual, 11/2014, A5E34878832-AA
Manager and select a CPU in the right window pane.
with the menu command PLC > Operating Mode.
The CPU in Rack 1 links up again and performs an update. The system is then in
"Redundant" mode again.
Failure, Switchover and Return of Fault-tolerant Components
6.2 Automation system
193