26 REDUNDANT FUNCTION
26.2 System Switching
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26
Automatic system switching
When a redundant system is in backup mode, it judges whether system switching is required or not. Then, automatically
switches the systems between the control system and the standby system as required.
■System switching due to power-off, reset, or hardware failure of the CPU module
In a redundant system, the CPU module of the standby system monitors the status of the control system. If the control system
is unable to control the redundant system in the following cases, the CPU module of the standby system is switched to the
control system and the CPU of the new control system continues the control over the redundant system.
• The CPU module of the control system has been turned off.
• The CPU module of the control system has been reset.
• A hardware failure has occurred in the CPU module of the control system.
*1
*1 The CPU module of the control system is switched to the standby system even when the current standby system is not ready to switch.
( Page 381 Execution availability of system switching)
Operation when the CPU module of the control system (system A) is powered off
In a redundant system with redundant extension base unit or when a network is established using the CC-Link
IE Field Network module, systems are also switched in the following cases.
• When the redundant function module has been removed from the base unit
• When the base unit has failed
■Precautions when systems are switched by reset operation using the RUN/STOP/RESET
switch
When system systems are switched by reset operation using the RUN/STOP/RESET switch, the CPU module may be reset
after the operating status of the CPU module is switched to STOP. In this case, system switching is performed after the output
(Y) is turned off when the operating status is STOP. Therefore, when reset is performed using the RUN/STOP/RESET switch
of the CPU module in the control system while both systems are running, check that system switching after the output (Y) is
turned off does not cause a problem. If there is any problem, manually switch the control system to the standby system, and
then perform reset using the RUN/STOP/RESET switch.
Program executed
Power-off
System A
System B
System switching
Standby system
Program stopped
Program executed
Control system
Control system
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