Mitsubishi Electric MELSEC iQ-R-R00CPU User Manual page 623

When the cable for the network module is disconnected
If a network module cable is disconnected, the systems may not be switched depending on the timing of error detection on the
control system and the timing on the standby system.
(1)
Control system
(1) When the control system detects cable disconnection first, the systems are switched.
(2) When the standby system detects cable disconnection first, the systems are not switched. At this time, a continuation error occurs on the control system
CPU module and the BACKUP LED flashes since a cause of the system switching failure has been generated.
In both case, replace the network module cable with a new one and clear the network error.
System switching during initial processing/initial processing (when switched to RUN)
When a system switching cause has been generated during initial processing or initial processing (when switched to RUN) on
the control system, the systems are switched after the initial processing or initial processing (when switched to RUN). Even if
the initial processing or initial processing (when switched to RUN) takes time and a communication error occurs, the systems
are switched after the initial processing or initial processing (when switched to RUN).
When a system switching cause has been generated during initial processing or initial processing (when switched to RUN) on
the standby system, whether the systems are switched or not depends on the system switching cause.
System switching cause
Power-off, reset, hardware failure of the CPU module
Stop error of the CPU module
System switching request from a network module
System switching request by the SP.CONTSW instruction
System switching request from the engineering tool
(2)
Standby system Other station systems
Whether to switch the systems
The systems are switched after the initial processing or initial processing
(when switched to RUN).
The systems are not switched.
37 FUNCTIONS
621
37.1 System Switching
37