Mitsubishi Electric MELSEC iQ-R Series User Manual page 389

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.
Control system (1)
(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 in the CPU module of the
control system and the BACKUP LED of the redundant function module flashes because a system switching disable cause exists.
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
*1 When the both systems are simultaneously turned on in a redundant system with redundant extension base unit, if a stop error occurs
during initial processing of the control system, the standby system also detects the stop error, and the system switching fails.
Extension cable errors in a redundant system with redundant extension base unit
■When the extension cable is redundant
When the extension cable between the main base module of the control system and the extension base unit or the extension
cable (on the active side) between extension base units fails or is disconnected, a bus access error occurs. After the systems
are switched due to a stop error, control is continued by the new control system.
■When the extension cable is not redundant
• When the extension cable between the main base module of the control system and the extension base unit fails or is
disconnected, a bus access error occurs. After the systems are switched due to a stop error, operation is continued by the
new control system.
• When the extension cable between the extension base units fails or is disconnected, a bus access error occurs, and the
systems are switched due to a stop error. A stop error also occurs in the new control system, and so control stops for both
systems.
Standby system (2) Other station systems
* 1
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.
• In backup mode, the systems are not switched.
• In separate mode, the systems will be switched after the initial processing or
initial processing (when switched to RUN).
26 REDUNDANT FUNCTION
26.2 System Switching
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