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MELSEC-Q
7 APPLICATION FUNCTIONS
7.11.3 System switching request function of control system
The control system includes the system switching request function, i.e., the master
module mounted in the control system CPU issues the system switching request to the
control system CPU when it detects the data link error such as link cable disconnection
or communication error. This function enables the standby system to continue the
control even when the master module of the control system goes down.
Multiplexed remote master station
Control system
Power
supply
QnPRHCPU
QJ71
LP21
Link cable
Multiplexed remote sub-master station
Standby system
System switching due to network error
Tracking cable
Error notice
A disconnection has occurred
Power
supply
QnPRHCPU
QJ71
LP21
Multiplexed remote master station
(sub-master operation)
Standby system
Power
supply
QnPRHCPU QJ71
LP21
Multiplexed remote sub-master station
(master operation)
Control system
Power
supply
QnPRHCPU QJ71
LP21
System B
System BSystem A
However, if the CPU of the control system cannot perform system switching due to the
standby system error, only the master operation of the master module shifts to the
master module of the standby system (multiplexed remote sub-master station).
In this case, since the CPU of the standby system cannot process the sequence
program, the CPU controls the network only. (Various modules mounted in remote I/O
stations cannot be controlled.)
Multiplexed remote master station
(sub-master operation)
Control system
Power
supply
QnPRHCPU
QJ71
LP21
Multiplexed remote sub-master station
(master operation)
Standby system
Power
supply
QnPRHCPU QJ71
LP21
System BSystem A
Under an error