Mitsubishi Electric MELSEC iQ-R Series User Manual page 170

Program example
The following shows a program example and the overview of the operation.
■Output of the control system (own system)
(0) The other system is notified of the start-up of the own system as the control system by turning on Y30 (Control system (own system)) using the direct access
output when the own system operates as the control system (SM1634 is on), or by turning off Y30 when the own system does not operate as the control
system.
After the automatic start-up, to enable the system switching, eliminate the cause of tracking communication
error and restart the CPU module in the standby system or in the state that waits for the other system to start.
11 BASIC CONCEPT OF REDUNDANT SYSTEM
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11.6 System Determination