Mitsubishi Electric MELSEC Q Series Reference Manual page 436

(c) Program example
The following example program is written to the CPU module of station No.1.
• When the target station is not on a redundant system
• When the target station is on a redundant system
Confirm that the target station is on the control system, and execute the ZNRD instruction.
For execution of ZNRD instruction, provide an interlock using Redundant system
status (3) (SW01F0 to SW01F7) to ensure the target station is control system.
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Processing program for read completion
Processing program for normal completion
Processing program for error completion
Processing program for read completion
Processing program for normal completion
Processing program for error completion
Execution of ZNRD
instruction
Error code reading,
etc.
Execution of ZNRD
instruction
(when station No.3
is control system)
Execution of ZNRD
instruction
(when station No.4
is control system)
Error code reading,
etc.