Mitsubishi Electric MELSEC iQ-R Series - Operation of a Program Executed in both Systems

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26 REDUNDANT FUNCTION
26.6 Program Execution in Both Systems
Operation of a program executed in both systems
The following table summarizes the operation of a program executed in both systems.
• To perform different diagnostic processing in the control system and the standby system by using a program
executed in both systems, use the special relay. SM1634 (Control system judgment flag) turns on only in the
control system and SM1635 (Standby system judgment flag) turns on only in the standby system. The
following is a program example that performs different processing by using the special relay. For the
processing (1) and (2), use the SET instruction or another instruction to prevent duplication of a coil in the
processing.
(1) Diagnostic processing in the control system, (2) Diagnostic processing in the standby system
• In a program executed in both systems, device/label values may differ between the control system and the
standby system. If the systems are switched in this state, the program is executed using the different data
and an unintended operation may be performed. To prevent this, the device/label values to be used can be
initialized by using SM1643 (ON for only one scan after system switching (standby system to control
system)) and SM1644 (ON for only one scan after system switching (control system to standby system)).
For the processing (1) and (2), use the SET instruction or another instruction to prevent duplication of a coil
in the processing.
(1) Initialization processing (standby system  control system), (2) Initialization processing (control system 
standby system)
System Backup mode Separate mode
Control system A program is executed according to its execution type. A program is executed according to its execution type regardless
of the setting in "Both Systems Program Executions Setting".
Standby system A program executed in both systems is executed according to its
execution type.
When an initial execution type program is set as a program
executed in both systems, the program is executed in the first scan
when the operating status of the CPU module is changed to RUN.
When an initial execution type program is not set as a program
executed in both systems, a scan execution type program that is
set as a program executed in both systems is executed in the first
scan when the operating status of the CPU module is changed to
RUN.
(1)
SM1634
(2)
SM1635
(1)
SM1643
(2)
SM1644