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37 FUNCTIONS
37.5 Program Execution in Both Systems
To enable the output (Y) from a standby system external device using a program executed in both systems,
configure settings in "Standby System Output Setting" of the CPU parameter. ( Page 652 Redundant
System Operation Setting)
Operation of a program executed in both systems
The following table shows the operation of a program executed in both systems.
• To perform different diagnostic processing in the control system and 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) only in the standby system. The following
shows a program example of when different processing is performed. For (1) and (2) in the following
example, use the SET instruction or others to prevent duplication of a coil in the processing.
(1) Diagnostic processing in the control system, (2) Diagnostic processing in the standby system
• When a program executed in both systems is used, device/label values may differ between the control
system and the standby system. If the systems are switched in this state, the program is started based on
the different data, causing an unintended operation. 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 (1) and (2)
in the following example, use the SET instruction or others to prevent duplication of a coil in the processing.
(1) Initialization processing (standby system control system), (2) Initialization processing (control system
standby system)
Control system/
Standby system
Operation
Control system A program is executed according to its execution type.
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
while the CPU modules are in the RUN state.
When an initial execution type program is not set as a program executed in both systems, a program executed in both systems of
scan execution type is executed in the first scan while the CPU modules are in the RUN state.
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