Mitsubishi Electric MELSEC iQ-R Series User Manual page 423

Operation at system switching
The operation of a program executed in both systems differs at system switching. The following table summarizes the
operation at system switching.
Item
Program Initial execution type
execution program
Scan execution type
program
Direct access input (DX)
Direct access output (DY)
FROM/TO instructions
Instruction that requires several scans
For the operation at system switching as for programs which are not set as those executed in both systems, refer to the
following.
Page 380 Operation at system switching
CPU module of the new control system
When an initial execution type program has not been
completed in the old control system at system switching,
it is executed again from the start.
A scan execution type program is executed from the step 0.
Data is input when an instruction using the direct access input (DX) is executed in the program after system
switching.
However, no data is input for the direct input for the module mounted on the extension base unit.
Data is output when an instruction using the direct access output (DY) is executed in the program after system
switching. However, no data is output even when an instruction using the direct output of the module mounted on the
extension base unit is executed.
These instructions are executed when the instruction execution condition is satisfied in the program after system
switching.
However, when the FROM/TO instructions are executed for the module mounted on the extension base unit and
when the status of SM1762 (Operation setting for access from the standby system to the extension base unit) is set
to OFF, a stop error occurs. When the SM1762 status is set to ON, the operation is handled as non-processing.
(When "Continue" is selected in the operation error in the RAS setting for the CPU parameter, the error can be set as
a continuation error.)
• The instruction is executed when the instruction execution condition is satisfied in the program after system
switching.
• When the systems are switched while the instruction is being executed, the instruction execution continues and
the completion device turns on upon completion of the instruction execution.
CPU module of the new standby system
When an initial execution type program has not been
completed in the old standby system at system
switching, it is not executed in the new standby system
because the systems are switched after the program is
completed in the old standby system.
26 REDUNDANT FUNCTION
26.6 Program Execution in Both Systems
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