Operation At System Switching - Mitsubishi Electric MELSEC iQ-R Series User Manual

Operation at system switching

The following table shows the operations of the CPU modules of when the control system and the standby system are
switched.
These operations are for when both systems are operating and the operating status of the CPU modules are the same.
Item
Program Initial execution
execution type program
(except the SFC
program)
Scan execution
type program
Fixed scan
execution type
program
Standby type
program
Event execution
type program
Execution of SFC Block active
program status
Step active status
Execution of
action
Tracking transfer
Online change
Device/label memory
Signal flow memory
( Page 396 Tracking transfer
setting for the signal flow memory)
Special relay (SM), special register
(SD)
Output (Y)
Direct access input (DX)
Direct access output (DY)
FROM/TO instructions
Instruction that requires several scans
Constant scan
*1 The operation varies in a program executed in both systems. ( Page 421 Operation at system switching)
*2 The operation varies when the signal flow memory is not transferred. ( Page 436 Instructions whose operations vary depending on
tracking of the signal flow memory)
*3 The operation varies when the standby system output setting is enabled. ( Page 425 Redundant System Operation Setting)
26 REDUNDANT FUNCTION
380
26.2 System Switching
CPU module of the new control system
This type of program is not executed.
However, when an initial execution type program has
not been completed on the old control system at system
switching, it is executed again from the start.
This type of program is executed from the step 0.
The fixed scan execution interval is measured from 0.
This type of program is not executed.
• Interrupt program: The program is executed when an
interrupt factor is generated.
• ON of bit data (TRUE): The program is executed
when a specified factor is generated.
• Passing time: A specified time is measured from 0.
The status before system switching is held.
The status before system switching is held.
The program execution is started in the active action
using transferred device data.
Tracking data is transferred to the new standby system.
Write operation at system switching continues.
The state before system switching is held.
• In backup mode, the signal flow of the old control
*2
system is reflected.
• In separate mode, the signal flow of the old standby
system is reflected.
The state before system switching is held.
However, when the CPU module is in the RUN state, SD520 to SD531 are cleared.
The state before system switching is held and output
refresh is performed.
Data is input when an instruction using the direct access
input (DX) is executed in the program after system
switching.
Data is output when an instruction using the direct
access output (DY) is executed in the program after
system switching.
These instructions are executed when the instruction
execution condition is satisfied in the program after
system switching.
These instructions are executed when the instruction
execution condition is satisfied in the program after
system switching.
Constant scan is enabled.
CPU module of the new standby system
*1
The program execution stops.
The program execution stops.
The program execution stops.
Tracking data is received. However, when a stop error
occurs on the new standby system, the new standby
system does not receive the tracking data.
The state before system switching is held.
After the output (Y) is turned off, output refresh stops.
No operation is performed because the program does not
*1
operate.
• No operation is performed because the program does
*1
not operate.
• When the systems are switched while the instruction is
being executed, the instruction execution continues.
However, the completion device does not turn on in the
new standby system, and it turns on in the control
system after the next system switching.
• The constant scan function is disabled in backup mode.
• The constant scan function is enabled in separate mode.
*3
*1