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37 FUNCTIONS
37.1 System Switching
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 statuses of the CPU modules are the same.
Item New control system CPU module New standby system CPU module
Program
execution
Standard
program
Initial execution
type program
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 its head.
The program execution stops.
*1
Scan execution type
program
This type of program is executed from the step 0.
Fixed scan
execution type
program
The fixed scan execution interval is measured from 0. The program execution stops.
Standby type
program
This type of program is not executed.
Event execution
type program
• 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.
Safety
program
Fixed scan
execution type
program
The fixed scan execution interval is measured from 0.
Tracking transfer Tracking data is transferred to the new standby system. 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.
Online
change
Online
change
(ladder
block)
Standard program Write operation at system switching continues.
Safety program Safety programs cannot be changed online.
File batch
online
change
Standard program Write operation at system switching continues.
Safety program Safety programs cannot be changed online.
Device/label memory (standard label, safety
label, standard/safety shared label)
The state before system switching is held.
Signal flow memory
(standard/safety
program)
With tracking setting The signal flow of the old control system is reflected. The state before system switching is held.
Without tracking
setting
The signal flow of the tracking transfer targets is turned
on.
Setting the device/label initial value The values are not set.
Special relay (SM), special register (SD) The state before system switching is held.
However, when the CPU module is in the RUN state, SD520 to SD531 and SD1890 to SD1895 are cleared.
Safety special relay (SA\SM), safety special
register (SA\SD)
The state before system switching is held.
The safety special relay areas/safety special register areas related to safety communications (SA\SM1008,
SA\SM1016, SA\SM1024, SA\SM1032, SA\SM1040, SA\SM1048, SA\SM1056, SA\SM1064, SA\SM1088,
SA\SD1008 to SA\SD1071, SA\SD1088, SA\SD1089, SA\SD1090 to SA\SD1097, SA\SD1104 to
SA\SD1223, SA\SD1232 to SA\SD1359, and SA\SD1600 to SA\SD1663) are cleared.
Output (Y) The state before system switching is held. The state is held when the standby system
output setting of the redundant system
operation setting is enabled. If the setting is
disabled, the output (Y) is turned off and then
the output refresh stops.
Safety output device (SA\Y) The safety output device (SA\Y) is turned off
regardless of the standby system output setting.
Safety
output
CC-Link IE Field Network (CPU
module Master/local module)
After a safety program which is the fixed scan execution
type is operated using transferred device data, data is
output.
*2
Refresh processing is stopped because the
safety connection is disconnected.
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