35 BASIC CONCEPT
35.8 Determination of Control System/Standby System
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35
When starting up the previous control system as the control
system
The system A is always specified as the control system when both systems are started up simultaneously. Even though both
systems are temporarily powered off due to a power failure or other causes while the system B is operating as the control
system, the system A is started up as the control system when both systems are powered on again.
To start up the system B that was the previous control system as the control system again, create a program that uses
SM1636 (Previous control system identification flag). For a system where a network module has been mounted, execute the
SP.CONTSW instruction after a network module on the other system is started up.
Program example
Executing a system switching instruction when the CPU module in the system A is set to the RUN state for the first time
switches the system B to the control system. Turn on SM1646 (System switching by a user) in advance.
Operation example
1. Both systems are temporarily
powered off due to a power failure
or other causes while the system B
is operating as the control system.
2. The system A is started as the
control system when both systems
are powered on. SM1636 turns on
for only one scan after the CPU
module in the system A is set to the
RUN state.
3. The system switching is performed
by the SP.CONTSW instruction.
4. The system B is switched from a
standby system to a control system.
System A
Standby system → Power-off
System B
Control system → Power-off
GOEND
SP.CONTSW D0 M0
SM1636
GOEND
SP.CONTSW D0 M0
SM1636
System A
Power-on → Control system
System B
Power-on → Standby system
System switching
System A
Control system
System B
Standby system
System A
Control system → Standby system
System B
Standby system → Control system
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