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29 PRECAUTIONS ON PROGRAMMING
29.1 Instructions Not Available in Redundant System
Re-execution of instruction when systems are switched during instruction execution
When the system switching is performed while an instruction that requires several scans is being executed, the instruction can
be executed again in the new control system after the system switching by using such as the following programs.
■REMFR instruction
When the system switching is performed while the instruction is being executed (M201 = ON), SM1643 (ON only in one scan
after system switching (standby to control)) will turn on for one scan in the new control system and the REMFR instruction will
be executed again on the station number 10 of the network number 1.
• DEVICES
*1 For details on the link special relays (SB) and link special registers (SW), refer to the manuals for the network used.
*2 Change the device number according to the system.
• Program example
DEVICES Data stored
SM1643 System switching check flag (standby system to control system)
SB47
*1
Baton pass status of own station
SW0A0.9
*1
Baton pass status of each station
M200
*2
On: Reading request
M201
*2
At instruction execution
M202
*2
ON at instruction re-execution request due to system switching
M203
*2
Completed without an error
M204
*2
Completed with an error
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