Mitsubishi Electric MELSEC iQ-R Series - Page 438

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26 REDUNDANT FUNCTION
26.11 Precautions on Programming
Instructions whose operations vary depending on tracking of the signal flow memory
The following describes the instructions whose operations after system switching vary depending on whether the signal flow
memory is tracked or not when the redundant system is in backup mode. The operations vary when one of the following
instructions is executed among program organization units that have the signal flow memory, memory to which tracking can
be performed.
■Rising instruction
If the system switching is performed without the signal flow memory being tracked, the signal flow memory of the new control
system turns on. Thus, a rising instruction whose execution condition turned on during system switching will not be executed.
■Falling instruction
If the system switching is performed without the signal flow memory being tracked, the signal flow memory of the new control
system turns on. Thus, a falling instruction whose execution condition turned off before the system switching will be executed.
■SCJ instruction
• When the signal flow memory is not tracked
Once the system switching is performed, the execution condition of the SCJ instruction turns on after the signal flow memory
of the new control system turns on. In the new control system, processing jumps to the pointer specified by the SCJ
instruction in the first scan.
Classification/type of special relay Instruction symbol
Rising instruction LDP, ANDP, ORP, LDPI, ANDPI, ORPI, PLS, MEP, EGP, SET F, RST F, FF, LEDR, DUTY,
LOGTRG, LOGTRGR, P (including MOVP and INCP), SP., JP., GP., ZP.
Falling instruction LDF, ANDF, ORF, LDFI, ANDFI, ORFI, PLF, MEF, EGF
SCJ instruction SCJ
Data processing instructions SORTD(_U), DSORTD(_U)
TIMCHK instruction TIMCHK
XCALL instruction XCALL
Rising instruction using SM1643 as an execution
condition

(1) After system switching, the processing jumps in the first and later scans.
ON
OFF
(1)
Execution condition of the SCJ
instruction
Jump by using the SCJ instruction
(old control system)
Jump by using the SCJ instruction
(new control system)
Jump
No jump
Jump
No jump
System switching start System switching completion
Systems are being switched.