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4 SFC PROGRAM CONFIGURATION
MELSEC-Q
2) If the BRSET instruction is executed at an SFC program, block switching will be effective
only for the step currently being executed.
Even if the step in question is the same step, the BRSET instruction must be executed at
each block where the Sn and TRn instructions are used.
Moreover, within a single step, block switching will be effective from the point where the
BRSET instruction is executed to that step's processing END point.
When processing is repeated at the next scan following the processing END for that step,
the block in question will be designated as the “current block” until the point when the
BRSET instruction is executed again.
Block specified
by instruction
Block 0
END/0
A
Block specified
by instruction
ENDB
Block specified
by instruction
Current block
Block “n”
Block specified
by instruction
Current block
END
Block “n+1”
0
SFC programSequence program Sequence program
(Repeated)
1 scan
The block No. (m) designated by BLm\Sn or
BLm\TRn becomes valid regardless of whether this instruction is
executed or not.
When multiple steps are active at parallel branch, etc., only the step
where the instruction was executed will be valid.
When it is desired to designate blocks at multiple steps, the instruction
must be executed at each step.
Sn/TRn destination
block
Execution
Program
Instruction
executed
Instruction
executed
Instruction
executed
Instruction
executed
END processing
not performed
END processing
not performed
[Operation Error]
• Error No. 4621 occurs when the specified block does not exist or when the SFC program is in
the stand-by status.
[Program Examples]
(1) When X1 switches ON, the following program switches the Sn or TRn block number to the
block number stored at the D0 data register.
aX1
MOV Kn D0
BRSET D0
(2) When X2 switches ON, the following program switches the Sn or TRn block number according
to the constant at the Z1 index register.
aX2
BRSET K0Z1
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