Mitsubishi MELSEC-Q Series Programming Manual page 98

4 SFC PROGRAM CONFIGURATION
POINTS
(1) Either of the following errors occurs if the SFC control instruction is executed from the
sequence program when the special relay for SFC program start/stop (SM321) is OFF.
• Instruction that specifies a block: BLOCK EXE. ERROR (error No.: 4621)
• Instruction that specifies a step: STEP EXE. ERROR (error No.: 4631)
(2) The SFC block (BL) and step relay (S) in the Basic model QCPU, High Performance model
QCPU, Process CPU, Redundant CPU, and Universal model QCPU (except for High-
speed Universal model QCPU) cannot be index-modified.
(3) The SFC block (BL) and step relay (S) in the High-speed Universal model QCPU can be
index-modified within the following range.
• BL0 to BL319 for the SFC block (BL)
• Range that is set in the Device tab of the PLC parameter dialog box for the step relay (S)
Note that the range will be S0 to S511 when the step relay (S) in SFC blocks is index-
modified.
(4) Do not use the SFC control instructions in interrupt programs or fixed scan execution type
programs.
If used, operation of the SFC program cannot be guaranteed.
(5) The step relay (S) can be used only in the following instructions.
• Step activation check instruction
• Active step batch read instruction
• Step START instruction
• Step END instruction
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