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FX

3G

/FX

3U

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3UC

 Series Programmable Controllers

Programming Manual - Basic & Applied Instruction Edition

35 SFC Program and Step Ladder

FN

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275
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27

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Trans
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FN

C

280-
FN

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289

H

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Pr

ocessing 2

FN

C

290-
FN

C

299

E

xtension Fi

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R

egister

FN

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300-
FN

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30

5

FX

3U

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F-A

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SFC•

STL

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In the latched (battery backed) type state relays, the ON/OFF status is backed up by the battery or EEPROM memory
against power failure.
Use this type of state relays if the operation should be restarted from the last point at power recovery after power
failure occurred in the middle of machine operations.

• Use RET instruction at the end of an SFC program.

When inputting an SFC program using GX Developer, however, it is not necessary to input RET instruction 
(because RET instruction is automatically written).

• In a PLC, two or more SFC blocks can be put between step 0 and the END instruction.

When there are ladder blocks and SFC blocks, put RET instruction at the end of each SFC program.

• STL instruction cannot be used in interrupt programs and subroutine programs.
• When using SFC programs (STL instruction), do not drive state relays S using SET or OUT instructions in an 

interrupt program.

• It is not prohibited to use jump instructions in state relays.  However, it is not recommended to use jump instructions 

because complicated movements will result.

*1.

The MPS instruction cannot be used immediately after a state relay (STL instruction), even in a drive
processing circuit.

For efficiently creating SFC programs, it is necessary to use some special auxiliary relays.  The table below shows
major ones.

*1.

Processed when END instruction is executed.

Initial/general state relay

Available

Available

*1

Not available

Branch/recombination
state relay

Drive processing

Available

Available

*1

Not available

Transfer processing

Available

Not available

Not available

M8000

RUN monitor

This relay is normally ON while the PLC is in the RUN mode.
Use this relay as the program input condition requiring the normally driven status or for indicating the PLC
operation status.

M8002

Initial pulse

This relay turns ON and remains ON only instantaneously when the PLC mode is changed from STOP to
RUN.
Use this relay for the initial setting of a program or for setting the initial state relay.

M8040

STL transfer 
disable

When this relay is set to ON, transfer to the ON status is disabled among all state relays.
Because programs in state relays are operating even in the transfer disabled status, output coils do not
turn OFF automatically.

M8046

*1

STL state ON

This relay automatically turns ON when any of state the relays S0 to S899 or S1000 to S4095 turn ON. 
Use this relay to prevent simultaneous startup of another flow or as a process ON/OFF flag.

M8047

*1

Enable STL 
monitoring

When this relay is driven, the device number of a state relay in the ON status having the smallest device
number among S0 to S899 and S1000 to S4095 is stored to D8040, and the state relay number in the ON
status having the next smallest device number is stored to D8041.  In this way, up to eight state relays in
the ON status are stored up to D8047.
•

In the FX-PCS/WIN(-E), FX-30P, FX-20P(-E), and FX-10P(-E), when this relay is driven, the state
relays in the ON status are automatically read and displayed.
For details, refer to the manual of each peripheral equipment.

•

In the SFC monitor in GX Developer, the automatic scroll monitoring function is valid even if this relay is
not driven.