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FX3G/FX3U/FX3UC Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
35 SFC Program and Step Ladder
35.1 SFC Program
31
FNC275-FNC279
Data
Transfer 3
32
FNC280-FNC289
High Speed
Processing 2
33
FNC290-FNC299
Extension File
Register
34
FNC300-FNC305
FX
3U
-CF-ADP
35
SFC•STL
Programming
36
Interrupt
Function
37
Special Device
38
Error Code
A
Version Up
Information
B
Execution Times
35.1.5 Latched (battery backed) type state relays
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.
35.1.6 Role of RET instruction
• 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.
35.1.7 Preliminary knowledge for creating SFC program
List of sequence instructions available in states
• 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.
Special auxiliary relays
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.
Instruction
State relay
LD/LDI/LDP/LDF,
AND/ANI/ANDP/ANDF,
OR/ORI/ORP/ORF,
INV,MEP/MEF,OUT,
SET/RST,PLS/PLF
ANB/ORB/MPS/MRD/
MPP
MC/MCR
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
Device
number
Name Function and application
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.