Table of Contents
FX
/FX
/FX
Series Programmable Controllers
3G
3U
3UC
Programming Manual - Basic & Applied Instruction Edition
Special auxiliary relays
For efficiently creating step ladder programs, it is necessary to use some special auxiliary relays. The table
below shows major ones.
The special auxiliary relays shown below are the same as those available in SFC programs.
Device
Name
number
M8000
RUN monitor
M8002
Initial pulse
STL transfer
M8040
disable
*1
STL state ON
M8046
Enable STL
*1
M8047
monitoring
*1.
Processed when END instruction is executed.
Block
A step ladder program is created as ladder circuits in the
same way as relay ladder. Accordingly, different from
SFC programs, it is not necessary to divide blocks for
relay ladder parts and SFC parts.
When there are ladder blocks and SFC blocks, put RET
instruction at the end of each step ladder program.
A PLC starts the step ladder processing by STL
instruction, and returns to the relay ladder processing
from the step ladder processing by RET instruction.
However, when consecutively programming a step
ladder in a different flow (when there is no relay ladder
before the step ladder in the different flow), RET
instruction between flows can be omitted, and RET
instruction can be programmed only at the end of the last
flow.
838
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.
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.
When this relay is set to ON, transfer of 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.
This relay automatically turns ON when any of the state 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.
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.
35 SFC Program and Step Ladder
Function and application
M8002
SET
Initial pulse
SET
STL
Y000
X000
SET
STL
Y001
X001
S0
RET
STL
Y002
X002
SET
STL
Y003
X003
S1
RET
END
35.2 Step Ladder
S0
Relay ladder
S1
Step ladder is
S0
started by STL
instruction.
S20
Step ladder
S20
It can be
omitted.
Step ladder is
finished by RET
instruction.
Step ladder is
S1
started by STL
instruction.
S30
Step ladder
S30
Step ladder is
finished by RET
instruction.
Relay ladder
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