Mitsubishi Electric MELSEC FX3U Programming Manual page 811

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
Special auxiliary relays
For efficiently creating SFC programs, it is necessary to use some special auxiliary relays. The table below
shows major ones.
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.
Operation of state relays and use of an output
two or more times
• In different state relays, a same output device (Y002 in
this example) can be programmed as shown in the right
figure.
In this case, when S21 or S22 is ON, Y002 is output.
However, if the same device as an output coil (Y002) in
a state relay is programmed in a ladder block program
or if a same output coil is programmed twice in one state
relay, it is handled in the same way as general double
coil.
Interlock of outputs
• In the state relay ON status transfer process, both
states turn ON only instantaneously (during one
operation cycle) at the same time.
Accordingly, between a pair of outputs which should not
be set to ON at the same time, provide an interlock
outside the PLC in conformance to the handy manual of
the PLC so that simultaneous ON can be prevented.
In addition, provide interlock in the program as shown in
the right figure.
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 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.
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.
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
20
21
22
Y002
20
Y001
21
Backward rotation
35.1 SFC Program
Y001
Y002
When S21 or
S22 is ON,
Y002 is output.
Y002
Y001
Forward
rotation
Y002
809
31
32
33
34
35
36
37
38
A
B