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FX3S/FX3G/FX3GC/FX3U/FX3UC Series
Programming Manual - Basic & Applied Instruction Edition
4 Devices in Detail
4.3 Auxiliary Relay [M]
4.3 Auxiliary Relay [M]
There are many auxiliary relays inside the PLC. Coils of auxiliary relays are driven by contacts of various devices
inside the PLC in the same way as output relays.
Auxiliary relays have many electronically NO contacts and NC contacts which can be used arbitrarily inside the PLC.
However, external loads cannot be driven directly by these contacts. External loads should be driven by output relays.
4.3.1 Numbers of auxiliary relays
The table below shows auxiliary relay (M) numbers. (Numbers are assigned in decimal.)
1. FX3S PLC
2. FX
3G/FX3GC PLCs
3. FX
3U/FX3UC PLCs
*1. These registers can be changed to the latched (battery backed) type by the parameter setting when the
optional battery is used. However, the latched range cannot be set.
*2. This area is not latched (battery backed). It can be changed to a latched (battery backed) area by setting the
parameters.
*3. This area is latched (battery backed). It can be changed to a non-latched (non-battery-backed) area by setting
the parameters.
*4. The characteristics of latch (battery backup) cannot be changed in the parameters.
When N : N Network or parallel link is used, some auxiliary relays are occupied for the link.
→ Refer to the Data Communication Edition manual.
4.3.2 Functions and operation examples
1. General type
All of general type auxiliary relays turn OFF when the PLC turns OFF.
When the ON/OFF status of auxiliary relays just before power failure is
required in control, use latched (battery backed) type auxiliary relays.
General type
Fixed latched
(EEPROM keep) type
General type Special type
M0 to M383
384 points
M384 to M511
128 points
M512 to M1535
1024 points
M8000 to M8511
512 points
General type
Fixed latched
(EEPROM keep) type
General type Special type
M0 to M383
384 points
M384 to M1535
1152 points
M1536 to M7679
6144 points
*1
M8000 to M8511
512 points
General type
Latched
(battery backed) type
Fixed latched
(battery backed) type
Special type
M0 to M499
500 points
*2
M500 to M1023
524 points
*3
M1024 to M7679
6656 points
*4
M8000 to M8511
512 points
M100
M100
M100
NO contact
NC contact
Auxiliary relay circuit