Auxiliary Relay [M]; Numbers Of Auxiliary Relays; Functions And Operation Examples - Mitsubishi Electric MELSEC FX3U Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
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. FX /FX PLC
3U 3UC
General type
M0 to M499
500 points
2. FX PLCs
3G
General type
M0 to M383
384 points
*1. This area is not latched (battery backed). It can be changed to a latched (battery backed) area by
setting the parameters.
*2. This area is latched (battery backed). It can be changed to a non-latched (non-battery-backed) area
by setting the parameters.
*3. The characteristics of latch (battery backup) cannot be changed in the parameters.
*4. 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.
When simple N : N link or parallel link is used, some auxiliary relays are occupied for the link.
4.3.2

Functions and operation examples

1. General type
M100
NO contact
M100
NC contact
Auxiliary relay circuit
92
latched (battery
backed) type
M500 to M1023
*1 *2
524 points
Fixed latched
(EEPROM keep) type
M384 to M1535
1152 points
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
M100
required in control, use latched (battery backed) type auxiliary relays.
Fixed latched (battery
backed) type
M1024 to M7679
*3
6656 points
General type
M1536 to M7679
*4
6144 points
→ Refer to the Data Communication Edition manual.
4 Devices in Detail
4.3 Auxiliary Relay [M]
Special type
M8000 to M8511
512 points
Special type
M8000 to M8511
512 points