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Relays
4.2
Relays
In your PLC programs you will often need to store intermediate binary results (a signal state of
"0" or "1") temporarily for future reference. The PLC has special memory cells available for this
purpose known as "auxiliary relays", or "relays" for short (device identifier: "M").
You can store the binary result of an operation in a relay, for example with an OUT instruction,
and then use the result in future operations. Relays help to make programs easier to read and
also reduce the number of program steps: You can store the results of operations that need to
be used more than once in a relay and then poll it is often as you like in the rest of the program.
M1
M1
In addition to normal relays the FX controllers also have retentive or "latched" relays. The nor-
mal unlatched relays are all reset to a signal state of "0" when the PLC power supply is switched
off, and this is also their standard state when the controller is switched on. In contrast to this,
latched relays retain their current states when the power is switched off and on again.
Device
Device identifier
Device type
Possible values für a device
Device address format
Number of devices and
addresses
You can also configure these relays as latched relays with the PLC parameters.
You can also configure these relays as unlatched relays with the PLC parameters.
If the optional battery is installed, the function of latched registers can be assigned to these registers in the PLC
parameters. They are then buffered by the battery.
4 – 4
Poll for signal state "1" (relay set)
Poll for signal state "0" (has the relay been reset?)
Unlatched relays
M
Bit device
0 or 1
Decimal
FX
384 (M0–M383)
1S
FX
384 (M0–M383)
1N
FX
2N
500 (M0–M499)
FX
2NC
FX
3G
384 (M0–M383)
FX
3GC
6144 (M1536–M7679)
FX
3GE
384 (M0–M383)
FX
3S
1024 (M512–M1535)
FX
3U
500 (M0–M499)
FX
3UC
M1
Relay types
Latched relays
128 (M384–M511)
1152 (M384–M1535)
524 (M500–M1023)
2048 (M1024–M3071)
1152 (M384–M1535)
128 (M384–M511)
524 (M500–M1023)
6656 (M1024–M7679)
MITSUBISHI ELECTRIC
Devices in Detail
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