Mitsubishi FXCPU have some special relay and register devices which are very useful for programming a Controller. these relay and register use full only for special purpose. in this article we discuss only special relay which are used in FXCPU. each special relay have reserved address you can't use special register address in general programming. for example M8000 is used for plc run mode if the plc in run mode this relay address set high. you can't use this relay for your programming it's reserved space in a memory. each special relay have a reserved address. relays device only have two state ON and Off(high or low).these relays also known as diagnostic relays. You can use these relays for Diagnostic purpose, Plc error, pulsed signal etc, controller information.

Mitsubishi Special Relay M8000

Mitsubishi Special Relay M8000 used to check plc is in run mode. if the plc is in run mode M8000 relay set to high(ON) otherwise M8000 is set to low. address of this relays is fixed.

in above program M8000 is set to 1 when Plc in run mode, if plc is not run mode than this register is set to low(Off).this help to identify plc mode.

Mitsubishi Special Relay M8001

Mitsubishi Special Relay M8001 used to check plc is in run mode. if the plc is in run mode than this relay set to low and if the plc is not run mode than is set to high.

in above program M8001 is set to 1 when Plc is in not run mode, if plc is in run mode than this relay is set to low(Off).

Mitsubishi Special Relay M8002

Mitsubishi Special Relay M8002 used for initialization pulse output. when controller is in run mode you can set this relay to 1 only for one program cycle. if the state of this relay is changed from high to low in a program cycle than this relay off for same program cycle it is set to high only once in a program cyle.

above is the example of Mitsubishi Special Relay M8002 in a program cycle this relay is set high but when this relay change state high to low in a same program cycle than output of this relay is unchanged.

Mitsubishi Special Relay M8004

Mitsubishi Special Relay M8004 is set to 1 if the plc have any error like logical, expression etc. this relay is help to identify plc error. address of this relays is M8004. this relay is also known as plc error relay.

above is the example of Mitsubishi Special Relay M8004, when the plc have in error than Y4 is set to high, otherwise M8004 is set to low. in this example we use division instruction when any error in division than M8004 is set to 1. for example if we divide 12 to 0 than M8004 is set high.

Mitsubishi Special Relay M8005

Mitsubishi Special Relay M8005 used to show battery status, if the controller battery is low than M8005 is set to high otherwise it set low. this help to know battery status of controller. M8005 relay also known as battery status relay identifier.

above is the example of Mitsubishi Special Relay M8005, output Y3 is set high. if the battery of controller is low than M8005 is set to high and output is also high.

Mitsubishi Special Relay M8013

Mitsubishi Special Relay M8013 is used to generate clock pulse for 1 sec, it will continue generate clock pulse until controller is on. M8013 is known as clock pulse generator relay.

above is the example of Mitsubishi Special Relay M8013, output Y13 is set to high for 1 second and off for 1 second. in this example we count a clock pulse by using counter as we know M8013 continue generate clock pulse. when counter value is equal to preset value than counter reset.

Mitsubishi Special Relay M8031

Mitsubishi Special Relay M8031 is used to clear all device relay which are not registered as battery latched. M8031 not affect data register. this help to clear all unlatched relay or register.

above is the example of Mitsubishi Special Relay M8031, in this example when M8031 is set to high than all all relay are set to low which are not latched to battery.in this Y000 is off because M8031 is set to High but condition for Y000 is true.

Mitsubishi Special Relay M8034

Mitsubishi Special Relay M8034 is used to disable all output but program execution is continue. M8034 is also known as off output relay. when M8034 is set to high than all output of program OFF condition but plc execute program continue.

above is the example of M8034 relay, all output is depend on rung input but if the M8031 is set to high than all output is off but program execution is continue. in this example timer T0 run continuously and set output y14 high when timer reached preset value but if the M8034 is set to high than output Y14 is off always.