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FX Series Programmable Controllers Devices in Detail 4
4-5
4.3.3 Special Diagnostic Auxiliary Relays
A PLC has a number of special auxiliary relays. These relays all have specific functions and
are classified into the following two types.
a) Using contacts of special auxiliary relays
- Coils are driven automatically by the PLC. Only the contacts of these coils may be
used by a user defined program.
Examples: M8000: RUN monitor (ON during run)
M8002: Initial pulse (Turned ON momentarily when PLC starts)
M8012: 100 msec clock pulse
b) Driving coils of special auxiliary relays
- A PLC executes a predetermined specific operation when these coils are driven by the
user.
Examples: M8033: All output statuses are retained when PLC operation is stopped
M8034: All outputs are disabled
M8039: The PLC operates under constant scan mode
4.3.4 Special Single Operation Pulse Relays
When used with the pulse contacts LDP, LDF, etc., M devices in the range M2800 to M3072
have a special meaning. With these devices, only the next pulse contact instruction after the
device coil is activated.
Available devices:
• Not all PLC’s share the same range, quantity or operational meaning of diagnostic
auxiliary relays. Please check the availability and function before using any device.
PLC specific diagnostic ranges and meanings are available in chapter 6.
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Turning ON X0 causes M0 to turn ON.
• Contacts , and are pulse con-
tacts and activate for 1 scan.
• Contact is a normal LD contact and
activates while M0 is ON.
Turning ON X0 causes M2800 to turn ON.
• Contact is a pulse contact and acti-
vates for 1 scan.
• Contacts and are pulse contacts
of the same M device as contact .
Contact has already operated, so
contact and do not operate.
• Contact is a normal LD contact and
activates while M2800 is ON.