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App-120

Appendix 3  SPECIAL RELAY LIST

Special relays, SM, are internal relays whose applications are fixed in the Programmable 
Controller.

For this reason, they cannot be used by sequence programs in the same way as the normal 
internal relays.

However, they can be turned ON or OFF as needed in order to control the CPU module.

The heading descriptions in the following special relay lists are shown in 3.1.

For details on the following items, refer to the following manuals:
 • Networks

Manual of the corresponding network module

 • SFC

QCPU(Q mode)/QnACPU Programming Manual (SFC)

Do not change the values of special relays set by the system with user program or 
device test operations.
Doing so may result in system downtime or communication fault.

TableApp.3.1 Explanation of special relay list

Number

• Indicates special register number

Name

• Indicates name of special relay

Meaning

• Indicates contents of special relay

Explanation

• Discusses contents of special relay in more detail

Set by 
(When set)

• Indicates whether the relay is set by the system or user, and, if it is set by the system, when setting is performed.

<Set by>
  S

: Set by system

  U

: Set by user (sequence programs or test operations from GX Developer)

  S/U

: Set by both system and user

<When set>
  Indicated only for registers set by system
  Each END

: Set during each END processing

  Initial

: Set only during initial processing (when power supply is turned ON, or when going from STOP 

to RUN)

  Status change

: Set only when there is a change in status

  Error

: Set when error occurs

  Instruction execution : Set when instruction is executed
  Request

: Set only when there is a user request (through SM, etc.)

  System switching

: Set when system switching is executed.

Corresponding 

ACPU M9

• Indicates the corresponding special relay (M9

) of the ACPU.

 (When the contents are changed, the special relay is represented M9

 format change. Incompatible with the 

Q00J/Q00/Q01 and QnPRH.)

• New indicates the special relay newly added to the Q series CPU module.

Corresponding 
CPU

Indicates the corresponding CPU module type name.
QCPU

: Indicates all the Q series CPU modules.

Q00J/Q00/Q01

: Indicates the Basic model QCPU.

Qn(H)

: Indicates the High Performance model QCPU.

QnPH

: Indicates the Process CPU.

QnPRH

: Indicates the Redundant CPU.

QnU

: Indicates the Universal model QCPU

Each CPU module model name: Indicates the relevant specific CPU module. (Example: Q02U)