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Appendix 3 Special Relay (SM) for MELSECNET/H
(MELSECNET/10 Mode) Remote I/O Station
The special relay (SM) is an internal relay whose specification is fixed in the programmable controller. For this reason,
the special relay cannot be used in the same way as other internal relays used in sequence programs. However, the bit
of the special relay can be turned on or off as needed to control the CPU module or the MELSECNET/H remote I/O
module. To monitor and turn on or off the bit of the special relay of the MELSECNET/H remote I/O module, use GX
Developer. Connect GX Developer to the remote master station or the MELSECNET/H (MELSECNET/10 mode)
remote I/O station to perform monitoring and device tests.
The list in this section provides only the special relay areas related to the MELSECNET/H remote I/O module. The
following table shows how to read the special relay list.
For details on the following items, refer to the following.
• For CPU related items: User's manual for the CPU module used
• For network related items: Manuals for each network module
• For SFC programs: MELSEC-Q/L/QnA Programming Manual (SFC)
Item Description
No. Special relay number
Name Special relay name
Meaning Description of special relay
Explanation Detailed description of special relay
Set by
(When Set)
Set side and set timing of special relay
<Set by>
• S: Set by system
• U: Set by user (using a sequence program or test operation by a peripheral)
• S/U: Set by both system and user
<When Set>
The following shows the set timing when the special register is set by system.
• Every END processing: Set during every END processing
• Initial: Set during initial processing (after power-on or status change from STOP to RUN)
• Status change: Set when the operating status is changed
• Error: Set if an error occurs
• Instruction execution: Set when an instruction is executed
• Request: Set when requested by a user (using the special relay)
• When system is switched: Set when the system is switched (between the control system and the standby
system)
Corresponding ACPU
M9
• Special relay (M9) supported by the ACPU ("M9 format change" indicates the one whose
application has been changed. Incompatible with the Basic model QCPU and Redundant CPU.)
• "New" indicates the one added for the QCPU or QnACPU.
Corresponding CPU
CPU module supporting the special relay
• : All the QnACPU and QCPU
• QCPU: All the Q series CPU modules
• Q00J/Q00/Q01: Basic model QCPU
• Qn(H): High Performance model QCPU
• QnPH: Process CPU
• QnPRH: Redundant CPU
• QnU: Universal model QCPU
• QnA: QnA and Q2AS series CPU modules
• Rem: MELSECNET/H remote I/O module
• CPU module model: Only the specified model (Example: Q4ARCPU, Q3ACPU)