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Appendix 4 Special Register (SD) for MELSECNET/H
(MELSECNET/10 Mode) Remote I/O Station
The special register (SD) is an internal register whose application is fixed in the programmable controller. For this
reason, the special register cannot be used in the same way as other internal registers used in sequence programs.
However, data can be written to the special register to control the CPU module or the MELSECNET/H remote I/O
module as needed. Data is stored in binary format if not specified. To monitor and write data to the special register 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 register areas related to the MELSECNET/H remote I/O module. The
following table shows how to read the special register 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 register number
Name Special register name
Meaning Description of special register
Explanation Detailed description of special register
Set by
(When Set)
Set side and set timing of special register
<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
D9
• Special register (D9) supported by the ACPU ("D9 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 register
• : 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)