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MELSEC-Q
11 TROUBLESHOOTING
11.6 Special Relay List
Special relays, SM, are internal relays whose applications are fixed in the PLC.
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 and
remote I/O modules.
The headings in the table that follows have the following meanings.
Item Function of Item
Number • Indicates the number of the special relay.
Name • Indicates the name of the special relay.
Meaning • Indicates the nature of the special relay.
Explanation • Contains detailed information about the nature of the special relay.
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 (in sequence program or test operation at a GX Developer)
S/U : Set by both system and user
<When set>
Indicated only if setting is done 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 is generated
Instruction execution : Set when instruction is executed
Request : Set only when there is a user request
(through SM, etc.)
Corresponding ACPU
M9
• Indicates special relay M9 corresponding to the ACPU.
(Change and notation when there has been a change in contents)
• Items indicated as "New" have been newly added for High performance model
QCPU/QnACPU.
Corresponding CPU
• Indicates the corresponding CPU module type name.
+Rem: Can be applied to all CPU module types and MELSECNET/H remote I/O modules.
: Can be applied to all types of CPU module
QCPU: Can be applied to High Performance model QCPU
QnA: Can be applied to QnA series and Q2ASCPU Series
Remote: Can be applied to the MELSECNET/H remote I/O modules.
Each CPU type name: Can be applied only to the specific CPU module. (e.g. Q4ARCPU,
Q3ACPU)
For details on the following items, refer to the following manuals:
• Networks
• For Q Corresponding MELSECNET/H Network System Reference Manual
(PLC to PLC network)
• For Q Corresponding MELSECNET/H Network System Reference Manual
(Remote I/O network)
• For QnA/Q4AR MELSECNET/10 Network System Reference Manual
• SFC
QCPU(Q Mode)/QnACPU Programming Manual (SFC)
POINT
(1) SM1200 to SM1255 are used for QnACPU.
These relays are vacant with QCPU.
(2) Special relays SM1500 and later are dedicated for Q4ARCPU.