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MELSEC-Q
11 TROUBLESHOOTING
11.7 Special Register List
The special registers, SD, are internal registers with fixed applications in the PLC.
For this reason, it is not possible to use these registers in sequence programs in the same way
that normal registers are used.
However, data can be written as needed in order to control the CPU modules and remote I/O
modules.
Data stored in the special registers are stored as BIN values if no special designation has been
made to the contrary.
The headings in the table that follows have the following meanings.
Item Function of Item
Number • Indicates special register number
Name • Indicates name of special register
Meaning • Indicates contents of special register
Explanation • Discusses contents of special register 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.)
Corresponding ACPU
D9
• Indicates corresponding special register in ACPU (D9
)(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) SD1200 to SD1255 are used for QnACPU.
These relays are vacant with QCPU.
(2) Special register SD1500 and later are dedicated for Q4ARCPU.