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App. - 4
Appendix 2 Special Relay
The special relay (SM) is an internal relay 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 are used in sequence programs. However, the
bit of the special relay can be turned on or off as needed to control the CPU module.
The following shows how to read the items in the list.
For details of special relays, refer to QCPU User's Manual Hardware Design,
Maintenance and Inspection.
Item Description
Number • Indicates the special relay number.
Name • Indicates the special relay name.
Meaning • Indicates the contents of the special relay.
Explanation • Explains the contents of the special relay in detail.
Set by
(When set)
• Indicates the setting side and setting timing of the special register.
<Set by>
S : Set by the system
U : Set by user (in sequence program or test operation at a peripheral
device)
S/U : Set by both system and user
<When set>
indicated only if setting is done 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
□□□
• Indicates a special relay (M9
□□□) supported by the ACPU.
("M9
□□□ format change" indicates the one whose application has been
changed. Incompatible with the Q00J/Q00/Q01, and QnPRH.)
• "New" indicates the one added for the Q-series CPU.
Corresponding
CPU
Indicates the CPU module supporting the special relay.
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
CPU module name : Only the specified CPU model (Example: Q02U)
For details on the following items, refer to these manuals:
• For network related items
Manuals for each network module
• For SFC programs
MELSEC-Q/L/QnA Programming Manual (SFC)
POINT
Do not change the values of special relays set by the system using a program
or by test operation.
Doing so may result in a system down or communication failure.