
APPENDICES
APP - 6
MELSEC-A
Appendix 2 Special Relay, Special Register List
Appendix 2.1 Special Relay List
(1)
Special relay list
Special relays are internal relays whose uses are determined inside the PLC.
Therefore, they cannot be turned ON/OFF as coils is a program.
(Except for *1 and *2 in the table)
Table 2.1
Special relay list
Number
Name
Description
Details
Applicable CPU
1
M9000
Fuse blown
OFF: Normal
ON: Fuse blown unit
• Turned on when there is one or more output units of
which fuse has been blown or external power supply
has been turned off (only for small type). Remains on
if normal status is restored.
Output modules of remote I/O stations are also
checked fore fuse condition.
Usable with all
types of CPUs
Only remote I/O
station
information is
valid for A2C.
2
M9002
I/O unit
verify error
OFF: Normal
ON: Error
• Turned on if the status of I/O module is different from
entered status when power is turned on. Remains on
if normal status is restored.
I/O module verification is done also to remote I/O
station modules.
(Reset is enabled only when special registers D9116
to D9123 are reset.)
Usable with all
types of CPUs
Only remote I/O
station
information is
valid for A2C.
M9004
MINI link master
module error
OFF: Normal
ON: Error
• Turned on when the MINI (S3) link error is detected
on even one of the MINI (S3) link modules being
loaded. Remains on if normal status is restored.
—
Dedicated to AnA,
A2AS, AnU and
QCPU-A (A Mode).
1
M9005
AC DOWN
detection
OFF: AC power good
ON: AC power DOWN
• Turned on when an momentary power failure of 20
msec or less occurred.
Reset when POWER switch is moved from OFF to
ON position.
Usable with all
types of CPUs.
M9006
Battery low
OFF: Normal
ON: Battery low
• Turned on when battery voltage reduces to less than
specified. Turned off when battery voltage becomes
normal.
Usable with all
types of CPUs.
1
M9007
Battery low latch
OFF: Normal
ON: Battery low
• Turned on when battery voltage reduces to less than
specified. Remains on if battery voltage becomes
normal
Usable with all
types of CPUs.
1
M9008
Self-diagnostic
error
OFF: No error
ON: Error
• Turned on when error is found as a result of self-
diagnosis.
Usable with all
types of CPUs.
M9009
Annunciator
detection
OFF: No detection
ON: Detected
• Turned on when OUT F of SET F instruction is
executed. Switched off when D9124 data is zeroed.
Usable with all
types of CPUs.
M9010
Operation
error flag
OFF: No error
ON: Error
• Turned on when operation error occurs during
execution of application instruction. Turned off when
error is eliminated.
Unusable with
A3H, A3M, AnA,
A2AS, A3A board,
AnU and QCPU-A
(A Mode).
1
M9011
Operation
error flag
OFF: No error
ON: Error
• Turned on when operation error occurs during
execution of application instruction. Remains on if
normal status is restored.
Usable with all
types of CPUs.
M9012
Carry flag
OFF: Carry off
ON: Carry on
• Carry flag used in application instruction.
Usable with all
types of CPUs.
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