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Troubleshooting Section 11-3
Serial commu-
nications
mode
Indicator
status
Status
information,
etc.
CIO Area Cause Remedy
Serial commu-
nications mode
is set to Mod-
bus-RTU slave
mode.
The RD@/SD@
and COM@
indicators are
flashing, and an
error response
has returned to
the host.
The RD@/SD@
and COM@
indicators are
flashing, but
sometimes
there is no
response
returned.
There is no
transmission
error.
CIO Area words n +
8/n + 18 (transmis-
sion error status)
are set to 0000 Hex.
A command was
sent from the host
with incorrect
parameters.
Review the host’s settings
and program (such as
parameter settings) based
on the response contents.
There is a
transmission
error.
In CIO Area words n
+ 8/n + 18, bit 15
(transmission error
status) is turned
ON, and bit 07(CRC
error), bit 04 (over-
run error), bit 03
(framing error), or
bit 02 (parity error)
is turned ON.
The communica-
tions conditions and
baud rate do not
match the settings
at the host.
Review the System Setup,
the host’s settings and pro-
gram (such as commands
and frame format) based
on the response contents,
and the transmission error
codes in CIO Area words n
+ 8/n + 18.
There is a
transmission
error some-
times.
In CIO Area words n
+ 8/n + 18, bit 15
(transmission error
status) is turned
ON, and bit 07(CRC
error), bit 04 (over-
run error), bit 03
(framing error), or
bit 02 (parity error)
is turned ON.
The baud rate is
outside the allow-
able range, and the
stop bits do not
match, causing the
bits to be out of
alignment.
Review the System Setup.
Review the host’s settings
and program (such as
baud rate and frame for-
mat).
There is a
transmission
error some-
times.
Terminating resis-
tance switch (TERM
ON/OFF) status
Cables are incor-
rectly connected.
The RS-422A/485
port terminating
resistance setting is
incorrect.
Adapters such as
the NT-AL001-E are
incorrectly wired or
the terminating
resistance is incor-
rectly set.
Check the wiring.
Turn ON the terminating
resistance of the Board
and the last node by using
the terminating resistance
switch. Turn OFF the ter-
minating resistance of
other nodes.
There is a
transmission
error some-
times.
CIO Area words n +
8/n + 18 (transmis-
sion error status)
are not set to 0000
Hex.
Transmission errors
are occurring that
are caused by noise
interference.
Use shielded twisted-pair
cables.
Lay power lines sepa-
rately using ducts.
Review the installation
environment to reduce
noise interference.
Programming retry pro-
cessing for communica-
tions if necessary.
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