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Troubleshooting Section 11-3
Serial commu-
nications mode
is set to Mod-
bus-RTU slave
mode.
The RD@ and
COM@ indica-
tors are flash-
ing, but the
response has
not been
returned from
the host.
For the Unit, the
SD@ indicator
does not flash
at all (Commu-
nications have
been electri-
cally estab-
lished.)
There is no
transmission
error.
--- Cables are incor-
rectly connected.
The RS-422A/485
port setting (2-wire
or 4-wire) is incor-
rect.
Adapters such as
the NT-AL001-E are
incorrectly wired or
set.
Check the wiring.
Reset the port to the cor-
rect wiring setting.
Wire all nodes using the 4-
wire method.
--- This is a transmis-
sion circuit hard-
ware error.
Conduct a loopback test in
serial communications
mode to check the trans-
mission lines. If an error
occurs during the test,
replace the Board or Unit.
The destination
Modbus slave
address in the com-
mand frame is set to
0, i.e., it is set for a
broadcast.
Correct the destination
Modbus slave address in
the command frame.
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 noise inter-
ference.
Use shielded twisted-pair
cables.
Lay power lines sepa-
rately using ducts.
Review the installation
environment to reduce
noise interference.
There is an error in
the CRC code
appended to the
host command
frame.
Append the correct CRC
code.
Serial commu-
nications
mode
Indicator
status
Status
information,
etc.
CIO Area Cause Remedy
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