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9-23
9 Troubleshooting and Maintenance
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
9-3 T
rou
b
lesho
o
ting
9
9-3-4 Modb
us-R
TU
Sla
v
e Mode
Note The system settings can not be changed unless the power supply is cycled, the Unit is restarted,
or the port is restarted. Refer to 1-8 Basic Operating Procedure for details.
Error conditions Confirmation of
device variable
for CJ-series Unit,
etc.
Cause Remedy
Serial
communications
mode
Indicator
status
Status
information,
etc.
Serial communi-
cations mode is
set to Modbus-
RTU Slave Mode. The RD @ indica-
tors flash, but the
response was not
returned from the
host.
The SD @ indicator
does not flash at
all. (Communica-
tions were electri-
cally established.)
There is no
transmission
error. --- Cables are incorrectly
connected.
The RS-422A/485
port setting (2-wire or
4-wire) is incorrect.
Adapters such as the
NT-AL001 are incor-
rectly wired or set.
Check the wiring.
This is a transmission
circuit hardware error. Conduct a loopback test to
check the transmission lines.
If an error occurs during the
test, replace the Unit.
The destination Mod-
bus slave address in
the command frame is
set to 0, i.e., it is set
for a broadcast. Correct the destination Mod-
bus slave address in the com-
mand frame.
There is a
transmission
error. *_P1(orP2)_TransErr
(Transmission error) is
set to TRUE, or any of
*_P1(orP2)_OverRun
Err (Overrun Error),
*_P1(orP2)_FramingE
rr (Framing Error),
*_P1(orP2)_ParityErr
(Parity Error),
*_P1(orP2)_FCSErr
(FCS Check Error) is
set to TRUE. The communications
conditions and baud
rate do not match the
settings at the host. Review the System Settings,
the host's settings and pro-
gram (such as commands
and frame format) based on
the response contents, and
the transmission error codes
in *_P1(orP2)_TransErrSta
(Transmission Error Status).
There is noise interfer-
ence. Use shielded twisted-pair
cables.
Lay power lines separately by
using ducts.
Review the installation envi-
ronment to reduce noise inter-
ference.
There is an error in
the CRC code
appended to the host
command frame. Append the correct CRC
code.