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9 Troubleshooting and Maintenance
9-22
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
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.
9-3-4 Modbus-RTU Slave Mode
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
not set to Modbus-
RTU Slave Mode. --- --- Bits 12 to 15 (Serial
communications
mode) of
*_P1(orP2)_SysSetSta
are set to a value other
than A hex. Serial communica-
tions mode is not set
correctly. Set bits 08 to 11 (Serial com-
munications mode) of
*_P1(orP2)_PortCfg to A hex
(Modbus-RTU Slave Mode).
Serial communi-
cations mode is
set to Modbus-
RTU Slave Mode. The SD
@
/RD
@
indicators do not
flash at all. (Com-
munications were
not electrically
established.)
--- --- 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.
Check the setting of the 2/4-
wire switch.
Wire all nodes by using the 4-
wire method.
Commands are not
sent from the host. Reset the serial port at the
host, and rewrite the program.
A hardware error
occurred. Set bits 08 to 11 (Serial com-
munications mode) of
*_P1(orP2)_PortCfg to Loop-
back Tast Mode and conduct
a loopback test by setting
*_P1(orP2)_LbtTestTrigCmd
to TRUE. The test data is
reflected in
*_P1(orP2)_LbtSta.
If an error occurs during the
test, replace the Unit.
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. • *_P1(orP2)_TransErr
Sta (Transmission
Error Status) is set
to 0000 hex.
• The settings in
*_P1(orP2)_SysSet
Sta (System Set-
ting) do not match
the settings for
those of the remote
device.
*_P1(orP2)_MbsSlav
AdrCfg (Modbus-RTU
Slave Address) of the
Unit does not corre-
spond to the settings
for the remote device.
The command format
and data length of the
data sent from the
host are incorrect.
• Correct the setting in
*_P1(orP2)_MbsSlavAdrCf
g (Modbus-RTU Slave
Address).
• Correct the command frame
(destination Modbus slave
address) and the program.