Converting To Modbus-Rtu - Omron CJ1W-SCU32 Operation Manual

5 Serial Gateway
1:N RS-485 Connection Example Using RS-422A/485 Port
Serial Communications Unit
Signal
RDA
RS-422A/
RDB
485 Inter-
SDA
face
SDB
FG
Terminal block connector
Note Be sure to connect a terminating resistance of between 100 and 125Ω(1/2W) to the terminals
of the remote devices at either end of the RS-422A/485 transmission path. (Set the terminat-
ing resistance on this Unit by using Terminating resistance ON/OFF switch located on the
front panel of the Unit.
5-4-4

Converting to Modbus-RTU

It is possible to access Modbus-RTU Slave-compatible devices (including OMRON inverters) that are
connected to a PLC via a serial network (Modbus-RTU) from a PLC or PT by sending Modbus-RTU
commands.
• Sent message: header + command code 2804 hex + Modbus-RTU command
• Message after conversion: Modbus-RTU command
CPU Unit (Send-
Cmd instruction)
Header
or PT (Program-
mable Terminal)
Modbus-RTU command encapsulated using
command 2804 hex
Examples of Modbus-RTU Slave OMRON Devices
Type
Inverters
Temperature Controllers
5-26
Device that supports
RS-422A/485
communications
(2-wire)
Signal
Pin
RS-422A/
485 Inter-
1 A(−)
face
B(+)
2
3
4
5
Device that supports
RS-422A/485
communications
(2-wire)
Signal
RS-422A/
485 Inter-
A(−)
face
B(+)
Modbus-RTU command
2804
(Via network or CPU bus)
Model series
3G3MX2
3G3RX
3G3JX
E5CN
EJ1
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
Modbus-RTU command
Serial Communi-
Modbus-RTU command
cations Unit
(RS-232C or RS-422A/485)
Modbus-RTU
Slave-
compatible
device
(OMRON
Inverter, etc.)