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7 Using Modbus-RTU Slave Mode
7-2
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
7-1 Modbus-RTU Slave System
A Modbus-RTU Slave System can be used to send Modbus-RTU commands from a host computer
(e.g. personal computer) to read and write the memory used for CJ-series Unit of the CPU Unit of the
NJ-series Controller.
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Host-initiated Communications
Communications in a Modbus-RTU Slave System are started by the host computer.
The host computer sends a command to the controller. The controller processes the command and
returns a response to the host computer. This process is repeated, allowing the host computer to
monitor and control controller operation.
Additional Information
Only the Modbus-RTU Slave Mode is supported. The Modbus-ASCII Slave Mode is not sup-
ported by the Serial Communications Units.
*1 Modbus-ASCII Mode is not supported.
*2 The data length is fixed at 8 bits and cannot be changed by the user.
*3 The number of stop bits is automatically determined by the parity and cannot be set by the user.
*4 The address cannot be set to 0. In commands, 0 is used for broadcast commands.
7-1-1 Modbus-RTU Slave System
7-1-2 Modbus-RTU Specifications
Item Description
Mode Modbus-RTU Slave Mode (*1)
Baud rate 1,200/2,400/4,800/9,600/19,200/38,400/57,600/115,200/230,
400 bps
Default: 19,200 bps
Data length 8 bits (*2)
Parity Odd, even, or none
Default: Even
Stop bits Odd or even parity:1 bit
No parity: 2 bits (*3)
Address setting
range 1 to 247 (broadcasting: 0) (*4)
Frame format Slave address: 1 byte
Function code: 1 byte
Data: 0 to 252 bytes
CRC code: 2 bytes
Host computer NJ-series Controller
Command
Response