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7-13
7 Using Modbus-RTU Slave Mode
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
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7-3 Command and Response Details
The Modbus-RTU Slave Mode of the Serial Communications Unit supports the following Modbus-RTU
commands.
The frame format used in Modbus-RTU Slave Mode is as follows:
* The CRC code is given in the order of low byte to high byte.
Additional Information
• Set the slave address to 0 for a broadcast command. Responses are not returned for broad-
cast commands.
• Modbus data models are allocated to the memory used for CJ-series Unit by the System Set-
tings. System settings are read when the Controller is reset, when the Serial Communications
Unit is restarted, or when the port is restarted.
Precautions for Correct Use Precautions for Correct Use
Create a program for retry processing on the host computer (e.g. personal computer) for a trans-
mission error or other communications errors.
7-3-1 Supported Modbus-RTU Commands
Function code
(hexadecimal)
Function Modbus name
01 Reads multiple bits from the CIO, Work,
Holding, or Auxiliary Area of the memory
used for CJ-series Unit Read Coils
02 Reads multiple bits from the CIO Area of
the memory used for CJ-series Unit Read Discrete Inputs
03 Reads multiple words from the DM or
EM Area of the memory used for CJ-
series Unit Read Holding Registers
04 Reads multiple words from the CIO,
Work, Holding, or Auxiliary Area of the
memory used for CJ-series Unit Read Input Registers
05 Writes a bit in the memory used for CJ-
series Unit Write Single Coil
06 Writes a word in the DM or EM Area of
the memory used for CJ-series Unit. Write Single Register
08 Executes an echoback test. Diagnostic
0F Writes multiple bits in the memory used
for CJ-series Unit Write Multiple Coils
10 Writes multiple words in the DM or EM
Area of the memory used for CJ-series
Unit Write Multiple Registers
Slave address Function code Data CRC
1 byte 1 byte 0 to 252 bytes 2 bytes (*)