Communicating With Nj-Series Cpu Units Using Modbus - Omron CJ1W-SCU32 Operation Manual

7-1-3

Communicating with NJ-series CPU Units Using Modbus

There are four data models that are defined for Modbus.
Settings in the device variable for CJ-series Unit for System Settings are used to allocate each area of
these data models in the memory used for CJ-series Unit of the NJ-series CPU Unit for use by the
Serial Communications Unit.
Modbus data model areas
1 Discrete Inputs:
2 Coils:
3 Input Registers:
4 Holding Registers:
The Modbus-RTU command that accesses a specific Modbus data model is used to read and write
memory areas used for CJ-series Unit in the NJ-series CPU Unit. It is also necessary to allocate user-
defined variables when accessing the memory used for CJ-series Unit from the user program. For
details on creating user-defined variables, refer to 2-2-2 How to Specify and Create Variables.
NJ-series CPU Unit
User program
User-defined
variable
Refer to 7-2 Device Variables for CJ-series Unit and System-defined Variables (Modbus-RTU Slave
Mode) for the setting allocation areas using system settings.
Refer to 7-3 Command and Response Details for details on Modbus-RTU commands.
Precautions for Safe Use
System Settings become valid when the Controller is reset, when the Serial Communications
Unit is restarted, or when the port is restarted. If any of the allocations are changed, reset the
Controller or restart the Serial Communications Unit or port after the safety of the connection
destination is confirmed.
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
Allocated CJ Unit memory of NJ-series CPU Unit
CIO Area (fixed)
CIO, Work, Holding, or Auxiliary Area
CIO, Work, Holding, or Auxiliary Area
DM or EM Area
Memory used for CJ-series Unit
0
CIO
1
2
:
0
WR
1
2
:
0
HR
1
2
:
0
DM
1
2
:
0
EM
1
Use the settings of device variables for
2
CJ-series Unit for System Settings to
:
allocate the area for each data model
except for discrete inputs.
7 Using Modbus-RTU Slave Mode
Serial Communications Unit
Modbus Data Models
1
Discrete Inputs
2
3
:
1
Coils
2
3
:
1
Input Registers
2
3
:
1
Holding Registers
2
3
:
Modbus-RTU command
Modbus Commands
Read Coils
Read Discrete Inputs
Read Holding Registers
Read Input Registers
Write Single Coil
Write Single Register
Write Multiple Coils
Write Multiple Registers
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