Omron SYSMAC CJ1W-SCU21-V1, Operation Manual

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Setup Area Allocations (Modbus-RTU Slave Mode) Section 9-2
The Modbus-RTU command that access a specific Modbus data model is
used to read and write I/O memory areas in the CS/CJ-series CPU Unit.
Refer to
9-2 Setup Area Allocations (Modbus-RTU Slave Mode)
for the DM
Area settings to allocate areas. Refer to
9-3-4 Command and Response
Details
for details on Modbus-RTU commands.
Note 1. DM Area settings are read when the power is turned ON to the CPU Unit,
when the Serial Communications Board/Unit is restarted, or when the port
is restarted. Always cycle the power to the CPU Unit or restart the Serial
Communications Board/Unit or port after changing the settings.
2. Addresses in Modbus data models start from 1, but addresses specified in
Modbus-RTU commands and addresses in the CS/CJ-series CPU Unit
start from 0. To access address 0 in an area allocated in the CS/CJ-series
CPU Unit, specify address 100 in the Modbus-RTU command.
9-2 Setup Area Allocations (Modbus-RTU Slave Mode)
This section describes the Setup Area allocated to the Serial Communications
Board and Serial Communications Units in the DM Area when Modbus-RTU
slave communications are used.
9-2-1 Setup Area Words
The Serial Communications Board and Serial Communications Units use the
following words as a Setup Area in the DM Area when Modbus-RTU slave
communications are used. The words allocated to the Serial Communications
Board are different from those allocated to the Serial Communications Units
(which are allocated words according to the unit numbers).
Modbus Data Models
Discrete Inputs
Coils
Input Registers
Holding Registers
1
2
3
:
1
2
3
:
1
2
3
:
1
2
3
:
CIO Area
Work Area
Holding Area
DM Area
0
1
2
:
0
1
2
:
0
1
2
:
0
1
2
:
EM Area
0
1
2
:
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
DM Area settings are used to
allocate the area for each data
model except for discrete inputs.
I/O Memory
CS/CJ-series CPU Unit