Configuration as a Modbus Master MVI56E-MCM ♦ ControlLogix Platform
User Manual Modbus Communication Module
Page 44 of 209 ProSoft Technology, Inc.
2.3 Master Command Examples
2.3.1 Read Holding Registers 4x (Modbus Function Code 3)
The 4x holding registers are used for Analog Values such as Pressure,
Temperature, Current, and so on. These are 16-bit register values, but they can
also store Floating-Point Data Handling (Modbus Master) (page 49). You can
also write to these Modbus addresses using Modbus Function Codes 6 or 16.
Below is a sample command to read Modbus addresses 40001 to 40010 of node
1 on the Modbus network.
The module will send the command every time it goes through the
command list.
Places the data read from the Slave device into the module at address
1000. IntAddress 1000 of the module memory will be copied into the tag
MCM.DATA.READDATA[0].
Reads 10 consecutive registers from the Slave device.
Issues the Modbus command to node 1 on the network.
Issues Modbus Function Code 3 to Read Holding Registers.
Function Code 3, DevAddress of 0 will read address 40001
Along with a count of 10, this command reads 40001 to 40010.
2.3.2 Read Input Registers 3x (Modbus Function Code 4)
Like the 4x holding registers, 3x input registers are used for reading analog
values that are 16-bit register values. You can also use these registers to store
Floating-Point Data Handling (Modbus Master) (page 49). Unlike the 4x registers,
3x registers are Read Only.
Below is a sample command to read Modbus addresses 30021 to 30030 of node
1 on the Modbus network.
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