Modbus RS485 Master Write

Master device writes data to slave device register(s) over RS485 network

Since R2020b

• 

Libraries:
Simulink Support Package for Arduino Hardware / Common

Description

In the Modbus RS485 Master Write block, the master device writes data to the register(s) of the slave device.

Simulink^® Support Package for Arduino^® Hardware supports the Modbus^® communication protocol over the RS485 network. The master (client) and the slave (server) must be connected on the same RS485 network for successful Modbus communication. Each device on the RS485 network is referenced by a unique 8-bit address or identifier.

This table categories the slave device registers referenced by the Modbus master device.

Register Type	Register Size	Allowed Master Operation on Register
Coil	1-bit	Read and Write
Discrete Input	1-bit	Read
Holding Register	16-bit	Read and Write
Input Register	16-bit	Read

The master can perform either a read or a write operation (depending on the register type) on register(s) of a slave device.

Ports

Input

data — Input data

vector

The input to the block is the data to be written to the slave register(s) by the master as a N-by-1 vector, where N represents the number of registers on the slave device.

• If you select the Coil or Discrete Input write operations, the master writes data to the slave registers as a 1-bit write operation having the Boolean data type.

• If you select the Holding Register or Input Register write operations, the master writes data to the slave registers as a 16-bit write operation having the uint16 data type.

Data Types: Boolean | uint16

Parameters

Slave address — Unique 8-bit Modbus slave identifier

1 (default) | scalar in the range [1, 255]

Enter the unique 8-bit Modbus slave address or identifier to identify the slave to which the master writes the data.

Function — Type of write operation

Write Coil (default) | Write Holding register | Write Multiple Coils | Write Multiple Holding registers

Select the type of write operation you want to perform on the slave register(s). Specify any one of the following:

• Write Coil: Write data to the coil register address specified in the Coil Address parameter

• Write Holding register: Write data to the holding register address specified in the Holding Register Address parameter

• Write Multiple Coils: Write data to multiple coil registers depending on the values specified in the Coil Address and Number of Coils parameters

• Write Multiple Holding registers: Write data to multiple holding registers depending on the values specified in the Holding Register Address and Number of Holding registers parameters

Coil Address — Address of coil register

0 (default) | scalar

• To notify the master to write data to a specific coil register, specify the coil register address in this parameter. For example, for the master to write data to the coil register with the address 10, enter 10.

• To notify the master to write data to a group of coil registers, specify the address of the first coil register in the group. For example, for the master to write data to the coil registers with addresses ranging from 10 to 14, enter 10.

Dependencies

To enable this parameter, set Function to Write Coil.

Number of Coils — Number of coil registers to be written by master

1 (default) | scalar

Enter the number of coil registers to which you want the master to write the data. For example, for the master to write data to the coil registers with addresses ranging from 10 to 14, enter 5.

Dependencies

To enable this parameter, set Function to Write Multiple Coils.

Holding Register Address — Address of holding register

0 (default) | scalar

• To notify the master to write data to a specific holding register, specify the holding register address in this parameter. For example, for the master to write data to the holding register with the address 37, enter 37.

• To notify the master to write data to a group of holding registers, specify the address of the first holding register in the group. For example, for the master to write data to the holding registers with addresses ranging from 37 to 44, enter 37.

Dependencies

To enable this parameter, set Function to Write Holding register.

Number of Holding registers — Number of holding registers to be written by master

1 (default) | scalar

Enter the number of holding registers from which you want the master to write the data. For example, for the master to write data to the holding registers with addresses ranging from 37 to 44, enter 8.

Dependencies

To enable this parameter, set Function to Write Multiple Holding registers.

Version History

Introduced in R2020b