Modbus RS485 Master Read

Master device reads data from slave device register(s) over RS485 network

Since R2020b

• 

Libraries:
Simulink Support Package for Arduino Hardware / Common

Description

In the Modbus RS485 Master Read block, the master device reads data from 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

Output

data — Output data

vector

The block outputs the data read by the master from the slave device register(s) 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 read operations, the master reads the slave registers as a 1-bit read operation. The block outputs the read data as Boolean data.

• If you select the Holding Register or Input Register read operations, the master reads the slave registers as a 16-bit read operation. The block outputs the read data as uint16 data.

Data Types: Boolean | uint16

status — Status of read operation

0 | 1

The block outputs the status of the master read operation on the slave device register.

• 0: Indicates an unsuccessful read operation, which means that the data received on the data port is invalid.

• 1: Indicates a successful read operation, which means that the data received on the data port is valid.

Data Types: uint8

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 from which the master reads the data.

Function — Type of read operation

Read Coil (default) | Read Discrete input | Read Holding register | Read Input register | Read Multiple Coils | Read Multiple Discrete inputs | Read Multiple Holding registers | Read Multiple Input registers

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

• Read Coil: Read data from the coil register address specified in the Coil Address parameter.

• Read Discrete input: Read data from the discrete input register address specified in the Discrete Input Address parameter.

• Read Holding register: Read data from the holding register address specified in the Holding Register Address parameter.

• Read Input register: Read data from the input register address specified in the Input Register Address parameter.

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

• Read Multiple Discrete inputs: Read data from multiple discrete input registers depending on the values specified in the Discrete Input Address and Number of Discrete Inputs parameters.

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

• Read Multiple Input registers: Read data from multiple input registers depending on the values specified in the Input Register Address and Number of Input registers parameters.

Coil Address — Address of coil register

0 (default) | scalar

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

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

Dependencies

To enable this parameter, set Function to Read Coil.

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

1 (default) | scalar

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

Dependencies

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

Discrete Input Address — Address of discrete input register

0 (default) | scalar

• To notify the master to read data from a specific discrete input register, specify the discrete input register address in this parameter. For example, for the master to read data from the discrete input register with the address 80, enter 80.

• To notify the master to read data from a group of discrete input registers, specify the address of the first discrete input register in the group. For example, for the master to read data from the discrete input registers with addresses ranging from 80 to 89, enter 80.

Dependencies

To enable this parameter, set Function to Read Discrete input.

Number of Discrete Inputs — Number of discrete input registers to be read by master

1 (default) | scalar

Enter the number of discrete input registers from which you want the master to read the data. For example, for the master to read data from the discrete input registers with addresses ranging from 80 to 89, enter 10.

Dependencies

To enable this parameter, set Function to Read Multiple Discrete inputs.

Holding Register Address — Address of holding register

0 (default) | scalar

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

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

Dependencies

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

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

1 (default) | scalar

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

Dependencies

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

Input Register Address — Address of input register

0 (default) | scalar

• To notify the master to read data from a specific input register, specify the input register address in this parameter. For example, for the master to read data from the input register with the address 25, enter 25.

• To notify the master to read data from a group of input registers, specify the address of the first input register in the group. For example, for the master to read data from the input registers with addresses ranging from 25 to 26, enter 25.

Dependencies

To enable this parameter, set Function to Read Input register.

Number of Input registers — Number of input registers to be read by master

1 (default) | scalar

Enter the number of input registers from which you want the master to read the data. For example, for the master to read data from the input registers with addresses ranging from 25 to 26, enter 2.

Dependencies

To enable this parameter, set Function to Read Multiple Input registers.

Sample Time — Time interval at which master reads data

0.1 (default) | scalar

Enter the time interval (in seconds) at which the master reads data from the slave device register(s).

Version History

Introduced in R2020b