Main Content

Modbus RS485 Client Read

Client device reads data from server device register(s) over RS485 network

Since R2021b

expand all in page
  • MODBUS RS485 Client Read

Libraries:
Embedded Coder Support Package for STMicroelectronics STM32 Processors / STM32F746G-Discovery
Embedded Coder Support Package for STMicroelectronics STM32 Processors / STM32F769I-Discovery
Embedded Coder Support Package for STMicroelectronics STM32 Processors / STM32L475VG-Discovery (B-L475E-IOT01A)
Simulink Coder Support Package for STMicroelectronics Nucleo Boards / Common

Description

In the Modbus RS485 Client Read block, the client device reads data from the register(s) of the server device.

Simulink® Coder™ Support Package for STMicroelectronics® Nucleo Boards and Embedded Coder® Support Package for STMicroelectronics Discovery Boards supports the Modbus® communication protocol over the RS485 network. The client and the 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 server device registers referenced by the Modbus client device.

Register TypeRegister SizeAllowed Client Operation on Register
Coil1-bitRead and Write
Discrete Input1-bitRead
Holding Register16-bitRead and Write
Input Register16-bitRead

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

Examples

MODBUS RS485 Communication Between Client and Server Devices Using STMicroelectronics Discovery Board

MODBUS RS485 Communication Between Client and Server Devices Using STMicroelectronics Discovery Board

Use the Embedded Coder® Support Package for STMicroelectronics® STM32 Processors to implement a MODBUS® RS485 asynchronous, serial communication between MODBUS client and server devices. The example also shows the four modes of operation: Client Read, Client Write, Server Read, and Server Write.

Ports

Output

expand all

The block outputs the data read by the client from the server device register(s) as a N-by-1 vector, where N represents the number of registers on the server device.

  • If you select the Coil or Discrete Input read operations, the client reads the server 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 client reads the server registers as a 16-bit read operation. The block outputs the read data as uint16 data.

Data Types: Boolean | uint16

The block outputs the status of the client read operation on the server device register.

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

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

Data Types: uint8

Parameters

expand all

Enter the unique 8-bit Modbus server address or identifier to identify the server from which the client reads the data.

Select the type of read operation you want to perform on the server 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.

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

  • To notify the client to read data from a group of coil registers, specify the address of the first coil register in the group. For example, for the client 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.

Enter the number of coil registers from which you want the client to read the data. For example, for the client 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.

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

  • To notify the client 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 client 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.

Enter the number of discrete input registers from which you want the client to read the data. For example, for the client 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.

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

  • To notify the client to read data from a group of holding registers, specify the address of the first holding register in the group. For example, for the client 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.

Enter the number of holding registers from which you want the client to read the data. For example, for the client 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.

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

  • To notify the client to read data from a group of input registers, specify the address of the first input register in the group. For example, for the client 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.

Enter the number of input registers from which you want the client to read the data. For example, for the client 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.

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

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2021b

See Also

| |