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Modbus RS485 Server Read

Server device reads data from the server device register over RS485 network

Since R2021b

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  • MODBUS RS485 Server 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 Server Read block, the server device reads data from its registers. The server can read data only from one register per read operation.

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. Each device on the RS485 network is referenced by a unique 8-bit address or identifier.

This table categories the server registers referenced by the Modbus server device.

Register TypeRegister Size
Coil1-bit
Discrete Input1-bit
Holding Register16-bit
Input Register16-bit

The server can perform either a read or a write operation on its registers.

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

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The block outputs the data read by the server device from its register as a 1-bit scalar.

  • If you select the Coil or Discrete Input read operations, the server reads its registers as a 1-bit read operation. The block outputs the read data as a Boolean data type.

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

Data Types: Boolean | uint16

The block outputs the status of the server read operation on the server 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

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

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

Dependencies

To enable this parameter, set Function to Read Coil.

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

Dependencies

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

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

Dependencies

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

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

Dependencies

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

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

Extended Capabilities

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

Version History

Introduced in R2021b

See Also

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