Modbus RS485 Server Read

R2026b

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

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Modbus RS485 Server Read Block block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
STM32 Microcontroller Blockset / (Legacy) STM32 MBED Based Boards / Common
STM32 Microcontroller Blockset / (Legacy) STM32 MBED Based Boards / STM32F746G-Discovery
STM32 Microcontroller Blockset / (Legacy) STM32 MBED Based Boards / STM32F769I-Discovery
STM32 Microcontroller Blockset / (Legacy) STM32 MBED Based Boards / STM32L475VG-Discovery (B-L475E-IOT01A)

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 Type	Register Size
Coil	1-bit
Discrete Input	1-bit
Holding Register	16-bit
Input Register	16-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

Use the STM32™ Microcontroller Blockset 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.

• Open Model

Ports

Output

data — Output data

scalar

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

status — Status of read operation

0 | 1

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

Function — Type of read operation

Read Coil (default) | Read Discrete input | Read Holding register | Read Input register

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

Coil Address — Address of coil register

0 (default) | scalar

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.

Discrete Input Address — Address of discrete input register

0 (default) | scalar

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.

Holding Register Address — Address of holding register

0 (default) | scalar

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.

Input Register Address — Address of input register

0 (default) | scalar

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.

Sample Time — Time interval at which server reads data

0.1 (default) | scalar

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

Programmatic Use: Add Block

To add the block programmatically, use the add_block function with one of these library block paths as the source.

"stm32nucleodiscoboardslib/Common/Modbus RS485 Server Read"

"stm32f7lib/Modbus RS485 Server Read"

"stm32f769ilib/Modbus RS485 Server Read"

"stm32l475vglib/Modbus RS485 Server Read"

Example: add_block("stm32nucleodiscoboardslib/Common/Modbus RS485 Server Read","myModel/myBlock",MakeNameUnique="on")

Extended Capabilities

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

Version History

Introduced in R2021b