Implement Modbus RTU and TCP with STM32 HAL for Industrial Sensors

Implementing Modbus RTU over UART and Modbus TCP using STM32 HAL Library for Industrial Sensor Communication

Modbus is a widely adopted communication protocol in industrial applications, allowing devices to communicate over serial lines (Modbus RTU) or TCP/IP networks (Modbus TCP). This tutorial will guide you through implementing Modbus RTU over UART and Modbus TCP using the STM32 HAL library to facilitate communication with industrial sensors.

Prerequisites

• Basic knowledge of embedded systems and C programming.
• STM32 development board (e.g., STM32F4 series).
• STM32CubeIDE installed on your computer.
• Modbus protocol understanding.
• Industrial sensor compatible with Modbus RTU or TCP.

Parts/Tools

• STM32 development board.
• USB to UART converter (for Modbus RTU).
• Ethernet cable (for Modbus TCP).
• Industrial sensors (e.g., temperature, pressure sensors).
• STM32CubeMX for configuration.

Steps

1. Setting Up the STM32 Project:
   1. Open STM32CubeIDE and create a new STM32 project.
   2. Select your STM32 microcontroller and initialize the project.
   3. Use STM32CubeMX to configure the following peripherals:
      • UART for Modbus RTU.
      • Ethernet for Modbus TCP.
   4. Generate the project code.
2. Implementing Modbus RTU over UART:
   1. Include necessary headers in your main code file:

   #include "modbus.h"
   #include "usart.h"

   2. Configure UART settings in usart.c:

   UART_HandleTypeDef huart1;
   // UART1 configuration
   huart1.Instance = USART1;
   huart1.Init.BaudRate = 9600;
   huart1.Init.WordLength = UART_WORDLENGTH_8B;
   huart1.Init.StopBits = UART_STOPBITS_1;
   huart1.Init.Parity = UART_PARITY_NONE;
   HAL_UART_Init(&huart1);

   3. Initialize Modbus RTU parameters:

   modbus_t modbus;
   modbus_init(&modbus, &huart1);

   4. Implement the main communication loop:

   while (1) {
       modbus_task(&modbus);
   }

3. Implementing Modbus TCP:
   1. Include required headers for Ethernet:

   #include "lwip.h"
   #include "modbus.h"

   2. Initialize the Ethernet stack:

   lwip_init();

   3. Set up Modbus TCP parameters:

   modbus_t modbus_tcp;
   modbus_tcp_init(&modbus_tcp);

   4. Implement the Modbus TCP server loop:

   while (1) {
       modbus_tcp_task(&modbus_tcp);
   }

4. Testing Communication with Sensors:
   1. Connect your sensors to the appropriate UART or Ethernet ports.
   2. Use a Modbus client tool (e.g., Modbus Poll) to test communication:

   Function Code: Read Holding Registers
   Address: 0x01
   Register: 0x0000

   3. Verify that you receive the expected responses from your sensors.

Troubleshooting

• Communication Issues:
  • Check wiring and connections.
  • Verify Baud rate settings on both the STM32 and the sensor.
  • Ensure Modbus addresses are correctly set.
• Errors in Responses:
  • Check for correct function codes and register addresses.
  • Ensure the sensor supports the requested Modbus commands.
• TCP Connection Problems:
  • Check Ethernet cable and connection.
  • Verify IP configurations.
  • Ensure no firewall is blocking the Modbus TCP port (default 502).

Conclusion

In this tutorial, you have learned how to implement Modbus RTU over UART and Modbus TCP using the STM32 HAL library. By following the outlined steps, you should be able to establish communication with industrial sensors effectively. Ensure to troubleshoot any issues that may arise during implementation for a smooth experience.