XIAO ESP32C3 as a Modbus TCP Client: Read Holding Registers

Modbus is a widely used communication protocol in industrial automation for interfacing various electronic devices. In this tutorial, we will explore how to create a Modbus client using the XIAO ESP32C3 microcontroller to read holding registers of Modbus TCP/IP devices. The XIAO ESP32C3, equipped with Wi-Fi connectivity, allows us to establish communication with Modbus TCP/IP devices over a network.

Prerequisites

XIAO ESP32C3 microcontroller board
A Modbus TCP/IP device (e.g., PLC, sensor, or any other Modbus-enabled device or Simulator)
Arduino IDE installed on your computer
Basic understanding of Modbus protocol

Install Modbus Library

To communicate with Modbus devices, we need to install the Modbus library. Follow these steps to install the library:

Open the Arduino IDE and navigate to Sketch > Include Library > Manage Libraries.
Search for "modbus-esp8266" and install the "modbus-esp8266" library.

Writing the Code

Now, let's write the code to create a Modbus client using the XIAO ESP32C3. Below is a sample code snippet to read holding registers from a Modbus TCP/IP device:

#include <WiFi.h>
#include <ModbusIP_ESP8266.h>

const char* ssid = "YourWiFiSSID";
const char* password = "YourWiFiPassword";

IPAddress remote(192, 168, 1, 7);  // Address of Modbus Slave device
const int START_REG = 0;           // Starting holding register
const int NUM_REGS = 10;           // Number of holding registers to read
const int INTERVAL = 5000;         // Interval between reads (in milliseconds)

WiFiClient client;
ModbusIP mb;

uint16_t res[NUM_REGS];
uint8_t show = NUM_REGS;  // Counter for displaying values
uint32_t LastModbusRequest = 0;  // Variable to track the last Modbus request time

void setup() {
  Serial.begin(115200);

  // Connect to WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());

  // Initialize Modbus client
  mb.client();
}

void loop() {
  if (millis() - LastModbusRequest >= INTERVAL) {
    LastModbusRequest = millis();

    if (mb.isConnected(remote)) {  
      // Read holding registers from Modbus Slave
      uint8_t transaction = mb.readHreg(remote, START_REG, res, 10, nullptr, 1);
      
      // Wait for the transaction to complete
      while(mb.isTransaction(transaction)) {
        mb.task();
        delay(10);
      }

      // Print holding register values
      Serial.println("Holding Register Values:");
      for (int i = 0; i < NUM_REGS; i++) {
        Serial.print("Register ");
        Serial.print(i);
        Serial.print(": ");
        Serial.println(res[i]);
      }
    } else {
      // If not connected, try to connect
      mb.connect(remote);
    }
  }
}

Replace "``YourWiFiSSID``" and "``YourWiFiPassword``" with your Wi-Fi credentials. Also, set the serverIP variable to the IP address of your Modbus TCP/IP device.

Upload the Code

Connect your XIAO ESP32C3 board to your computer using a USB cable. Select the correct board and port from the Tools menu, then click the "Upload" button to upload the code to your XIAO ESP32C3 board.

Testing

Once the code is uploaded successfully, open the Serial Monitor in Arduino IDE. You should see the XIAO ESP32C3 connecting to your Wi-Fi network and then attempting to read holding registers from the Modbus TCP/IP device. If everything is set up correctly, you should see the data received from the Modbus device in the Serial Monitor.

Conclusion

In this tutorial, we've learned how to create a Modbus client using the XIAO ESP32C3 microcontroller to read holding registers from Modbus TCP/IP devices. With this knowledge, you can now build your own Modbus-enabled IoT applications and integrate them into industrial automation systems. Experiment with different Modbus functions and parameters to explore more functionalities offered by the Modbus protocol.

Code

Sketch-1.ino

#include <WiFi.h>
#include <ModbusIP_ESP8266.h>

const char* ssid = "Capgemini_4G";
const char* password = "MN704116";

IPAddress remote(192, 168, 1, 7);  // Address of Modbus Slave device
const int START_REG = 0;           // Starting holding register
const int NUM_REGS = 10;           // Number of holding registers to read
const int INTERVAL = 1000;         // Interval between reads (in milliseconds)

WiFiClient client;
ModbusIP mb;

uint16_t res[NUM_REGS];
uint8_t show = NUM_REGS;  // Counter for displaying values
uint32_t LastModbusRequest = 0;  // Variable to track the last Modbus request time

void setup() {
  Serial.begin(115200);

  // Connect to WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());

  // Initialize Modbus client
  mb.client();
}

void loop() {
  if (millis() - LastModbusRequest >= INTERVAL) {
    LastModbusRequest = millis();

    if (mb.isConnected(remote)) {  
      // Read holding registers from Modbus Slave
      uint8_t transaction = mb.readHreg(remote, START_REG, res, 10, nullptr, 1);
      
      // Wait for the transaction to complete
      while(mb.isTransaction(transaction)) {
        mb.task();
        delay(10);
      }

      // Print holding register values
      Serial.println("Holding Register Values:");
      for (int i = 0; i < NUM_REGS; i++) {
        Serial.print("Register ");
        Serial.print(i);
        Serial.print(": ");
        Serial.println(res[i]);
      }
    } else {
      // If not connected, try to connect
      mb.connect(remote);
    }
  }
}