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    Modbus TCP is a protocol used for communication between devices over a TCP/IP network. It is widely used in industrial automation systems. In this guide, we will demonstrate how to set up an Arduino as a Modbus TCP slave using the Ethernet shield.

    Setting Up the Arduino

    To set up the Arduino as a Modbus TCP slave, you will need the following libraries:

    • SPI.h

    • Ethernet.h

    • ArduinoRS485.h

    • ArduinoModbus.h

    Here is a sample code to get you started:

    #include <SPI.h>
    #include <Ethernet.h>
    #include <ArduinoRS485.h> // ArduinoModbus depends on the ArduinoRS485 library
    #include <ArduinoModbus.h>

    // Enter a MAC address and IP address for your controller below
    // The IP address will be dependent on your local network
    // gateway and subnet are optional:
    byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
    IPAddress ip(192, 168, 1, 177);
    IPAddress myDns(192, 168, 1, 1);
    IPAddress gateway(192, 168, 1, 1);
    IPAddress subnet(255, 255, 0, 0);

    EthernetServer server(502);
    ModbusTCPServer modbusTCPServer;

    void setup() {
    // initialize the ethernet device
    Ethernet.begin(mac, ip, myDns, gateway, subnet);

    // Open serial communications and wait for port to open:
    Serial.begin(9600);
    while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
    }

    // Check for Ethernet hardware present
    if (Ethernet.hardwareStatus() == EthernetNoHardware) {
    Serial.println("Ethernet shield was not found. Sorry, can't run without hardware. :(");
    while (true) {
    delay(1); // do nothing, no point running without Ethernet hardware
    }
    }
    if (Ethernet.linkStatus() == LinkOFF) {
    Serial.println("Ethernet cable is not connected.");
    }

    // start listening for clients
    server.begin();

    Serial.print("Modbus server address:");
    Serial.println(Ethernet.localIP());

    // start the Modbus TCP server
    if (!modbusTCPServer.begin()) {
    Serial.println("Failed to start Modbus TCP Server!");
    while (1);
    }

    // configure the LED
    pinMode(LED_BUILTIN, OUTPUT);
    digitalWrite(LED_BUILTIN, LOW);

    // configure a single coil at address 0x00
    modbusTCPServer.configureCoils(0x00, 1);
    }

    void loop() {
    // wait for a new client:
    EthernetClient client = server.available();

    // when the client sends the first byte, say hello:
    if (client) {
    // a new client connected
    Serial.println("new client");

    // let the Modbus TCP accept the connection
    modbusTCPServer.accept(client);

    while (client.connected()) {
    // poll for Modbus TCP requests, while client connected
    modbusTCPServer.poll();

    // update the LED
    updateLED();
    }

    Serial.println("client disconnected");
    }
    }

    void updateLED() {
    // read the current value of the coil
    int coilValue = modbusTCPServer.coilRead(0x00);

    if (coilValue) {
    // coil value set, turn LED on
    digitalWrite(LED_BUILTIN, HIGH);
    } else {
    // coil value clear, turn LED off
    digitalWrite(LED_BUILTIN, LOW);
    }
    }
    Copied!
    How do I connect two Arduino boards using Modbus TCP?
    To set up communication between the two Arduino boards using the Modbus TCP and the Arduino Modbus library, install Ethernet shields on the two boards and connect both Arduinos to the same network through the Ethernet cables or a WiFi connection. Upload the following sketch to Arduino configured as a Modbus transmitter.
    engineersgarage.com
    Arduino Forum
    https://forum.arduino.cc/t/arduino-modbus-tcp-slave-server-ide-exampl…
    Arduino Modbus TCP Slave (server): IDE example
  1. deepwiki.com
    https://deepwiki.com › arduino-libraries › ArduinoModbus

    TCP Examples | arduino-libraries/ArduinoModbus | DeepWiki

    Apr 30, 2025 · This document explains the Modbus TCP examples provided with the ArduinoModbus library. These examples demonstrate how to implement Modbus TCP client and server functionality …

  2. Arduino Forum
    https://forum.arduino.cc › arduino-modbus-tcp...

    Arduino Modbus TCP Slave (server): IDE example

    May 9, 2019 · That's a simple combination of a Ethernet server sketch with the WiFiModbusServerLED sketch example of the linked library (not tested):

  3. Arduino Getting Started
    https://arduinogetstarted.com › tutorials › arduino-modbus

    Arduino - Modbus | Arduino Tutorial

    As described earlier, An Arduino can communicate with software/app, HMI device, or another Arduino via Modbus protocol. This tutorial takes communication between two Arduino as an example of Modbus communication.

  5. GitHub Gist
    https://gist.github.com › bungernut

    Arduino Ethernet Modbus Server Example · GitHub

    Mar 6, 2025 · Arduino Ethernet Modbus Server Example. GitHub Gist: instantly share code, notes, and snippets.

  6. Industrial Shields
    https://www.industrialshields.com › blog › arduino...

    Modbus TCP example for INDUSTRIAL uses

    Mar 25, 2020 · 👇 ESP32 and Arduino Modbus TCP example with Ethernet shield assembled to a PLC Arduino for Industrial application. Check the Modbus TCP master client library.

  7. Engineers Garage
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    How to convert Arduino into a Modbus device

    Sep 26, 2023 · In this article, we’ll turn Arduino into a Modbus device using Modbus ASCII/RTU and Modbus TCP. To do so, we’ll set-up communication between two Arduino boards on Modbus.

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    https://www.circuits-diy.com › modbus-arduino-tutorial

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  11. Github
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  12. Elektor Magazine
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