Introduction

Modbus TCP is a robust and widely used protocol for communication over Ethernet in industrial automation systems. It allows seamless integration between devices, providing reliable data exchange and control. This guide demonstrates how to implement Modbus TCP communication with Arduino and ESP32 based PLCs as both master and slave devices.

It is important to note that the Ardbox does not provide Ethernet communication and, therefore, does not support Modbus TCP. However, other Arduino and ESP32 based PLC families like M-Duino and ESP32 14 PLC are fully equipped for Ethernet communication, enabling Modbus TCP functionality.

In this tutorial, we cover the necessary hardware and software setups, including how to configure the devices and write the Modbus TCP master and slave programs using the Arduino IDE and the Industrial Shields Boards. By following this guide, you'll gain a clear understanding of Modbus TCP communication and its implementation in industrial PLC systems.

For more in-depth information about Modbus TCP, check out our Modbus Course.

Requirements

Hardware

• 1 x ​Arduino / ESP32 based PLC (Modbus Master)
• 1 x Arduino / ESP32 based PLC or device with Modbus (Modbus Slave)
• Power supply (12 - 24V)
• B or micro B type cable, to program the Arduino / ESP32 based PLC
• Ethernet cable

Software

• Arduino IDE
• ​Industrial Shields Boards
• Modbus Library

Implementation

Hardware setup

Firstly, power the PLC between 12 and 24V and connect the devices with an Ethernet cable.

Software implementation

Master

In order to program the Modbus Master PLC, follow these steps:

1. Navigate to File > Examples > Modbus or File > Examples > Tools40 > Modbus, and select one of the Modbus TCP examples. These examples demonstrate various Modbus functionalities.

2. Select your Board and Model according to your PLC:

• For M-Duino PLC Family: Tools > Board > Industrial Shields AVR Boards > M-Duino [Extension] family and Tools > Model > M-Duino [Module]
• For ESP32 PLC Family: Tools > Board > Industrial Shields ESP32 Boards > ESP32 PLC Family and Tools > Model > ESP32 PLC [Module]
• For ESP32 PLC 14: Tools > Board > Industrial Shields ESP32 Boards > 14 IOS PLC Family

3. Set up the configurations to configure the Ethernet:

• MAC: Specify a MAC address for the master device.
• IP: Assign a static IP address to the master device.

And make sure that the following configurations are the same as in the slave device:

• Slave IP: The static IP of the slave device.
• Slave port: Default is often port 502, the standard port for Modbus TCP.

4. Finally, upload the sketch at Sketch > Upload.

API Reference

Modbus provides multiple function codes (FC) to read and write the different coils and registers. Our library provides some functions to send messages using the different function codes. These are the functions available:

readCoils(slave, addr, quantity);

readDiscreteInputs(slave, addr, quantity);

readHoldingRegisters(slave, addr, quantity);

readInputRegisters(slave, addr, quantity);

writeSingleCoil(slave, addr, value);

writeSingleRegister(slave, addr, value);

writeMultipleCoils(slave, addr, values, quantity);

writeMultipleRegisters(slave, addr, values, quantity);

Slave

In case of using a PLC for the Modbus Slave device, follow these steps:

1. Navigate to File > Examples > Modbus or File > Examples > Tools40 > Modbus, and select the Modbus TCP Slave example code.

2. Select your Board and Model according to your PLC as with the master.

3. Make sure that the baudrate, duplex mode and serial communication settings are the same as in the master device.

4. The Modbus TCP Slave code is an example for an M-Duino 21+, this means that the pin mapping will need to be modified in case of using another PLC. Check our Modbus Course for further information.

4. Finally, upload the sketch at Sketch > Upload.