libmodbus - C++ Modbus Protocol Implementation

A comprehensive C++ implementation of the Modbus protocol supporting RTU, ASCII, and TCP variants. The library provides a clean, modern C++ interface for building Modbus servers and clients with full compliance to Modbus specifications.

🚀 Key Features

Complete Function Code Support: All standard Modbus function codes (FC 01-08, 15-16)
Multiple Transport Protocols: RTU (complete), ASCII and TCP (planned)
Standards Compliance: Full compliance with Modbus Application Protocol V1.1b3
Modern C++ Design: C++17 compatible with RAII principles and type safety
Configurable Data Model: Supports standard and custom Modbus limits
Comprehensive Testing: Full unit test coverage with Google Test
Header-Only Design: Easy integration into existing projects
Cross-Platform: Works on Windows, Linux, and macOS

📋 Supported Function Codes

Code	Function	Status
01	Read Coils	✅ Complete
02	Read Discrete Inputs	✅ Complete
03	Read Holding Registers	✅ Complete
04	Read Input Registers	✅ Complete
05	Write Single Coil	✅ Complete
06	Write Single Register	✅ Complete
08	Diagnostics	✅ Complete
15	Write Multiple Coils	✅ Complete
16	Write Multiple Registers	✅ Complete

🏗️ Architecture

The library is built around several key components:

ModbusDataModel: Stores all four types of Modbus data (coils, inputs, registers)
ModbusCommand: Command pattern implementation for function codes
ModbusFrame: Protocol Data Unit and transport-specific frames
ModbusBaseServer: Abstract server base with protocol-specific implementations
Checksum: Utilities for CRC-16 and LRC calculations

📖 Documentation Sections

🚀 Quick Start

Building the Library

mkdir build && cd build
cmake ..
make

Basic Server Example

#include "libmodbus.hpp"

int main() {
    // Create RTU server
    ModbusRtuServer server;

    // Initialize some data
    server.data.writeCoil(0, true);
    server.data.writeHoldingRegister(0, 0x1234);

    // Process a request (normally from serial port)
    std::vector<uint8_t> request = {0x01, 0x01, 0x00, 0x00, 0x00, 0x08, 0x3D, 0xCC};
    auto response = server.process(request);

    return 0;
}

📦 Installation

Prerequisites

C++17 compatible compiler
CMake 3.10 or higher
Google Test (included as submodule)

Clone and Build

git clone --recursive https://github.com/shishir-dey/libmodbus.git
cd libmodbus
mkdir build && cd build
cmake ..
make

Running Tests

make test

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

📞 Support

For questions, issues, or suggestions, please open an issue on the GitHub repository.

Version: 1.0

Last Updated: Jun 20, 2025