Modbus library for modern C++

Library for high level Modbus frame/packet manipulation, including encoding and decoding, all written in modern C++17.

Additionally, library contains reference TCP and RTU implementation (on Linux only !), that you can use as a starting point for you application ! Until there will some reliable way to test it, it will be treated as such.

More informations for Windows users

If you are interested in Windows RTU implementation, you can look at to pull request: #5 . I am currently unable to merge it, as I do not have required hardware for testing.

Table of content

• Why
• Important Concept
• Possibilities
• Dependencies
• Status
• Installation
• Api

Why

When I was working on my last project and tried to find a good C++ Modbus library (other than Qt) I was unable to find it. That is why I have decided to share my own implementation of Modbus.

Important Concept

This library is mainly for providing Modbus logic. It doesnt aim to have best communication implementation, as it is usually HW-specific. It gives user ability to create Modbus frames using high level api and convert them to raw bytes or show them as string. That is why Modbus Core is OS independent and can be easily used with other communication frameworks, assuming that you compiler supports at least C++17.

Modbus communiaction module is enabled by default and works pretty well on linux. If you are using your own communication, be sure to disable it via cmake variable.

Possibilities

Quick example of what Modbus Core can do:

Code:

#include "MB/modbusException.hpp"
#include "MB/modbusRequest.hpp"
#include "MB/modbusResponse.hpp"

// Create simple request
MB::ModbusRequest request(1, MB::utils::ReadDiscreteOutputCoils, 100, 10);

std::cout << "Stringed Request: " << request.toString() << std::endl;

std::cout << "Raw request:" << std::endl;

// Get raw represenatation for request
std::vector<uint8_t> rawed = request.toRaw();

// Method for showing byte
auto showByte = [](const uint8_t &byte) {
    std::cout << " 0x" << std::hex << std::setw(2) << std::setfill('0')
                << static_cast<int>(byte);
};

// Show all bytes
std::for_each(rawed.begin(), rawed.end(), showByte);
std::cout << std::endl;

// Create CRC and pointer to its bytes
uint16_t CRC = MB::utils::calculateCRC(rawed);
auto CRCptr  = reinterpret_cast<uint8_t *>(&CRC);

// Show byted CRC for request
std::cout << "CRC for the above code: ";
std::for_each(CRCptr, CRCptr + 2, showByte);
std::cout << std::endl;

auto request1 = MB::ModbusRequest::fromRaw(rawed);
std::cout << "Stringed Request 1 after rawed: " << request1.toString() << std::endl;

// Add CRC to the end of raw request so that it can be loaded with CRC check
rawed.insert(rawed.end(), CRCptr, CRCptr + 2);
auto request2 = MB::ModbusRequest::fromRawCRC(rawed); // Throws on invalid CRC
std::cout << "Stringed Request 2 after rawed: " << request2.toString() << std::endl;

Output:

Stringed Request: Read from output coils, from slave 1, starting from address 100, on 10 registers
Raw request:
 0x01 0x01 0x00 0x64 0x00 0x0a
CRC for the above code:  0xfd 0xd2
Stringed Request 1 after rawed: Read from output coils, from slave 1, starting from address 100, on 10 registers
Stringed Request 2 after rawed: Read from output coils, from slave 1, starting from address 100, on 10 registers

Dependencies

Library core is dependency free - except for C++ standard library.

For communication module, you may need:

• libnet - only for tcp communication (not needed if communication is disabled)

STATUS

Currently Modbus Core is fully functional and (I belive) it doesn't have any bugs.

Modbus Communication is working currently only for linux, it works well on TCP and Serial (tested on raspberry pi).

How to learn Modbus ?

Just use Simply modbus.

How to install it ?

Using CMAKE and git

First go to directory that will contain this library.

git clone https://github.com/Mazurel/Modbus
git submodule update --init --recursive # Fetch submodules (google tests)

Then add to your CMakeLists.txt

add_subdirectory(Modbus)
target_link_libraries(<your exec/lib> Modbus)

You should be able to use library.

NOTE If you are on other os then gnu/linux you should disable communication part of modbus via cmake variable MODBUS_COMMUNICATION.

API

API documentation is generated using Doxygen and it is available online under this link. If you want, you can also generate it yourself !