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A groovy modbus library

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libmodbus is a free software library to send/receive data with a device which respects the Modbus protocol. This library can use a serial port or an Ethernet connection.

The functions included in the library have been derived from the Modicon Modbus Protocol Reference Guide which can be obtained from

The license of libmodbus is LGPL v2.1 or later.

The official website is The website contains the latest version of the documentation.

The library is written in C and designed to run on Linux, Mac OS X, FreeBSD, Embox, QNX and Windows.

You can use the library on MCUs with Embox RTOS.


You will only need to install automake, autoconf, libtool and a C compiler (gcc or clang) to compile the library and asciidoc and xmlto to generate the documentation (optional).

To install, just run the usual dance, ./configure && make install. Run ./ first to generate the configure script if required.

You can change installation directory with prefix option, eg. ./configure --prefix=/usr/local/. You have to check that the installation library path is properly set up on your system (/etc/ and library cache is up to date (run ldconfig as root if required).

The library provides a libmodbus.pc file to use with pkg-config to ease your program compilation and linking.

If you want to compile with Microsoft Visual Studio, you should follow the instructions in ./src/win32/

To compile under Windows, install MinGW and MSYS then select the common packages (gcc, automake, libtool, etc). The directory ./src/win32/ contains a Visual C project.

To compile under OS X with homebrew, you will need to install the following dependencies first: brew install autoconf automake libtool.

To build under Embox, you have to use its build system.


Some tests are provided in tests directory, you can freely edit the source code to fit your needs (it's Free Software :).

See tests/README for a description of each program.

For a quick test of libmodbus, you can run the following programs in two shells:

  1. ./unit-test-server
  2. ./unit-test-client

By default, all TCP unit tests will be executed (see --help for options).

It's also possible to run the unit tests with make check.

To report a bug or to contribute

See CONTRIBUTING document.


You can serve the local documentation with:

pip install mkdocs-material
mkdocs serve