Skip to main content
Donate to the Python Software Foundation or Purchase a PyCharm License to Benefit the PSF! Donate Now

Easy-to-use Modbus RTU and Modbus ASCII implementation for Python

Project description

Build Status Documentation Status PyPI page link Test coverage report

Easy-to-use Modbus RTU and Modbus ASCII implementation for Python.

Web resources

Other web pages:

Obsolete web pages:


MinimalModbus is an easy-to-use Python module for talking to instruments (slaves) from a computer (master) using the Modbus protocol, and is intended to be running on the master. Example code includes drivers for Eurotherm and Omega process controllers. The only dependence is the pySerial module (also pure Python).

This software supports the ‘Modbus RTU’ and ‘Modbus ASCII’ serial communication versions of the protocol, and is intended for use on Linux, OS X and Windows platforms. It is open source, and has the Apache License, Version 2.0.

Tested with Python 2.7, 3.2, 3.3 and 3.4.


Release 0.7 (2015-07-30)

  • Faster CRC calculation by using a lookup table (thanks to Peter)
  • Handling of local echo (thanks to Luca Di Gregorio)
  • Improved behavior of dummy_serial (number of bytes to read)
  • Improved debug messages (thanks to Dino)
  • Using project setup by the cookie-cutter tool.
  • Reshuffled source files and documentation.
  • Moved source to Github from Sourceforge.
  • Moved documentation to
  • Using the tox tool for testing on multiple Python versions.
  • Using Travis CI test framework
  • Using code coverage measurement framework
  • Added support for Python 3.3 and 3.4.
  • Dropped support for Python 2.6.

Release 0.6 (2014-06-22)

  • Support for Modbus ASCII mode.

Release 0.5 (2014-03-23)

  • Precalculating number of bytes to read, in order to increase the speed.
  • Better handling of several instruments on the same serial port, especially for Windows.
  • Improved timing for better compliance with Modbus timing requirements.

Release 0.4 (2012-09-08)

  • Read and write multiple registers.
  • Read and write floating point values.
  • Read and write long integers.
  • Read and write strings.
  • Support for negative numbers.
  • Use of the Python struct module instead of own bit-tweaking internally.
  • Improved documentation.

Release 0.3.2 (2012-01-25)

  • Fine-tuned for smoother installation.
  • Improved documentation.

Release 0.3.1 (2012-01-24)

  • Improved requirements handling in
  • Adjusted not to include doc/_templates
  • Adjusted RST text formatting in README.txt

Release 0.3 (2012-01-23)

This is a major rewrite, but the API is backward compatible.

  • Extended functionality to support more Modbus function codes.
  • Option to close the serial port after each call (useful for Windows XP etc).
  • Diagnostic string output available (for support).
  • Debug mode available.
  • Improved __repr__ for Instrument instances.
  • Improved Python3 compatibility.
  • Improved validity checking for function arguments.
  • The error messages are made more informative.
  • The new example driver omegacn7500 is included.
  • Unit tests included in the distribution.
  • A dummy serial port for unit testing is provided (including recorded communication data).
  • Updated documentation.

Release 0.2 (2011-08-19)

  • Changes in how to reference the serial port.
  • Updated documentation.

Release 0.1 (2011-06-16)

  • First public release.

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, size & hash SHA256 hash help File type Python version Upload date
MinimalModbus-0.7.tar.gz (102.9 kB) Copy SHA256 hash SHA256 Source None (121.1 kB) Copy SHA256 hash SHA256 Source None

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN SignalFx SignalFx Supporter DigiCert DigiCert EV certificate StatusPage StatusPage Status page