Is there a good library for dealing with the Modbus protocol in .NET?

Does anyone know of a good (preferably open source) library for dealing with the Modbus protocol? I have seen a few libraries, but I am looking for some people's personal experiences, not just the top ten Google hits. I figure there has to be at least one other person who deals with PLCs and automation hardware like I do out there.

Open to any other materials that might have been a help to you as well...


I have done a lot of communication with devices for the past few years, since I work for a home automation company, but we don't use Modbus. We do communication in a standard and open way using Web Services for Devices(WSD) which is also know as Devices Profile for Web Services(DPWS).

During this time at one point, I did hear of a project called NModbus. It is an open source library for working with modbus. I have not used it, but looking at the site and the changesets on Google Code, it looks pretty active. You may want to give it a look and even get involved in. This is the only library that I have heard of that targets .Net.

Modbus is a very simple protocol to implement. All information you need can easily be found for free on the Internet.

If you choose to implement it yourself, I will be happy to answer any questions you have along the way.

If you choose to go for a modbus master library I would look for:

  • Modbust TCP support.
  • Modbus RTU over TCP/UDP and COM-port.
  • Configurable byte swapping, word swapping
  • Configurable "base" adress so you can choose adress 1 to actually be adress 0 (sounds stupid, but I prefere to always specify adresses the same way they are documented)
  • it must support reading several adresses as a block, but it need to be flexible, some modbus slaves will return error if any adress in the block is unused/reserved).

AdvancedHMI has a drivers package included that's just great for almost anything comms, though it may be a bit heavy if all you want is Modbus. AdvancedHMI is also under active development and has a strong user base.

NModbus seems to be the most likely to have continued development and there are lots of example projects scattered over the internet.

I have liked using this one in the past (Modbus via TCP):

Modbus to a Siemens Logo PLC is a little different. I have an example project I could send upon request.

Have a look at the offering from Colway Solutions They have a unique licensing scheme where you pay for each Modbus function code that you desire to use. Its not free but the pricing seems to be low. I also saw a few ports of the library to some popular microcontrollers and RTOS.

FieldTalk Modbus Library - handles all Modbus functions

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