Why do you use Modbus?

I really like the Modbus protocol which is very simple and popular.

I would like to know in which case you find Modbus appropriate or not.

Thanks in advance

modbus

asked Dec 18 '09 at 09:43

See http://controlsoverload.com/questions/19/what-is-your-favourite-on-machine-distributed-i-o-network. Modbus isn't on the list yet!

(Dec 18 '09 at 14:20) Jeremy Sluyters ♦♦

3 Answers:

oldest newest most voted

We use Modbus/TCP in our non-proprietary control system for the following reasons:

Its got an open standard
Its simple
Its quick and easy to set-up
There are lots of freely available client software packages

The downsides of Modbus/TCP (in my opinion) are:

The standard is pretty loose in a few areas, which can lead to problems communicating between different implementations of the protocol
It only supports simple data-types (booleans, integers, floats etc)
Data items are addressed by Modbus address, rather than item name - so you need to make sure that the Master and Slave both know what items live at what address
Related to the point above, Modbus doesn't have a mechanism for synchronising the data ID lists between the Master and Slave - so you have to do it manually.

link

answered Dec 18 '09 at 10:48

Jon Mills
56●2

I used Modbus about 10 years ago in a DOS program written in Pascal to talk to a Modicon PLC. That was the serial version. The advantage was that the spec was available for free.

Now Modbus/TCP is popular and since it's also open, there are lots of 3rd party libraries you can use to connect directly to PLCs without the need for an OPC server. Great for interfacing with a custom data collection system.

link

answered Dec 18 '09 at 10:26

Scott Whitlock ♦♦
635●1●15

Modbus is a very versitile and very cheap communication protocol, especially when trying to tie multiple devices or controllers together in some form of network. There are many limitations when connecting using a RS-232 connection; however, the Modbus/TCP option removes many of those limitations.

I have seen a few different advantages to using the Modbus/TCP protocol in either a Modbus PLC Controller / Modbus Meters / Modbus Management Systems.

You can create a very large Node network on a small budget compared to ethernet or some other protocol. Another useful tool is the designation of the Addresses used in Modbus. If every device is programmed the same, or even if there are slight changes, all you need to know if the register values. When programming an HMI / OPC all you would need to know is the NODE / IP Address and a some type of spreadsheet with the register addresses. You can then program remotely without any problem.

While I don't prefer Modbus over other protocols, I can understand why it is still in use.

link

answered Dec 18 '09 at 17:08

Luis R
208●1●6

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