Modbus Plus

You obviously have good reasons wanting to work with Modbus. I still want to ask the question - why Modbus? Why not a more "modern" approach like a fieldbus? (eg Fieldbus Foundation)

Pieter Steenekamp

Because the specification costs $13,500?

On Tue, 06 Mar 2007 14:10:01 +0000, John Devereux proclaimed to the world:

I was going to say that modbus does most of what people need and is simple. I had no idea that you had to pay to get access to fieldbus specs. Surely there are places to find this info without paying. What do you get from your $13K investment?

You should

You will find all the product info and specifications that you need.

Modbus is a serial protocol, it runs on RS232 or multi-drop RS485.

Modbus is a master and slave protocol. There is Modbus ASCII and Modbus RTU.

Modbus TCP is an implementation of Modbus over TCP/IP, seeking to take advantage of TCP/IP where possible. It uses port 502, as 'registered' by IETF.

Modbus Plus started life as a proprietary implementation of Modbus for Modicon's own PLCs. There were chipsets that went with it. Modicon tried to make it universal but did not go far. Although, they started earlier than other fieldbuses, it was soon overrun by CANopen, Profibus and likes... Recently there has been a revival...

But you can find all this information and more at

thanks.

Including Modbus Plus.

thanks.