which one of the communication protocols are open source (modbus, modbus plus, profinet, profibus, foundation fieldbus, CANOPEN. which are main companies developing products using these technologies?

 

You have to differentiate between the protocol definition and the implementation.

The definition, or protocol standard, can be 'open' in the sense that you have not to pay for it. and you can implement it without paying any royalties to the standardization body or the license owner
(if there is one.) CANopen is such an 'open' standard.

The source code of such a protocol implementation is a different thing. But take care. There are different definitions on this topic:
http://en.wikipedia.org/wiki/Open-source_software

Regards
Heinz

 

In what I do, I see less modbus and profibus than I did before. CanOPEN, DeviceNet (A-B version of CanBus), and TCP/IP are becoming more common.