Modbus Over CIP

I don’t think I ever mentioned my integrator friend Milos. Milos is Yugoslavian. At least he was Yugoslavian. He grew up under communism and was lucky to get out when he did.

He’s been in this country doing automation and integration projects for almost 35 years. He’s got to be 70 but looks 50. I’m sure he’ll die while writing ladder.

He’s a smart guy and he’s quite suspicious of governments and all sorts of organizations. You can understand why. When he was young you never knew what the government might do, who was reporting what to them and who might disappear tonight. It was a scary time.

So I saw Milos the other day and right away he hits me with “So, what’s all this nonsense about Modbus over CIP? Why the hell would I want to fool around with that?”. He goes on to tell me that he had a sales guy in the other day who was spouting off on how Milos should combine Modbus and EtherNet/IP. The guy just couldn’t really explain the technical issues or give him a good reason to do it.

So I give him the basic outline as presented by the ODVA and Schneider Electric:

1.       CIP devices (EtherNet/IP really) and Modbus (both RTU and TCP) have huge installed bases.

2.       Both EtherNet/IP and Modbus are open protocols.

3.       By joining forces and seamlessly integrating these technologies they can offer solutions that preserve legacy equipment and provide additional choices to the customer.

Milos likes to get to the nub of things and get there fast. “Stop talking all that gibberish John. What’s all this really mean?”

Well, here’s what’s really going on. Profinet is a huge threat to Schneider and Rockwell. Siemens and the PTO have done an outstanding job marketing Siemens products and Profinet and these guys are threatened by it. So, by combining Modbus and CIP they have an additional mechanism for fighting off this threat. They get to combine the customers and claim huge installed bases.

Technically, I tell him, there are some additional service codes and some special objects that make Modbus devices directly interact with CIP sources devices. It’s an interesting approach but we haven’t implemented it.

To be honest, I had to tell him, we’ve sold CIP software for 12 years now. We’ve got a pretty large installed base and not one, not one single customer, has every called and asked us about getting an upgrade to our software that supports the Modbus Objects and Services.

In reality, everybody that has a Modbus TCP network is doing Modbus TCP. Everybody that is doing RTU is doing RTU. Same with CIP and EtherNet/IP. When they need to mix the data, they use a Modbus to EtherNet/IP gateway like our 460ESMM.

In reality, you have some part of your legacy architecture that is Modbus RTU, some that is Modbus TCP and other parts that are whatever else. There’s little reason to mix the architectures down at the device level. If you need to mix the data, you do it at the controller level.

So, after our discussion Milos and I headed off to this cool little Hungarian restaurant to discuss less controversial stuff like religion and politics. You should hear his thoughts on our government vs. Marshall Tito’s in the 50s and 60s but that’s for another day.