In the Rockwell Automation world it is common to find applications on Windows or Linux that exchange data with PLCs like ControlLogix and CompactLogix. These applications can be found in all sorts of industries. They typically have some special logic, user interface or a database component that makes it not feasible in an HMI or PLC. Recipe managers are a good example of these types of applications.
In the Rockwell world, this kind of thing is easy to do. It is easy to get a tool, like our EtherNet/IP Tag Client, that can read and write tags in ControlLogix PLC. These tools open a connection to the PLC and read and writes tags whenever needed. Rockwell has made this interface easy to do.
In the Siemens world, it’s not that easy. In fact there are a lot of difficulties. Let’s start with Profinet IO. As you know there are a number of Profinet flavors. There’s CBA, IO and IRT. CBA is virtually obsolete and IRT requires special hardware so let’s take a look at IO.
To have the equivalent functionality that you find in the Rockwell world, you need two things. One, Profinet IO Controller-side software and two a PLC that can be a Profinet IO device. Well, the last time I checked (this changes quickly) there is no IO Controller code that you can get anywhere. No one has it. You can probably get embedded modules from Ixxat, Hilscher and Softing that do Controller side communication but that is awkward. You have to use some other communication mechanism to talk to the embedded module.
What about the S7 PLC? Well, there’s really little help there either. An S7 can not be configured as a Profinet IO device. It just doesn’t work that way. It’s the Controller, not a device.
If you really want to duplicate the functionality that Rockwell has in the Siemens environment you have to use the proprietary S7 code. You can get that from Siemens by special arrangement but it’s not easy. There is also some open source or free software that’s floating around on the Internet.
I’d be wary of that though. If Siemens revs a controller and changes something, it might impact the interface and then what do you do? Hard to know what changed and how to fix it. To which S7s does the change apply? It gets ugly fast. People are doing this now, it’s just a little more precarious.
So, if you have one of these applications that rides on top of a Rockwell PLC and are thinking about doing the same thing for Siemens – note that it’s a bit harder. Not impossible but harder and more precarious.
DISCLAIMER TIME – I live in the Rockwell world about 80% of the time. Siemens is a huge company with a lot of moving parts. If something has been made available that I don’t know about I’ll update this blog and get that information posted. Let me know!