PLC programmers hate mapping data like I hate washing and cutting vegetables. They’d much rather write code. I’d much rather cook the fine meal. The cooking and eating are the fun part. Mapping the data was one of the issues with integrating EtherNet/IP devices with Rockwell Automation PLCs, like ControlLogix and CompactLogix in the early days. Some scale might want you to send it 100 bytes of data as outputs and 200 bytes of data as inputs. Each one of those bytes mean something, and your job, as the PLC programmer, is to map them and use them in your program. Somehow, for example, you’d have to know that bytes 4-7 are a floating point tare weight. In the (bad) old days, you would get that from a document. Happily, there are now better ways. Now you can use a much improved Electronic Data Sheets (EDS), and something called an Add On Profile (AOP). There are five options, 1. Simple “stub” EDS File Truthfully, you don’t need much of an EDS In fact, you could just do a short, stub EDS and be done with it. You include the basics like vendor name, product name, revision and such, and you’re done. A stub EDS file doesn’t provide anything to RSLogix5000. Your device is simply a generic device and your customer has to enter the IP address and lengths of your Input assembly and Output assembly. RSLogix5000 pretty much ignores it just like the fat kid at the prom. 2. Simple EDS (Rockwell Calls this “Non-Licensed AOP EDS”)If you want a little more than a stub EDS file, you can describe your configuration data, assemblies and other information in the EDS. RSLogix5000 will load your EDS and use it. Here’s what it will do with a simple EDS file: •Allow your customer to choose from a predefined list of connections (combinations of input, output and configuration assemblies) •Expose your generic configuration options like RPI and Multicast/Unicast •Allow your customer to instantiate multiple connections at once (note that you have to manage the data consistency of those multiple connections) 3. Add On Instructions (AOI) A cool feature of RSLogix5000 is the ability to create Add-On Instructions. This mechanism allows you to define your own instruction. You can make an instruction that contains a commonly used set of instructions (or an algorithm) and use it as one instruction. This means that you could create an AOI that knows how your Input Assembly should be decoded and how to assemble your Output Assembly. Not a perfect solution, but not bad either. 4. EDS With Licensed Key (Rockwell’s “Licensed EDS AOP”)If you want to get more sophisticated, and give your customer the ability to access the items in your I/O Assemblies as individual tags, you’ll want the Rockwell Automation Licensed AOP. You have to go to Rockwell, get their blessing and a special hashtag for your device. A PLC programmer can easily access the fields of your I/O assemblies using the names you define. 5. The PLATINUM Option (Rockwell’s Customer EDS AOP)I am calling this the PLATINUM option because it’s the top-of-the-line, most sophisticated integration you can achieve. Rockwell builds special functionality right into RSLogix that can do just about anything. It might be special functionality to do unique configuration, it could launch some other software program, just about anything is possible. You have to be a really close partner of Rockwell to get this level of integration. It’s not for everyone.
John S Rinaldi
John Rinaldi is Chief Strategist, Business Development Manager and CEO of Real Time Automation (RTA). After escaping from Marquette University with a degree in Electrical Engineering, John worked in various jobs in the Automation Industry before once again fleeing back into the comfortable halls of academia. At the University of Connecticut, he once again talked his way into a degree, this time in Computer Science (MS CS). John is a recognized expert in industrial networks and the author of Four books: The Industrial Ethernet Book, OPC UA: The Basics, Modbus: The Everyman’s Guide to Modbus, and his latest, OPC UA - Unified Architecture: The Everyman's Guide to OPC UA.