DF/1 is now entering middle age. I don’t know if there is anyone left who remembers its birth. If there is they would have to be in their 60s or 70s (Thank God I’m not that old). I’d bet they’d be retired by now. People of that era had a sweet pension deal at Allen-Bradley when it was still owned by the Bradley family.
But let’s stop and catch you all up before I go on.
DF/1 is one of those terms that a lot of people use but few really know. It’s used to talk about the protocol for moving data in and out of Allen-Bradley PLCs, some drives and a few other products.
In actuality it’s really just a link layer protocol. That means that its job is to move a message from point A to point B. Nothing more. Nothing less. It has absolutely nothing to do with the contents of the message. Just move it from here to there.
Where most people go wrong is that they assume that DF/1 also includes the messaging that allows a user to write a File (N7:200 or the like) and read a file. In actuality that messaging is something called PCCC which has a number of meanings. The meaning for PCCC that I like is Programmable Controller Command and Control language.
PCCC is the protocol that allows for reading and writing all the different kinds of file structures that you find in the various types of Allen-Bradley PLCs. PCCC is actually encapsulated in a DF/1 link layer message. So the two of them work together. A user application builds a PCCC message and then hands it off to the DF/1 layer who moves it from here, wherever that is, into the PLC.
At this late date, two thousand and fourteen, PCCC and DF/1 are still very much around and very much integral to the communications of Allen-Bradley PLCs. DF1 and PCCC are as important to the operation of RA PLCs as is EtherNet/IP, DeviceNet or anything else.
Why is that?
It’s reliable. The code is done. It’s already there and tested. There’s an infrastructure built around it that is comfortable and soothing. DF/1 and PCCC are kind of like those old slippers you have in the closet or that old work shirt you put on to putter around the garage. It just feels good.
I bring this up today because I had a conversation with a customer this morning about this. He’s got an old system that not only used DF/1 they modified how it works. Talk about creating a disaster for the future – that’s exactly what they did.
They need to take that old, modified DF/1 code that is generated by this old legacy system they don’t want to touch and convert the messages it sends out, the modified DF/1, into messages that a MicroLogix can understand, standard DF/1. Of course, they really mean PCCC but I didn’t tell them that. I let them call it DF/1.
It’s not a hard project. Just a day or so for us in the customers offices and we’ll do a gateway for them. We do a lot of these kind of “get me out of this jam” kinds of projects. It’s one of the things I really enjoy about the job.
So, to answer my original question. Will DF/1 ever die? The answer is an emphatic NO. There are probably 20 million Allen-Bradley PLCs in the world today. It will take another 75 years before they are all obsoleted and trashed. So, DF/1 (and PCCC) is going to be with us for a long, long time.
And that’s OK by me. It’s an old friend and I would miss it if it was gone.