One of the gratifying opportunities in the life of a control system’s engineer is to successfully upgrade a legacy system to a newer system with more features and capabilities.

We, as automation specialists in general, love to obtain the newest toys (I mean control system equipment) that we can get our hands on.

The latest network equipment, hardware and software make us look forward to getting back to the office on Monday morning. And truth be told, make us hesitant to leave some days.

5582E, Image by: Brandon Cooper

Not So Fast

An experience last year taught me not to always take similar hardware for granted. We were upgrading an Allen Bradley PLC-5 to the ControlLogix platform, the same as we have done many times.

However, I had been using the L7X series of processors and had no issues with communicating to the existing Honeywell system.

But for this particular project, I opted for a new L8XE series Controllogix processor. I thought, “Let’s get the newest one, it’ll be cool….” However, upon installation I ran into a hurdle: our Honeywell Experion Controllers would not perform CIP Reads/Writes with the L8XE processor.

I immediately began technical support calls with both Rockwell and Honeywell to understand the issue. What I found out caused me to back up and punt to an L7X processor until a resolution could be found.

I learned that changes were implemented in the L8XE CIP Security features that are not found in the L7X series of controllers from Rockwell.

Thus, Honeywell would have to make changes in their controller firmware to create compatibility with an L8XE processor.

Catching Up

Since that time, Honeywell has made the needed changes for a C300 processor at R510 or above to communicate with the L8XE processor, however, the C200 will not.

I have tested the C300 as well with R500 and below and it does not communicate via CIP Reads/Writes with the L8XE.

All in all, if you don’t need redundancy and do not have communication constraints with other vendors, the L8XE processor is lightning fast and performs as good as anything out there.

The 1GB port on the processor itself also fits nicely into a capable network. The quad processors handle logic and communications separately, so there is no overhead time slice to configure when trying to balance performance and communications as was with the L7 and below.


I learned in that project that not every product that is similar will work the same or have the same compatibility as the similar product.

When we are talking about cutting edge versus bleeding edge kinds of equipment changes, it always makes good practice to test and verify, even if there is no apparent reason that it would not work as planned.

Written by Brandon Cooper
Senior Controls Engineer and Freelance Writer

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Brandon Cooper


  1. The 1756-L8xE is in many ways differnt to the 1756-L6x and L7x serie. Also in the comming redundant version some features available in the L7x redundant serie won’t work. Also new features in the L8xE won’t work in the redundant version.
    With the L8 serie RTFM or contacting a sales-person is really important.

    • Very true. I’ve had people from Rockwell tell me they should have launched the L8 with a completely different part number because of the amount of differences to the L7 and below. It’s a great product, but there was a learning curve with the unexpected differences.

      • Thank you both for sharing!

        As a self employed blogger and instructor, I don’t get to play with the newest products unless vendors send them in to use on the blog and show, and so far no one at Rockwell has been inclined to send us a demo to use in house 🙁

        So thanks again for sharing!


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