Should ControlLogix Processors Come With Ethernet On-board?

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In Monday’s article here we discussed what appeared to be the premature outing of a new ControlLogix 1756-L85E processor with built-in 1GB Ethernet port.

That news brought up the question, do ControlLogix users want processors with built-in Ethernet?


At first glace, the obvious answer would be a resounding “YES!”

But, could there be any downsides to having your Ethernet port built-in?

With that question in mind, today we look at three things that may determine if having an integrated Ethernet port is right for you.

1) Cost

Typically, having items integrated is less expensive then buying them separate.

However, we don’t actually know yet if the cost of the L85E is less than an L75 and an EN2T combined.

Will the L85E have more features and functions that the L75, thereby making the processor more expensive?

Or, is the L85E the same as the L75 but with an embedded Ethernet port similar in features to the EN2T, and thereby less expensive?

2) Performance

The current batch of 1756 Ethernet modules are pretty beefy cards, sporting sizable heat sinks and are seemingly much heavier than older models.

With that said, is it really possible that Rockwell could squeeze all the same performance of today’s newer 1756 Ethernet modules, as well as 1GB Ethernet support, into the same slot as a next generation processor?

Or perhaps, in order to get both processor and Ethernet card into one slot was something left out?

1756-L85E Leaked

3) Commonality

Today, many ControlLogix systems utilize multiple Ethernet communication modules, and system designers typically use the same Ethernet module throughout the system to insure commonality of features and function.

However, in future systems if one of the Ethernet ports is built-in to the processor will this mean sacrificing commonality of capabilities between all Ethernet communications ports?

So, what do you think? Should ControlLogix processors come with Ethernet ports, and are any of the above concerns valid?

Let us know what you think by sharing your thoughts in the “Leave a reply” form at the bottom of this page.


Shawn Tierney
Automation Consultant
Insights In Automation

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Legacy Comments

  1. I think you’ve brought up a great question. This is something that is still weird to me in the AB world. I spend most of my time using Siemens where everything comes with an ethernet or two standard. What I can’t figure out is what are EN2Ts or ENBTs doing that everyone else is not. I can get a 4 port layer 3 switch with an onboard processor for half the cost/weight/size. Any insight into this would be helpful and might help with my ongoing disdain towards AB.

    • Good afternoon Richard,

      Thank you very much for your comments.

      I don’t think I can help with your opinion of Rockwell, but I can share my opinion for the reason why ControlLogix systems today include separate communication modules.

      Back in 1985 Rockwell began seriously (imo) integrating networks into their PLC’s with the release of the PLC-5 with multiple DH+ and RIO networks built-in.

      However, when the ControlLogix released in 1998 not many Allen-Bradley customers had adopted Ethernet for control, and many were still using a mixture of one or more of the following: DH+, RIO, ControlNet, and DeviceNet.

      So to avoid having several different processors (imo) Rockwell released the processors and network cards as separate modules, allowing customer to buy the right combination to meet their needs.

      Actually, the network modules came out before the processors, and they’re totally independent. This means you can actually route from one communication module through another without a processor in the rack.

      In many plants that was very popular, and I personally know of dozens of plants that have 6 or more dual DH+ modules and one Ethernet module in a 1756 chassis being used as a plant-wide legacy PLC bridge.

      That said, today it seems like most all systems use Ethernet, and it also seems Rockwell knows this as they are on the cusp of releasing a new line of ControlLogix processors with an integrated Ethernet port, like has been available on the CompactLogix, MicroLogix, SLC-500 and PLC-5 for many years now.

      More info here:


      Shawn Tierney

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  2. Allowing access to the chassis to perform its intended function as a gateway or “bridge” is what was the reasoning for Rockwell to come out with the 1756-ENET…later 1756-ENBT modules as well as modules for DH+/Remote I/O,ControlNet, etc.

    Having the Ethernet built-in to the front of the ControlLogix controller (L8-series) is a good thing becase now it frees up one slot that might have been used in the past for an ENBT/EN2T module to be used for HMI/Programming while a 2nd ENBT was used for Remote I/O over Ethernet. Now, a single ENBT/EN2T can be used for the Remote I/O over Ethernet.

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