Introduction to Allen-Bradley/Rockwell Automation PLCs

In this post, we compare the various families of PLCs available from Rockwell Automation including the Micro800, CompactLogix, and ControlLogix family of PLCs to understand when each family of PLC can be used in automation applications.

In a previous post, I explained what a PLC is, what components make up a PLC, and what PLCs are used for. In that post, I also mentioned that automation manufacturers tend to sell multiple families of PLCs to serve different market needs. In this post, I will expand on that idea by introducing and explaining the PLC families sold by Rockwell Automation under the Allen Bradley brand.

By the end of this post, you will;

  • Know the PLC families offered by Rockwell Automation,
  • Know what type of applications each controller family is used for,
  • Understand the positioning of each controller family relative to each other

Let's start with an overview of the portfolio of controllers manufactured and sold by Rockwell Automation.

The Rockwell Automation Portfolio of Controllers

The main controller families in the Rockwell Automation portfolio of controller families are;

The Micro800 family of controllers, which is a series of micro PLCs designed with basic functionality to control simple machines.

The CompactLogix family of controllers, which is a series of mid-range PLCs designed to control standard machines with some complex functions like motion control.

The ControlLogix family of controllers, which is a series of high-end PLCs designed to control complex systems with thousands of points of I/O and specialty functions like redundancy.

The AADvance and Trusted family of controllers, which is a series of specialist controllers that are strictly used for Process Safety applications. These controllers are outside the scope of this post but are mentioned in the overview because they are often included in Rockwell Automation literature.

Let's take a look at each family of controllers in more detail.

The Micro800 Family of Controllers

Micro800 Family of Controllers (and more)

The Micro800 range of PLCs are a series of micro PLCs designed to be low cost and suitable for small, standalone machines. These are economical PLCs with limited functionality.

The PLCs in the range are available in different form factors, with a different number of embedded I/O points, and a range of different features to address different requirements.

The PLCs in this family are grouped together because they share a common programming environment, common accessories, and common plug-in modules. Because the Micro800 family can be expanded with accessories and plug-in modules, machine builders have some capacity to customize their Micro800 system and buy just enough control to get the job done.

Connected Components Workbench

Connected Components Workbench Logo

As I mentioned previously, all of the Micro800 PLCs are programmed in a common design environment called Connected Components Workbench, or CCW for short. This is a single software that is used to configure component devices like Variable Frequency Drives, program Micro800 PLCs, and to create visualization applications for PanelView800 HMIs.

Connected Components Workbench is completely free to download and use. You can grab a copy from the Rockwell Automation website.

My free introduction to PLC programming and my flagship course that shows how to develop automation projects from scratch both use Connected Components Software because it includes a Micro800 Simulator. This simulator let's you test your PLC projects without buying any hardware, using a simulated PLC.

Plug-in Modules

Micro800 Plug-In Modules

The functionality of Micro800 PLCs can be extended by using plug-in modules. These plug-in modules extend the functionality of the Micro800 PLCs without impacting the footprint of the controller.

There are plug-in modules available for analog I/O, communication protocols, backup memory modules, and more. A complete list of plug-in modules is available from Rockwell Automation.

Plug-in modules can only be used with Micro820, Micro830, and Micro850 controllers. Plug-in modules are not compatible with Micro810 controllers.

Expansion I/O

Expansion I/O Modules for Micro850 PLCs

Micro850 and Micro870 PLCs can be extended even further with side-mounted 2085 Expansion I/O modules. These modules click into the side of a PLC to form one large brick.

The 2085 expansion I/O is more advanced and of higher IO density than the plug-in I/O modules. For these reasons, they are also more expensive than plug-in I/O modules.

2085 expansion I/O modules are only compatible with Micro850 and Micro870 PLCs. They cannot be used with Micro810, Micro820, or Micro830 PLCs.

A Note on the Micro810 PLC

Micro810 with Plug-In Display

The Micro810 PLC is a bit of an outlier in the Micro800 family. These PLCs are more like smart relays with high current outputs that can be programmed like a micro PLC.

The Micro810 does not support the plug-in modules used by the rest of the Micro800 range. Instead, the Micro810 has an optional plug-in LCD screen. This screen can be used to visualize the current status of the device and as a means to configure a Micro810 PLC without using Connected Components Workbench. In the image above, you can see a Micro810 with the LCD screen installed.

Engineering Tools

The focus on the Micro800 family of PLCs is on making things easier - the PLCs are simple to work with, CCW makes it easy to program PLCs, configure devices, and create HMI applications in one environment. To continue this idea of making things easier, Rockwell Automation have developed some engineer tools for the Micro800 family that makes it easier to build common machines (or at least to reduce the machine development time).

Connected Components Accelerator Toolkit (CCAT)

The Connected Components Accelerator Toolkit (abbreviated as CCAT) is a comprehensive design tool that;

  • Simplifies the selection of components for a machine,
  • Imports PLC code for common functions,
  • Automatically creates electrical and other drawings,
  • Provides sample screens for PanelView800 HMIs,
  • Generates a detailed bill of materials for a machine

With this tool, Rockwell Automation claims that OEMs can reduce the time it takes to design, develop, and commission simple machines by up to 50%.

You can learn more about the Connected Components Accelerator Toolkit here or download the application here.

Sample Code

Rockwell Automation also provides sample code to help OEMs to solve specific application easily. There are two types of samples available from Rockwell automation;

  • Solutions, provide the design for a complete machine including code, visualization, bill of materials, and a whitepaper. You can find the collection of Micro800 solutions here.
  • Sample Code, provides User Defined Function Blocks that can be used in your Micro800 PLC programs to provide a specific function like communication over a Modbus network. You can find the collection of Sample Code UDFBs here.

Summary of Micro800 Systems

The Micro800 family of PLCs is a set of small, economical PLCs designed to control simple machines and processes. Micro800 PLCs are economical because they provide limited functionality and because the Micro800 development environment, Connected Components Workbench, is free to download and use.

The Micro800 family of PLCs can be extended with plug-in modules and, in the case of the Micro850 and Micro870, expansion I/O modules. These plug-in modules allow a Micro800 user to buy exactly the amount of control that they need for their application.

To help get new users up an running with Micro800 systems, Rockwell provides some engineering tools including the CCAT design tool, complete designs for simple machines, and sample code to handle basic automation tasks.

Altogether the Micro800 family of PLCs are great for OEMs who want to keep the costs for their standard machines low and for people who want to learn about PLC programming without spending thousands on hardware and software to learn.

Logix 5000 Controller Portfolio Overview

The next two PLC families that we will talk about are the CompactLogix and ControlLogix family of PLCs. Where the Micro800 family of PLCs is designed for small and micro sized applications, the CompactLogix and ControlLogix PLCs are designed to tackle mid-size to very large and complex automation tasks.

These PLC families are part of Rockwell Automation's Logix 5000 platform, which is an essential component in Rockwell Automation's Integrated Architecture portfolio of products. Before we talk about the CompactLogix and ControlLogix family of PLCs, let's take a minute to look at the Logix 5000 platform and the Integrated Architecture portfolio of products.

Before we move on, I want to mention that if you are interested in learning how to program Logix 5000 controllers using Studio 5000 Logix Designer, you should check out my course PLC Programming with Studio 5000 Logix Designer where I show you how to develop and test your first project in Studio 5000 Logix Designer.

Logix 5000 and Integrated Architecture

Rockwell Automation's Integrated Architecture is a portfolio of advanced control products, which include Logix 5000 PLCs like the CompactLogix and ControlLogix families of PLCs. Integrated Architecture also includes I/O modules, servo drives, variable frequency drives, and HMIs for visualization. These products are part of the Integrated Architecture platform because they can easily be integrated together to control a variety of automation applications.

Integrated Architecture products and Logix 5000 controllers are considered to be advanced automation products because they offer;

Multi-Discipline Control

This means that a single controller can be used to control multiple automation disciplines including standard control, motion control, safety control, and process control. In the past, each of these disciplines would have required a dedicated controller, programmed with dedicated software. Each of these controllers would then have to be integrated into a single system. With Logix 5000 controllers, you only need a single controller, programmed in a single development environment to control all automation disciplines.


Logix 5000 controllers and Integrated Architecture products can be used to control small to very large automation systems. This means that OEMs can have a single control architecture that scales up and down depending on the application that they are working on. Regardless of the size of the application, a common design environment is used to program the PLCs and configure the devices.

Advanced Industrial Networking

Logix 5000 PLCs and Integrated Architecture products are design to communicate using EtherNet/IP. This is a real time control network that utilizes standard, unmodified Ethernet and Internet Protocol. The benefit of EtherNet/IP is that it is "IT Ready", meaning that devices communicating over EtherNet/IP can easily be connected to enterprise networks to be integrated with ERP and MES systems.

Studio 5000 Logix Designer

Studio 5000

All Logix 5000 controllers are programmed in a common design environment called Logix Designer. Logix Designer is part of the Studio 5000 Design Environment, which also includes tools to;

Older versions of Studio 5000 Logix Designer were called RSLogix 5000. When working with older engineers, you may still hear them refer to Logix Designer by this name. Regardless of how you choose to call it, remember that Studio 5000 Logix Designer is the software that you need to use to program Logix 5000 PLCs.

The CompactLogix Family

The CompactLogix Family of PLCs

As I mentioned already, the Logix 5000 platform is made up of two families of PLCs. The first family of PLCs that we will talk about is the CompactLogix family.

The CompactLogix is a set of mid-range PLCs, that are higher performance than Micro800 PLCs but are still not as advanced as ControlLogix PLCs.

All of the PLCs in the CompactLogix family are rackless PLCs. This means that, unlike the ControlLogix family, they do not have a chassis.

In a CompactLogix system, the PLC typically sits on the left of the rack and expansion modules are added to the right of the PLC. An electrical connection is made between the expansion modules and the controllers using a dedicated connector.

In newer generations of CompactLogix PLCs, there is an integrated EtherNet/IP port on the PLC. In older CompactLogix PLCs, there is no integrated EtherNet/IP port. For these older PLCs to communicate on an EtherNet/IP network, a dedicated EtherNet/IP communication module was required in the CompactLogix rack.

CompactLogix PLCs

CompactLogix Positioning

The CompactLogix family contains a range of different PLCs with different features and functions.

In terms of functionality, the CompactLogix 5370 L1 and 5370 L2 have the least user memory available and, when the integrated motion version is selected, can control a limited number of motion axes. These PLCs are unique in the family because they have embedded I/O. Other CompactLogix PLCs require expansion I/O modules. Both CompactLogix L1 and L2 PLCs also support expansion I/O modules to increase the number of I/O points available.

The CompactLogix 5370 L3 and CompactLogix 5380 PLCs have more features than the L1 and L2 models. These PLCs have more user memory available, can control more axes of motion, and certain variations of these PLCs support Integrated Safety. CompactLogix PLCs that have Integrated Safety are called Compact GuardLogix PLCs.

Each CompactLogix PLC uses a different type of I/O module for expansion I/O. The CompactLogix 5370 L1 PLC uses 1734 Point I/O for local expansion I/O. The CompactLogix 5370 L2 and L3 PLCs use traditional 1769 Compact I/O modules for expansion I/O. Finally, the newer CompactLogix 5380 controller uses Compact 5000 High Performance I/O modules for local expansion I/O.

When choosing a CompactLogix PLC, I always consult the Rockwell Automation CompactLogix Selection Guide to double check which controllers have all of the features and functions that I require for an application. You can find that document here.

The ControlLogix Family

The ControlLogix PLC System

Rockwell Automation's most advanced PLC family is the ControlLogix family of PLC. The ControlLogix family of PLCs are chassis based PLCs typically do not have integrated communication or I/O. The latest generation of ControlLogix controllers are an exception to this rule - they come with an integrated EtherNet/IP port.

In a ControlLogix system, modules are installed in a chassis which provides an electrical connection between the modules and the PLC. A power supply, located on the left of the chassis, provides power to all of the modules installed in the chassis. The ControlLogix system is designed to be flexible in terms of PLC placement - a controller module can be installed in any slot in the chassis and a single chassis can contain multiple controllers.

The ControlLogix system can be expanded with specialty modules that are not available for CompactLogix PLCs. These include modules for redundancy in critical applications, a Model Predictive Control module for advanced tuning of continuous process applications, and a Network Security module. There are also modules produced by third parties to provide functionality that Rockwell Automation doesn't provide directly.

Most components in the ControlLogix family, like controllers, I/O modules, and communication modules, have a catalog number that begins with 1756. ControlLogix controllers have part numbers with the constant 55 followed by two variable numbers. These variable numbers indicate the model generation of the controller and the specific model of the controller respectively. For example, a 1756-5585, is an 8th generation ControlLogix controller.

Just like with CompactLogix systems, Rockwell Automation publishes a ControlLogix Selection Guide that explains the difference between the PLCs in the ControlLogix family.

ControlLogix XT

ControlLogix XT Controllers

Many ControlLogix modules have a specialized version called XT versions. XT is short from eXTreme environments. The main difference between the standard and XT version of a module is that XT modules can operate in a wider temperature range and have improved protection against corrosive environments. There are many design modifications in XT modules that make these technical differences possible such as a larger spacing between modules in the chassis for improved airflow and conformal coating of the electronics to improve their resistance to corrosive environments.

Relative Positioning of Rockwell Automation PLC Families

As we reach the end of this post, you should understand the difference between the three main PLC families offered by Rockwell Automation and their capabilities.

At the low-end, is the Micro800 family of controllers. These PLCs are designed to be economical for simple automation processes. They are a great starter PLC for anyone who wants to learn PLC programming independently without spending a lot of money.

For mid-sized automation systems and more complex machines, there is the CompactLogix family of PLCs. These PLCs are scalable with communication and expansion I/O modules and are capable of multi-discipline control with models available for motion control and safety control as well as standard logic execution.

Finally, the ControlLogix family of PLCs is Rockwell Automation's flagship product. These PLCs are suitable for large systems with a lot of I/O, motion control, and safety control. The ControlLogix system can be extended with specialty modules to provide functionality not available from other PLC systems like redundancy for critical applications.

A Note on Older Rockwell Automation PLC Families

The PLC families discussed here are Rockwell's contemporary portfolio of PLC families.

Rockwell Automation also has already PLC families that are not promoted anymore or are completely obsolete but still have a large install base in factories throughout the world. These older PLC families include;

The MicroLogix Family

The MicroLogix family was the previous generation of micro PLCs from Rockwell Automation. Most MicroLogix PLCs are now obsolete but some models are still sold and supported.

MicroLogix will eventually be completely replaced by the Micro800 family of PLCs.

The SLC Family

MicroLogix PLCs share a programming software with another family of PLCs called SLC, or Small Logic Controller. These PLCs were designed as mid-range PLCs to handle the same applications as CompactLogix PLCs are used for today.

Most SLC models are now obsolete.

The PLC-5 Family

Finally, there is the PLC-5 family of PLCs which were introduced in the 1980's and only recently made obsolete. This was a very successful series of PLCs and is one of the products that put Rockwell Automation on the map as an automation vendor.

There are still may factories in the world running on PLC-5 PLCs, although those older systems should be migrated to the ControlLogix families in the near future. This is because PLC-5 parts will become harder and harder to source.

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