The ControlLogix Communication Modules

Learn Logix Part 2.4. This article explains the communication modules available for the ControlLogix system and looks in detail at two commonly used communication modules - the 1756-EN2T and 1756-EN2TR EtherNet/IP communication modules.

Learn Logix is a series of articles designed to teach you everything you need to know to work with Rockwell Automation’s Studio 5000 Logix Designer and the Logix 5000 series of PLCs.

In the last part of the series, we learned about the ControlLogix I/O modules and their features. In this part of the series, we’ll look at 1756 communication modules, which are the communication modules for the ControlLogix system.

The ControlLogix system has communication modules available that enable ControlLogix systems to communicate on many common industrial networks including;

  • EtherNet/IP
  • ControlNet
  • DeviceNet
  • FOUNDATION Fieldbus
  • Data Highway Plus
  • Remote I/O
  • HART

Other communication modules, manufactured by third parties, allow ControlLogix systems to communicate with other manufacturers’ PLC systems.

In the rest of this article, we’ll look at the features of one of the most commonly used ControlLogix communication modules — the 1756-EN2T EtherNet/IP communication module.

1756-EN2T EtherNet/IP Communication Module

The 1756-EN2T EtherNet/IP communication module allows ControlLogix modules to communicate on an EtherNet/IP network.

The most important features of the communication module are the status indicators. The 1756-EN2T module has three status indicators.

Let’s look in detail at each status indicator and what it means.

LINK Status Indicator

The LINK status indicator shows if the module is transmitting data on the EtherNet/IP network.

A flashing green LED indicates that data is being transmitted.

NET Status Indicator

The NET status indicator shows the state of the EtherNet/IP port on the communication module.

A solid green LED indicates that the module has an IP address and at least one active connection with another device.

OK Status Indicator

The OK status indicator shows the overall status of the module.

A solid green LED indicates that the module is operating normally.

1756-EN2TR EtherNet/IP Communication Module

Another common ControlLogix communication module is the 1756-EN2TR, which has two Ethernet ports.

The status indicators on this module are similar to the 1756-EN2T. The main difference is that the 1756-EN2TR has two LINK status indicators and no NET status indicator.


In this article, we learned about the ControlLogix communication modules and looked in detail at the features of the 1756-EN2T and 1756-EN2TR EtherNet/IP communication modules.

In the next part of the series, we will learn about the CompactLogix system. If you haven’t already, be sure to subscribe to the mailing list below to be notified when the next part is available.

Update: You can find the next part of the Learn Logix series, The CompactLogix System, here. This article gives an overview of the CompactLogix system and introduces the components that make up the CompactLogix system such as the bus connectors, power supply, and controllers.

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