L23-Serial-FiIn today’s article I walk you step-by-step through how to configure RSLinx to communicate to a CompactLogix processor’s serial port using a serial cable and USB to Serial converter.

Part 1 – Reviewing needed cables, and finding PC comm port number

Step 1) A-B Cables, or low cost variant from Amazon

If you already have a bag full of Allen-Bradley cables, for this exercise you’ll need to grab the following two:

However, if you are on a budget, below are two low cost equivalents you can pickup on Amazon.com:

As an alternative to the above Null modem cable, you may find it more advantages to pickup the below standard serial cable and a Null Modem adapter:

Step 2) Finding the com port for your USB to Serial device

Once you’ve installed the software for your USB to Serial converter, and plugged that cable in, you’ll need to find out what com port Windows has assigned to it.
To do this, first open device manager:

  • A quick way to get to Device Manager is to right click on “My Computer” and select “Properties”

My-Computer-PropertiesYou can also open Device Manager by launching the “System” applet from Windows Control Panel.

Control-Panel-SystemOnce Device Manager is open, scroll down and expand “Ports” and you should see your device listed as one of the available ports


Part 2 – Configuring RSLinx Classic

Step 1) Launch RSLinx Classic and open “Configure Drivers”

You can open the “Configure Drivers” configuration menu by either clicking on the “Cable” icon on the RSLinx toolbar as shown below, or by choosing it from the “Communications” menu.
RSLinx-Configure-CommsStep 2) Select the “RS-232 DF1 devices” driver

RSLinx-RS-232-DF1-DevicesStep 3) Click on “Add New,” and then click on “OK”

RSLinx-add-new-driverStep 4) Select the “Comm Port” which is connected to your CompactLogix

RSLinx-DF1-Devices-Select-Com-PortStep 5) Click on “Auto-Configure”

RSLinx-DF1-Devices-Select-Auto-ConfigStep 6) After a few moments if all your cables are connected correctly you should see the below message:

RSLinx-DF1-Devices-Select-Auto-Config-SucessStep 7) Now click on “OK,” and then expand the “AB_DF1-1” network in the “RSWho” window. Here after a few seconds you should now your CompactLogix:

RSLinx-Browse-RSWhoNOTE: Watch me run through the above steps in today’s episode of The Automation Minute!

I hope the above article on how to setup RSLinx to communicate to a CompactLogix was helpful.

If you have any questions or comments, please feel free to share them with us by filling in the “post a comment or question” link below.

Until next time, Peace ✌️ 

Shawn M Tierney
Technology Enthusiast & Content Creator

Have a question? Join my community of automation professionals and take part in the discussion! You'll also find my PLC, HMI, and SCADA courses at TheAutomationSchool.com.

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Shawn Tierney



  1. Can someone help me to get my CompactLogix l35e plc to communicate with my pc, tried to use bootp to retrieve the mac id, to be able to assign an Ip address but, the CPU is not responding or giving out any information at all- just sitting there.

    • Sounds like it already has an IP address – especially if you cycle power to it and nothing shows up in the BootP utility (assuming you have it setup correctly.)

      Personally, I’d just connect through the serial port and change the IP settings via RSLinx (as I show in other posts,) but I have also heard of people using wireshark to sniff out the IP address.



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