Cisco Console to Null Modem Serial Adapter




About: I am very geeky. I love to do hardware stuff like electronics and robotics projects, as well as software (coding and such). I am a full-time net / sys admin, plus I balance being a manger in there somehow....

Currently, I am lugging around my USB to Serial cable (since my laptop does not have a serial port), a Cisco console cable, and a null modem cable (for older switches and other equipment). When I work on older equipment, I have to unplug my Cisco console cable, find my null modem cable, and then plug all of that in.

Wouldn't it be easier if I had an adapter that I could carry around instead of switching cables? Or better yet; maybe I could make a bunch of these cables and keep them plugged into what few older switches we have left.

I know there are probably adapters out there already, but I did not want to purchase anything. I figured making one would be easy enough. Especially since I had about a billion console cables in a box from all the Cisco stuff we ordered (better to reuse than hitting the trash can). So I grabbed the parts and headed to my workbench.

Step 1: Parts and Tools Needed


2 Cisco Console Cables
1 RJ45 Network Jack


Scissors, knife, or cable cutters (or all three... the shielding is tough!)
Needlenose Plyers
Punch down tool (unless you have an RJ45 that does not require a special tool)
(OPTIONAL) Multimeter to test the pinouts

Step 2: Cut the Second Cisco Cable

Get out the scissors and cut the second Cisco cable in half. You can take the end that has the RJ45 jack on it and throw it in a safe place for some other project.

We are going to use the section of cable that still has the 9 pin adapter on it. Take the end of that cable and strip the wiring about half inch down.

Step 3: Wire the RJ45 Jack

Now comes the tricky part. We need to match the wiring in the jack to be configured for RS232 null modem with full handshaking. I found this page very helpful when I was wiring: RS232 serial cables pinout

Some colors might vary on the Cisco cables (I checked the pile we had), but not much. White and gray are the only colors that I noticed changed in my stack of cables. You might want to grab your trusty multimeter and test the cables for your pinout diagram.

See the wiring chart picture for details.

Step 4: Finished!

Once the cables are safely wired into the RJ45 jack, simply connect the first, untouched Cisco Console cable into the jack. TADA! You now have a quick and easy cable that can be used as both a Cisco Console cable or a Null Modem Cable!



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    9 Discussions


    8 years ago on Introduction

    I do not believe in cutting cables. You can simply create Null Modem cable over the network by connecting the sockets you use from the parch panel with a so called "roll-over" Ethernet cable. That is a 1-8 pins go to 8-1. It may be harder to find to buy one than make one at home with a cramping tool. So putting head to head: Cisco Console cable - Ethernet "roll-over" cable - Cisco Console cable you create a Null Modem cable. :) You're Welcome!

    Creepy Kid

    8 years ago on Step 3

    I am uncertain on how to read this chart. Is the Orange on the Cisco cable the RJ-45 equivalent of Blue, because thats immediately to the right, or the RJ-45 equivalent to Orange-White, because they share the same number?

    1 reply
    cowenCreepy Kid

    Reply 8 years ago on Step 3

    Simple you read the chart the way the cable was crimped. Do not mind the color in the cable the position of the color is the important part. Every Jack uses the 568a/b standard the author chose the 568B pin out to use. To actually color code this to a jack would assume that CISCO uses the same colors all the time. This would be a 90% true statement. Looking at the crimp end with the gold pins facing you record the colors and what pin that color goes to should follow the above chart then you need to match that position to the correct position on the CAT5 jack using a 568B configuration as the chart shows above. I build these cables daily you just need to record and know that the jack has to match the end you cut off. The author also put the correct null modem swaps of hand shacking into the cable on the re build. pin 7 never got to pin 1 in a network cable. you just need to not think about 568a/b cable standards here and what does it take to connect and switch handshaking and data flow for RS232.


    9 years ago on Introduction

    BTW, on that table, is that the wiring for the rollover cable, or the wiring for the new nullmodem cable?


    11 years ago on Introduction

    Nice job, done very neatly. What is cisco again? It's a program that lets you chat or something.. right? I forgot. :P

    4 replies

    Reply 11 years ago on Introduction

    Sorry, but my sarcasm detector has never been that great. Just in case people want to know, Cisco is mostly switches and router devices. I recommend using them whenever possible. I have not found a competitor yet that can match Cisco's hardware, software, and support.

    Check them out at

    And no, I do not work for nor do I get paid to endorse Cisco in any way. They just make great stuff and I will always give praise where praise is due.


    Reply 11 years ago on Introduction

    No, I did not mean to accuse anyone. I was just saying that I cannot detect sarcasm. Everything is cool and I appreciate the question. Thanks man!