Specific Ethernet wiring....

20 Oct 2010

I'm trying to connect my mbed to the network trough a RJ45 connector, but it seems not to see any packet...The only connection that I set up are with the four receive/trasmit as specified in the mbed's cookbook page. Are there any connections that may be required?Any ground connections for example?

21 Oct 2010 . Edited: 04 Nov 2010



The most simple physical connections you need are:

The 4 wires RD+ , RD-, TD+ and TD- to your Router or Ethernet Switch and Power and Ground supplied by the USB download cable to your Computer.

Rolf Meyer posted some thing very helpful :


Jeff Brown supplied a great diagram for MBED to a RJ45 jack with magnetics:


* Yes you need 3.3v and ground to power up the magnetics in any mag-jack (MagicJack, Tyco, Pulse....)


I was having Ethernet communication problems when first got started with MBED....struggled!

I needed a "TEST SYSTEM" to see why I did not connect to the network and pass packets.

So I posted below Ethernet 101 and the steps I went thru. If this is way too simple...it is because I needed simple!

Hope this helps other MBED Users getting started with their first Ethernet connection and projects.

My problem was not the "Physical Ethernet connection" or "Ethernet Software loaded on MBED" it was knowing the correct IP address of MBED. This may be your issue.

If so skip to "F" below....this will save the life of a perfectly good CAT5 cable.

MBED and Ethernet 101 - Physical Connection, Test Software and MBED IP Address.

Most simple TEST to know if you are passing Ethernet packets. (Need Breadboard for MBED, 2-4 foot CAT5 cable, access to DHCP clients on your Router, TEST CODE I will post, USB Load cable for program upload and MBED power supply)

A. Take a good CAT5 cable and cut it in half (about 2' of cable with a RJ45 Plug on one end.)

B. Strip off about 1-2" of the cable plastic cover.

C. Find the following 4 wires: SOLID GREEN , GREEN/WHITE, SOLID ORANGE, ORANGE/WHITE. (cut the other 4 wires to get them out of your way)

D. Strip away the insolation for connection into breadboard (about 1/4") on all 4 of the above GREEN and ORANGE pairs. See picture above MBED "PE"

E. Hook up to MBED (See MBED card or printed on the right side of MBED - Pin label is ABOVE THE PINS):

------------------------------------------GREEN -------------RD + PIN on MBED ------

(To RJ45 Plug)---------------------- GREEN/WHITE---- RD - PIN on MBED ------(To MBED RD +/- and TD+/- Pins)

----------------------------------------- ORANGE-------------TD + PIN on MBED-----

------------------------------------------ORANGE/WHITE---TD - PIN on MBED ----

F. Plug the RJ45 Plug into your Router. Plug your USB download cable into MBED and your Computer.

G. Load EthernetTesterGood.bin program on MBED (or your program you are testing) - Download the code "left of picture above" (same code as posted in public library - Not my program but reposted it).  PRESS RESET ON MBED.

H. Log in to your Router Setup to view all the DHCP clients physically connected to your Router. See picture above.  Test code running on MBED will show up in your DHCP log as my-mbed

If you run your own test code you may not see "my-mbed" in the DHCP log but you can identify the MBED by the MAC address.  If you see your MAC address then the physical connection and software is working!

I. With the correct IP address of your MBED (identified by your Router) type into your browser address: (your MBED address may/will be different than the one I listed here)

J. If your MBED Ethernet connection is working correctly you should see on the Web page:



If you can see this page, your mbed is working properly.

mbed Configuration

mbed RTC time:Thu Jan 1 00:00:00 1970 
mbed HW address: 00:02:f7:f0:10:47

mbed IP Address:


You should be able to load your own Ethernet code on MBED and should work fine!

If you need help with a "non magnetics RJ45 Jack" see link at top of this page or I can post Jack 101 additional help. Pictured above MBED "JM"

Good luck...hope this helps you.

Jeff Mourich

PS: I would have paid $20.00 more if NXP would have put in the box an Ethernet Jack / Board with the 4 pins to wire up to MBED - the break out board I built to hooked up to MBED "JM" above -

Then Ethernet would have been a "GREAT Out of Box Experience" for me.

Spent over 2 hrs and $6.00 anyway on a FRE/Pulse jack - the board and pins I had.....

But I learn when I struggle......I hope this helps others - Other MBED users have helped me...passing it on.

MBED and the MBED Community Users ROCK!

My first BIG Ethernet Project:

Solar charging system - MBED monitor and post to Pachube

22 Oct 2010

I took a RJ-45 connector, superglued two 4 pin headers to it, one on each side, and wired the headers to the pins. Then I potted it in hot glue to protect the connections.

I forgot where I read it (some datasheet or something) that there should be 33nF capacitors in series with each of the data lines. I used 100nF and it works just fine. Ground the other pins to reduce noise. (For PoE, connect the positive Ethernet pins to the input of your voltage regulator.)

22 Oct 2010

Thank you!Now my ethernet connection works fine :)

22 Feb 2011

Thanks man, after fumbling around it worked like a charm with DHCP.

20 May 2011

This is really helpful..Thanks a ton!

24 Aug 2011

for me the cable was different (Norme EIA/TIA568A) : http://www-gtr.iutv.univ-paris13.fr/Cours/Mat/ARS3/DocsTP2/cablage_rj45_LC.pdf





it is a good idea to use a cable (easy to obtain) than a magjack or... thanks

23 Dec 2011

Merry Christmas to all my MBED friends. :) Jeff Mourich www.pbase.com/jeffm

10 May 2013

Hi, I imported the program but could not compile it. Why? By the way, where can I find ethernettestergood.bin for test?

28 Sep 2013

Thanks, it works as I expected.. Cheers!