I'm autumn and recently working on a project that wants to connect two IC with part: ENC28J60 (that connects microcontrollers (with SPI interface) to Ethernet and LAN Networks) directly in a PCB board (witouth cables and only with cupper tracks in my PCB.

As you know for connecting ENC28J60 (or any 10mbps LAN device) we need a 1:1 filter (it used for CMRR increasing) and you can find lots of schematic for that in google.

for the Ethernet cable (4 twisted pairs cable) we connect the TPIN+, TPIN-, TPOUT+ , TPOUT- pins of ENC28J60 to 10 Base-T Filter and then Connect Ethernet Cable to otherside of the filter. it's common and simple.

But the Question is: How can i connect two 10Base Ethernet Device (Like ENC28J60) without filters in short distance? (like a small PCB) (short distance will not cause noise and we don't need any filter for CMRR and twisted pairs).


Best Regards.

  • \$\begingroup\$ Why not use RS-485 instead? Or just a direct UART connection? \$\endgroup\$ Commented Apr 17, 2014 at 3:06
  • 3
    \$\begingroup\$ Why go through the effort of full blown ethernet OSI layers 0 (copper traces, unofficial layer), 1 (PHY, 10Base) and 2 (LLC, MAC), probably 3 (IP) and 4 (TCP) if you just want to connect two devices on a PCB? Each layer listed is an extra abstraction in hard or software and costs resources/money. Why not directly interconnect the SPI interfaces? \$\endgroup\$
    – jippie
    Commented Apr 17, 2014 at 7:04
  • \$\begingroup\$ You should only need to go ethernet if your on a network to provide isolation etc... direct connect has the advantages of being faster and cheaper ... unless there is a good reason I would put wire links across your component parts in production and get a slap on the back for reducing inventory, complexity, increasing relability and cutting costs .... nice bounus! \$\endgroup\$
    – Spoon
    Commented Apr 17, 2014 at 12:37

2 Answers 2


Try this application note from Micrel. It's their app note, so they promote their devices that they've tested it with, but I'd be very surprised if it doesn't work on pretty much any Ethernet PHY - they're all interoperable.

edit: The app note tells you exactly how to wire two PHY's back to back, including if one or both of them are "current mode", or "designed to interface to a transformer".


It isn't easy to connect two devices without at least a transformer, since the output stage of the ENC28J60 (and pretty much any other 10base-T device) is designed specifically to drive a transformer. Furthermore, the input stage is designed specifically to receive a signal that has been coupled through a transformer as well.

  • \$\begingroup\$ Can you get away with both sides using the same transformer? \$\endgroup\$ Commented Apr 17, 2014 at 6:01
  • \$\begingroup\$ This is probably not true. For example, you can probably make the driver happy with a network of resistors, and then capacitively couple to the receiver. \$\endgroup\$ Commented Apr 17, 2014 at 15:14

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