I am doing Ethernet communication to/from an MCU.

I got it working great with an ENC28J60 development module: https://www.digikey.com/product-detail/en/olimex-ltd/ENC28J60-H/1188-1044-ND/3471433

I recreated the module layout w/ DIP components on breadboard. It works pretty good though not as reliable, the obvious reason being that im using a birds nest of wires vs a module.

Now I am going recreate this interface circuit on a PCB. Are they any trace width/ length recommendation I should use?

I found this: http://ftp1.digi.com/support/documentation/022-0137_F.pdf

It says I should the keep the trace impedance below 50ohm for signal traces... But since Ethernet operates at different frequencies do i need to know ahead of time what frequency I'm transmitting at?

Should the Tx/Rx pairs be routed side by side or above/below on different sides of the PCB.

I am going to be using basic 1oz Copper, 2 layer board. I probably wont be able to keep the traces all on one side... Meaning the ground plane wont be flawless. How big of deal in this? I mean I did get it working on breadboard w/ jumper wire.

Thanks Tony

  • \$\begingroup\$ Are you laying out a board and using the module as a component on the board or laying out for the chip itself? \$\endgroup\$ – Dean Franks Nov 16 '17 at 16:55
  • \$\begingroup\$ With 2 layers, getting the impedance right is going to be tricky, because the traces would be very wide. \$\endgroup\$ – Simon Richter Nov 16 '17 at 16:59
  • \$\begingroup\$ Laying out the chip itself... Also, I will be using an RJ45 with the magnetics built into it so that should make it easier. \$\endgroup\$ – Tony Nov 16 '17 at 17:06
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    \$\begingroup\$ Because you are only running at 10Mbps you will get away with 2 layer boards if you are reasonably careful about layout. Place the ENC28J60 close to the magjack and route the TX/RX pairs first, keep them on one side and route as a differential pair without vias and at least 50 mils clear of other traces if possible. Try to have a continuous ground plane under these traces. Controlling the impedance on the differential pairs is not critical, but try to keep the lengths on the two traces for each signal pair closely matched. \$\endgroup\$ – Dean Franks Nov 16 '17 at 17:35
  • \$\begingroup\$ Thanks! Also I see there are different typologies for the magnetics... Shown in this datasheet: productfinder.pulseeng.com/products/datasheets/J402.pdf. The Ethernet module I used has type 'J1012'. Unfortunately this is hardest type to find... I want to have options for the connector orientation and mounting type; I can't find any other connector with the same circuit. How critical is this transformer setup? Could I use the 'J1011' type instead? \$\endgroup\$ – Tony Nov 17 '17 at 13:14

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