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Thread: Need RJ-45 pinout help

  1. #1
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    Need RJ-45 pinout help

    I'm a fairly new at PCB design and I'm building a board for a Teensy 4.1 and am going to add an RJ-45 port on board. I'm looking to use the below part. I need to match the Teensy pins to the schematic\footprint pins. I'm sure this is an easy question, but so far "RJ-45 pinout" doesn't seem to turn up the right stuff and I need to know what order to connect the Teensy pins and how to connect the LED and shield pins.

    Part:
    https://www.snapeda.com/parts/2-4065...h&welcome=home

  2. #2
    Senior Member+ defragster's Avatar
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    Is this to mate to a T_4.1? Look at PJRC.COM for their adapter - and has link IIRC to OSHPARK where there is a drawing of the PCB - between those two the parts and wiring to the proper indicated MagJack should be discoverable.

  3. #3
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    Thanks. I wanted documentation rather than risk messing it up when I eyeball it.
    I'm still not sure how to configure the rest of the pins...and can't confirm if the footprint of the jack is the same, so there is some risk looking at an existing part.

    I found this:
    https://networkel.com/rj45-pinout-diagram/
    ...it doesn't tell me how to configure the rest of the pins of the jack though.

  4. #4
    Senior Member+ defragster's Avatar
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    This page : pjrc.com/store/ethernet_kit.html

    It has this image:
    Click image for larger version. 

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    Using the specified MagJack - all the stuff in the box handles bringing the needed signals to the numbered pins to route to the indicated components as supplied in that kit.

  5. #5
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    Thanks. I guess, I'm fuzzy on what a MagJack is\does as opposed to other ports. I have a footprint and schematic part for that MagJack part...JLCPCB doesn't stock it though darn Thanks for the help!

  6. #6
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    Actually, JLCPCB has a number of MagJacks that can be made to work with the Teensy 4.1. But before that, a PSA.

    A MagJack is an RJ45 connector with the necessary magnetics to connect an Ethernet Phy to an Ethernet Network. Each one is different - there is no pinout standardization. So, you need to wire each one differently. It is not not hard to do once you understand how they connect. The T4.1 has a 100MHz Ethernet Phy built in so connecting to an Ethernet Network is pretty easy.

    So back to the JLCPCB MagJacks. I tested several of the 100 MHz parts they carry. Here is the schematic of my test board.
    Click image for larger version. 

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    There is some discussion of whether the 1 uF caps are really necessary but the Ethernet Phy Data sheet has them so I do too. The box with RP, RN, LED, G, TP and TN is the 2x3 2mm header. If you are going to run the T and R traces longer than 25mm to the MagJack, you should use differential routing. Most EDA tools have that.

    The 3 I tested are:
    HR911103A (0 in stock right now)
    HR911105A
    RB1-2D6B8K1A

    Also, if you have spare pins on the Teensy, you might want to use the second LED to indicate something (waiting for connection or?)

    [edit] I had the wrong schematic, the one in-line is correct.
    Last edited by PhilB; 04-09-2021 at 08:32 PM.

  7. #7
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    Thanks! I've also been hamstrung by trying to match available parts on JLCPCB and what I can get schematic and footprints for on SnapEDA. I lucked out on HR911105A above. Double thanks!

  8. #8
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    If you get a board built by JLCPCB, please write back with a status report. I just populated the MagJacks myself. I'd like to know how them assembling it goes for you.

  9. #9
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    RJ45 Pinout for a LAN Cable
    Pin 1 → White and Green (Transmit +) wire
    Pin 2 → Green (Transmit -) wire
    Pin 3 → White and Orange (Receive +) wire
    Pin 4 → Blue wire
    Pin 5 → White and Blue wire
    Pin 6 → Orange (Receive -) wire
    Pin 7 → White and Brown wire
    Pin 8 → Brown wire

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