I'm planning to use RealTek RTL8211F Ethernet PHY. I have an example schematic.

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The problem here is that the RJ45 Ethernet connector 48F-01GYDXNL is very difficult to get and I'm also missing a 3D-model of it in my Altium CircuitMaker design tool.


The RJ45 Ethernet connector 48F-01GYDXNL is suitable for 1000-BaseT, but I don't need so much speed. I'm happy with 100-BaseT speed. Therefore I could use the simple HanRun HR911105A RJ45 Ethernet connector instead, that are used for 100-BaseT applications.


When I'm looking at the data sheet of the Ethernet PHY device RTL8211F. I wonder what do I need to change if I want to use the HanRun HR911105A connector instead of 48F-01GYDXNL?

By looking at the data sheet of RTL8211F, I can understand that the pins MDIP0, MDIN0, MDIP1, MDIP2 are being used. The rest of the MDI-pins are floating.

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  1. Can I leave MDIP2, MDIN2, MDIP3, MDIN3 floating?
  2. Is it the software that configure if I'm going to use 100-BaseT or is it the LED-pin configurations?

1 Answer 1

  1. They are internally terminated, but leaving them unconnected is not the same as wiring it to a transformer and not using them if the link partner doesn't. You should ask for manufacturer recommendation, plus, if you don't need 1Gbps speed, you can get cheaper PHY ICs without 1Gbps.

  2. LED pin cannot be used to disable 1Gbps operation. You need to configure the chip in software to not advertize 1 Gbps in autonegotiation. Otherwise, they will negotiate that they support 1Gbps and try to use it, but it will be impossible to form a 1Gbps link. They might never switch to 100Mbps.

Also, I assume you talk about 100Base-TX, as there is no such thing as 100Base-T.

It might be easier to just get another 1Gbps MagJack and get the full benefit from that chip than to think how to adapt this to 100Mbps only design.

  • \$\begingroup\$ Yes. But I cannot find 1 Gbps MagJack at JLCPCB. I don't know were I should look. jlcpcb.com/parts/2nd/Connectors/… \$\endgroup\$
    – euraad
    Commented Apr 5 at 8:31
  • \$\begingroup\$ @euraad You can always put separate 1 Gbps transformer and any connector without magnetics. \$\endgroup\$
    – Justme
    Commented Apr 5 at 13:08
  • \$\begingroup\$ I found a 1000Base-TX connector from JLCPCB. It's Pulse J0G-0001NL \$\endgroup\$
    – euraad
    Commented Apr 6 at 11:58

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