I have a switch that has a 4 wire (2 twisted pairs) ethernet interface which I want to connect to an i.MX8 Plus MPU (GBit ethernet with 4 pairs). I need to design the PCB that connects the MPU to the connector.

  1. Can I just route the two pairs needed to a 4 pin connector (like on the switch)?
  2. Do I need to terminate/disable the two unused ethernet pairs or can I just not connect them?

Thank you for your help.

For Reference: Switch: Botblox rugged ethernet switch MPU: i.mx8 plus


2 Answers 2


You can just connect the two pairs and leave the other two pairs unterminated. You will get a 10 or 100Mbps connection.


You are trying to connect a gigabit ethernet to a 10M/100M switch.

This is normal.

You will have to use the wires that are normally used for 10M/100M anyway.

  • \$\begingroup\$ The SwitchBlox Rugged datasheet says it supports Automatic MDI-X crossover. Is there any benefit in the connection from the i.MX8 Plus MPU to switch being wired as straight though .vs. crossover for the two pairs? \$\endgroup\$ Oct 1 at 18:52
  • 1
    \$\begingroup\$ @ChesterGillon Nothing significant, no. \$\endgroup\$
    – Sneftel
    Oct 2 at 8:52
  • \$\begingroup\$ @Sneftel "Nothing significant" implies there is some difference. Can you elaborate further if you know what it is? \$\endgroup\$
    – jayded-bee
    Oct 3 at 4:59
  • 2
    \$\begingroup\$ @jayded-bee In general for Ethernet, it should not make any difference, except devices supporting MDI-X need to try negotiating the link up by transmitting and receiving on both TX and RX pairs to see if there is another device or not. If the other device is not MDI-X then it is statistically faster by few milliseconds to get link up if you know you don't need to automatically probe both ways. Also there might be bugs in these chips that affect how it works or if you need to disable auto MDI-X or forcibly set which pair is TX or RX, it can be simpler to wire them like they should be wired. \$\endgroup\$
    – Justme
    Oct 3 at 5:50

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