Ethernet magnetics polarity?

Mar 08, 2008 2 Replies

When using a gigabit ethernet PHY. Does it matter if one wires the magnetics with the "wrong" polarity like below ..? (reason being pcb routing, and the ethernet transformer isn't straightforward)



From this: To this:



RJ45 pin1 --- MX1+ ** TD1+ --- MDIA_P RJ45 pin1 --- MX1- ** TD1- --- MDIA_P RJ45 pin2 --- MX1- ** TD1- --- MDIA_N RJ45 pin2 --- MX1+ ** TD1+ --- MDIA_N



RJ45 pin3 --- MX2+ ** TD2+ --- MDIB_P RJ45 pin3 --- MX2- ** TD2- --- MDIB_P RJ45 pin6 --- MX2- ** TD2- --- MDIB_N RJ45 pin6 --- MX2+ ** TD2+ --- MDIB_N



RJ45 pin4 --- MX3+ ** TD3+ --- MDIC_P RJ45 pin4 --- MX3- ** TD3- --- MDIC_P RJ45 pin5 --- MX3- ** TD3- --- MDIC_N RJ45 pin5 --- MX3+ ** TD3+ --- MDIC_N



RJ45 pin7 --- MX4+ ** TD4+ --- MDID_P RJ45 pin7 --- MX4- ** TD4- --- MDID_P RJ45 pin8 --- MX4- ** TD4- --- MDID_N RJ45 pin8 --- MX4+ ** TD4+ --- MDID_N


Magnetics schematic:

formatting link



No, it doesn't matter, not if you reverse both TD and MX pairs as you have.

This is part of the reason auto MDI and auto MDIX have become common in routers and switches.

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