Forums

Ethernet magnetics polarity?

Started by Unknown March 8, 2008
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:
  http://www.freeimagehosting.net/uploads/1b29a64249.jpg

<sky465nm@trline5.org> wrote in message news:fqtcpv$c88$1@aioe.org...
> 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: > http://www.freeimagehosting.net/uploads/1b29a64249.jpg >
No, it doesn't matter, not if you reverse both TD and MX pairs as you have.
On Sat, 8 Mar 2008 10:18:21 -0000, "Andrew Holme" <ah@nospam.co.uk>
wrote:

> ><sky465nm@trline5.org> wrote in message news:fqtcpv$c88$1@aioe.org... >> 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: >> http://www.freeimagehosting.net/uploads/1b29a64249.jpg >> > >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.