Understanding the RJ45 ethernet jack

[chitransh92]

I was going through Open Rex design where in I am struggling at RJ45 that the pins, 1,6,7,12 you have connected to ground through 100n cap.
My doubt is 1. what is the significance of the centre tap pin?
2. Does this pin works same for Tx and Rx?
3.what if we pull this pin up to 3.3 or Vdd?



Thanks!

[robertferanec]

This depends on your PHY - if it modulates the output or not. I think, some PHY only generates the signal and you need to add DC on the middle of the transformer. Some PHY automatically generates the signal modulated on DC inside PHY and they do not need DC on the center tap. But I am not expert on PHY, you may want to study it closer.

[chitransh92]

Thanks Robert.