DP83TC814R-Q1: RMII mode TX/RX termination

Hi Kazuki,

Thank you for reaching out. From our understanding DP83TC814 do have a internal pull down resistor on the RX/TX bus in RMII mode. The stability shouldn't be a concern RMII communication. We don't really recommend putting PD resistors on the RX/TX bus. 

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Regards,

Hillman Lin

Hello Hilliman,

Thank you for your swift answer.

You said there is internal PD during RMII mode on TX and RX but datasheet said there isn't any PD as follows.
https://www.ti.com/lit/ds/symlink/dp83tc814r-q1.pdf#page=14

This is just confirmation but is datasheet description typo?

Thank you and best regards,
Kazuki Kuramochi

Hi Kazuki,

Sorry for the confusion. You are correct on there is no internal pull down resistance during RMII mode on TX and RX. However, I believe during the RMII commination, the TX and RX lines will always be pulled up or pulled down which is drive either by PHY or MAC. There shouldn't be any floating condition or stability concern. Am I correct on this statement? Again sorry for the confusion. We usually don't recommend customer use PD on the RX/TX bus.

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Sincerely,

Hillman Lin

Hello Hillman,

I understand that there isn't internal PD but PHY and MAC's TX port driver maintain Low or High status continuously in RMII mode.
So the bus never become unstable condition during RMII mode operation.

Thank you and best regards,
Kazuki Kuramochi