Missing resistors at Ethernet interface?

[HMüll.4]

Hi,

in schematic of the STM32MP257-DK-board, I found the following resistors at the Ethernet interface being marked with "DNF":

When looking at the board, these resistors are missing (which should be "DNP" in this case?).

From my understanding of the wiring of the Ethernet interface, they should be there, but as one can see, the ETH-port on that DK-board is working properly also without them.

So my question: what is the story behind these resistors which should be there and are missing while everything is working properly? Is there some other hack which makes these resistors obsolete/which replaces these resistors?

Thanks!

 

[PatrickF]

HI @HMüll.4 

 

as you can see in the MB1605 Bill of materials, those 'DNF' resistor are 'No Fitted'.

They are also shaded on purpose inside the schematics.

Please refer to Realtek RTL8211F documentation, the resistors are here to control various default settings of the PHY (delays, MDIO address, etc...) using either pull-up or pull-down sampled by the PHY during its start up. Default settings as in the board BOM are strongly recommended to be kept unless you are experienced user mastering the PHY HW and want to trial some different settings or hacks default behavior.

 

Regards.