Query regarding series termination resistor for the RGMII interface of the STM32MP157FAC1

[PS_115]

Hello,

We are designing a custom board using the STM32MP157FAC1 device and interfacing its RGMII interface with the DP83869HMRGZT Ethernet PHY.

We have some queries regarding the PCB implementation of the RGMII interface.

Is it recommended to use series termination resistors on the RGMII signals? If yes, kindly clarify the following:

(1.) Should the series termination resistors be placed only on the TX signals driven by the STM32MP157FAC1?

(2.) Are series termination resistors also recommended on the TX signals driven by the DP83869HMRGZT (i.e., the RX signals of the STM32MP157FAC1)?

(3.) Kindly advise the recommended resistor values and the preferred placement of these resistors with respect to the driver device.

Your guidance on the recommended implementation would be highly appreciated.

Regards,

Prashant 

[mƎALLEm]

That thread should be posted in STM32 MPUs Products and hardware related forum board not in STM32 MCUs Products.

I moved it..

[PatrickF]

Hi ​@PS_115 

 

Please look into AN5031.

Usually, series resistors to enhance signal integrity for unterminated lines must be placed as close as possible of the line driver side.

22 ohms is usually a good value, but might be tailored (or even omitted) by your HW experts upon signal integrity simulations or tests as this depend on PCB stack-up, line length and other parameters.

 

Regards.