STM32H735 RMII_REF_CLK 50MHz

[PUN CHEE HUEY]

Hi All,

I have a 50MHz clock with 1Vpp and the MAC is not working. The only information I have from the RM and datasheet is this is a digital input pin and never mentioned about the voltage level. Please help what is the clock pulse VPP for RMII reference clock pin ?

Thank you in advance.

[TDK · Accepted solution]

This is a digital input, so it will need to respect the digital input levels. Generally, a low of 0.3 VDD or less and a high of 0.7 VDD or more. It's unlikely a 1 Vpp signal will satisfy both of these.

[LCE]

Custom board or something from ST?

What is the source of the clock? Some PHY like LAN8742?

Check series resistors and for any shorts, also check your GPIO configuration for that pin.

As TDK said, RMII clock level should have the typical 0 .. VDD level.

[PUN CHEE HUEY]

The clock is 1Vpp because ADIN1100 needs 1Vpp for best performance. But I can use the clock source, which is 2.5Vpp to input the STM32 MCU RMII clock reference pin. some rework need to do check.

[LCE]

I don't know the ADIN1100, but for ethernet PHYs the 1Vpp signal usually refers to the ethernet signals coming from / going to the ethernet transformer.

The PHYs RMII interface usually works with its VDD level, or maybe it has some extra supply for the IOs?

[PUN CHEE HUEY]

after put in the clock source with 2.5Vpp, then STM32H735 MAC is workable now.  The phy ADIN1100(analog device) is also ok but with clock source 1Vpp.