STM32H743BIT6: same clock source for both MCU and ethernet PHY?

[Meghna]

Hello, I am using STM32H743BIT6 as a MAC for DP83TC814R Ethernet PHY, I have one query regarding oscillator, I am using Ethernet in RMII slave mode which requires 50MHz reference clock, can i use the same clock which i am using for MCU HSE or should i use different one for EThernet PHY, But how the clocks can be synchronised in that case?

[MHoll.2]

Please read my previous answer!

- OSC_IN on the STM32H743BI is on Pin 32 (not Pin 33!)

- You need to connect the RMII_REF_CLK  input (Pin 44) to the same clock as XI of the DP83TC814

[Meghna]

Corrected, but we are using ETH in RMII slave mode then in that case PA1(44) can be left open right?

[MHoll.2]

NO, the RMII Block in the STM32 need the RMII_REF_CLK!

[Meghna]

Is this correct?

[MHoll.2]

YES!

For EMC reasons, i would put a 3. resistor from OSC50M to PA1, but this dipends a lot on the PCB Layout (Track impedace an length).

like this:

OSC50M -> resistor -> PH0_OSC_IN

OSC50M -> resistor -> PA1

OSC50M-> resistor -> XI