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DP83822EVM: RMII master clock behaviour

Philip Jönsson
Prodigy 10 points
Part Number: DP83822EVM

Hi

I am using the DP83822EVM together with a STM32H7-DK and has configured DP83822EVM via bootstrapping. Reading the registers over MDIO works and the PHY is configured as RMII master with a clock output on COL pin (pin 29). I am using the HAL driver in the STM32H7-DK for Ethernet communication.

I have not gotten it to work though. When i measure the output clock signal it is not behaving as expected.The clock signal has the correct frequency, 50 MHz, but the signal looks like a sine wave and goes from 1V to 2.4V. The behaviour I am expecting is a square wave that goes from 0V to 3.3V. Should the clock signal look like this?

I have also measured the clock signal on the default pin for clock output, RX_D3, pin 7, but that generates the same strange clock signal.

  • 0
    TI__Expert 3725 points

    Hi Philip,

    Did you modify operation of the PHY by editing registers?

    You can not use pin 29 to read clk_out unless you set it superficially via software.

    By default you should be able to read clk_out on RX_D3(Pin 27, not pin 29/7) as per datasheet.

    Please try the reading again on correct pin and let us know if you still see this. 

    Best,

    Alon

  • 0 in reply to Alon Kopelman
    Prodigy 10 points

    Hi

    I have modified the operation of the phy to use pin 29 (COL) as clk_out. That is done by writing to register 0x0463 IOCTRL2 BIT 2:0 to 011: "clock reference according to bits[6:4]" and BIT 6:4 to 100: "RMII Master mode reference clock: 50MHz ". Is this correct and do I have to write to any other registers toconfigure the clk_out?

    As I also wrote in my original post: I have tested to not change the clk_out pin and use RX_D3, but this is also generating a clock signal like the one on COL pin.

    /Philip

  • 0 in reply to Philip Jönsson
    TI__Expert 3725 points

    Hi Philip, 

    Do you get link-up? Have you tried sending and receiving packets?

    It is likely you are not probing correctly, can you try using a high impedance probe, and to make you are probing correctly using the correct load.

    Best, 

    Alon

  • 0 in reply to Alon Kopelman
    TI__Expert 3725 points

    Hi Philip,

    I will go ahead and close this forum if there are no further questions. 


    Please feel free to reach out again with any query. 

    Best,

    Alon