This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AM335X RMII1_REF_CLK clock output to be used as RMII PHY clock input (50MHZ)

Other Parts Discussed in Thread: TLK110

We want to use AM335X's RMII1_REF_CLK pin output as a clock source for  RMII PHY clock input (50MHZ). We are using TLK110PTR RMII phy with Am335X processor. Please let me know if this connection is ok.

  • Hi,

    This should be possible. Refer to BeagleBone Black schematics, you can see that there is the possibility to connect AM335x's MII1_REF_CLK to LAN8710A's XTAL1/CLKIN by populating R140.

    Best Regards,
    Yordan
  • Hi Manoj,

    Disregard my answer.

    See the recommendations from AM335x TRM:
    Table 14-1. Unsupported CPGMAC Features:

    RMII reference clock output mode : RMII reference clock does not satisfy input requirements of RMII Ethernet PHYs.

    Use external crystal, as suggested in all reference boards: AM335x EVM SK & BeagleBone Black

    Best Regards,
    Yordan
  • Hi,
    Thanks for information. I have further query. I ma using TLK110PTR RMII PHY and will external oscillator as clock source and use clkout of RMII PHY as reference clock to AM335X RMII1_REF_CLK clock input for synchronization. Please let us know if this is valid connection to work with AM335X and TLK110PRT clock source input.
  • No.

    The external oscillator output should be connected to both the TLK110 and the AM335x. The TLK110 CLKOUT pin is only a 50MHz reference output clock. If you look at the TLK110 RMII timing diagrams you will see the RMII signals are timed to the XI pin, not CLKOUT.

    Also read Advisory 1.0.16 of the AM335x Silicon Errata.

    Regards,
    Paul
  • Use of the RMII reference clock output is not supported. Please refer to Advisory 1.0.16 in the device silicon errata (SPRZ360G) for details.