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DP83848Q-Q1: clock requirements for RMII mode

Sherry Liang
Genius 10255 points
Part Number: DP83848Q-Q1

Dear team,

In an application note--AN-1469 PHYTER Design & Layout Guide, there is a description about clock requirements as below.

Could you please help analyze why MII mode and RMII master mode can use 25MHz crystal while standard RMII mode can't?

Thanks & Best Regards,

Sherry

  • 0
    TI__Mastermind 40225 points

    Hello Sherry,

    I would like to point out the DP83826 datasheet for more clarification regarding the difference. Standard RMII (shown on pg. 30 as slave/slave) is different from RMII master mode (master/slave). You can see that in RMII master mode, a 25MHz clock signal is used, while in slave mode, a 50MHz signal is used and shared between the master and slave. In a slave to slave configuration, you see the 50MHz signal that is shared between the two devices. These are different standards, and some PHYs support one, the other, or both. The way to tell what the PHY supports is by checking the XI/XO requirements.

    Sincerely,

    Gerome