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DP83848 SNI mode

Tyrel Newton
Prodigy 50 points

Regarding the SNI MAC interface mode for the DP83848, its unclear what (if any) the oscillator/crystal requirements are. Does an external cyrstal/oscillator even need to be connected to X1/X2 for SNI mode? And if so, what does the frequency need to be? 10 MHz? Or is TX_CLK supposed to be an input in SNI mode and driven by the MAC? A reference implementation or some feedback would be very helpful.

Thanks,

Tyrel

  • 0
    TI__Mastermind 31600 points

    Tyrel,

    An oscillator or crystal is required for operation in SNI mode.  The X1 input provides the main reference clock.  Without a clock source for that pin, the DP83848 will not function.

    For SNI mode, the X1 input should use a 25MHz crystal or oscillator.  The specifications for the crystal or oscillator are in the Design Guidelines section of the datasheet.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 50 points

    Patrick--Thanks for the answer, this was the confirmation I needed.

    The problem I had is that in the Design Guidelines, it says "Specifications for CMOS oscillators: 25 MHz in MII Mode and 50 MHz in RMII Mode are listed in Table 7 and Table 8." As far as I could tell, its up to the user to make the leap that the 25 MHz MII specifications are also the 25 MHz SNI specifications (and that the SNI interface also requires a 25 MHz clock).