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DP83848: PHYAD[4:1] weak internal pull-down resistors - what size??

Jesper Kristensen1
Prodigy 130 points

Hello.

After having struggling some days with a DP83848 that moves around in the MDIO PHYAD-field after reset of our propietary system, I have finally concluded that the  "PHYAD[4:1] pins weak internal pull-down resistors" are apparently NOT able to force down the four RXD[3:0] lines against the AT91SAM7 uController fast enough, so that '1's are latched upon reset rather than '0's...

Therefore:

 - Where in the documentation, datasheet etc. is i stated what these "internal weak pull-downs" actually constitute in terms of ohms or a current equivalent?

In principle, my question goes for the "internal weak pull-ups" on other signals, as well.

Thanks!

BR - Jesper K, DK.

  • 0
    TI__Mastermind 31600 points
    The internal pulls will typically be in the range of tens of kOhms. These internal pulls are not intended to overdrive a competing device. In other words, the expectation is that the MAC connected to these pins is not driving or pulling them during reset and/or power up.

    It will be necessary to prevent the uController from driving or pulling these pins during initialization. If the uController cannot be controlled during its initialization, then the PHY should be held in reset until the uController has completed initialization and is no longer driving or pulling these pins.

    Patrick
  • 0 in reply to Patrick OFarrell
    Prodigy 130 points
    Hello Patrick.

    Sorry for the late Reply.

    Your answer was in principle exactly what I was looking for. ;-)
    I have another "weak contender" in the other end of some of the lines and no external pull's, so the Reset situation becomes rather unpredictable.

    Thanks!

    BR - Jesper K.