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DP83867IS: Required external termination

user4497266
Intellectual 260 points
Part Number: DP83867IS

The datasheet is a bit vague (unless I have missed something) about needed termination for unused pins.

The datasheet states "NOTE: Internal pullup and pulldown resistors on the IO pins are disabled when the device enters functional mode after power up". But in chapter "6.1 Unused pins" it states "DP83867 has internal pullups or pulldowns on most pins. The data sheet details which pins have internal pullups or pulldowns and which pins require external pull resistors".

So how must I terminate JTAG?

And if I strap it to only use SGMII, do I still need to terminate the unused RGMII input pins?

Regards, Jonas

  • 0
    TI__Mastermind 18425 points
    Hi Jonas,

    JTAG TDI, TMS, and TDO can be pulled high using a pull up resistor (e.g. 4.7Kohm). Unused RGMII input pins can be pulled low using external pull up resistors. These are recommendations and not requirements. The PHY will work without these external pull resistors. This is more of a precaution to avoid any noise from falsely toggling input pins to the PHY. Please not that in SGMII mode, the RGMII output pins will still work as strapping pins to control their respective features. If you decide to put external pull resistors on the strapping pins then please refer to the strapping resistor table for selecting the right value.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Intellectual 260 points
    Hi Aniruddha

    Ok, so the JTAG input pins (I assume you meant JTAG CLK and not TDO) does not have internal termination?
    And the same goes for the RMII input pins.

    I'm well aware of the importance of terminating all inputs, used or not. But integrated circuits tends to have internal pull-up on most pins so that external ones can be omitted. These internal resistors are usually in the range 50-100 kohm and therefore a bit sensitive to noise.
    Is it this you are reffering to when you say "this is more of a precaution to avoid any noise from falsely toggling input pins to the PHY" or are these inputs very high-impedance (in the range megaohms)?

    Regards, Jonas
  • 0 in reply to user4497266
    TI__Mastermind 18425 points
    Hello Jonas,

    Pulling unused pins is a recommendation and not a requirement. The PHY has weak internal pull ups (kohms) and the PHY will still work with unused pins left floating. Pull resistors are indeed precaution against any noise inadvertently toggling a pin.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Intellectual 260 points
    Thank you for clarifying it Aniruddha

    But then I suggest you change the "NOTE: Internal pullup and pulldown resistors on the IO pins are disabled when the device enters functional mode after power up" comment in the datasheet.

    Regards, Jonas