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Original question:

DP83822IF: Series termination on signal lines

DP83822IF: IOCTRL register (0x0461)

Dean Hofstetter
Expert 2585 points
Part Number: DP83822IF

Tool/software:

It isn't clear which external pins benefit from setting the series termination resistance.  All the RX pins (RX_D0 to RX_D3, RX_CLK, RX_CTRL)      ..or..     only the RX_D0 to RX_D3 pins?

Whichever pins this register controls, since the default is 58.07 ohms, I assume putting additional series termination resistors on these lines is a bad idea.  We currently have 33 ohm external resistors on all the RX pins, and I'm thinking of making them 0 ohm.

Thanks, Dean

  • 0
    TI__Mastermind 24998 points

    Hi Dean,

    I am confirming if this register controls all MAC pins or only data pins - please expect feedback early next week.

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    TI__Mastermind 24998 points

    Hi Dean,

    All MAC interface pins are affected by impedance control register.

    For first revision of design, 0ohm placeholder resistors are recommended to further adjust series resistance if needed.

    Thank you,

    Evan

  • 0 in reply to Evan Mayhew
    Expert 2585 points

    I should have specified that that I'm using the DP83822 in RGMII mode.  Therefore, from the PHY point of view, it drives the following lines:  RXD0 to RXD3, RX_CLK, and RX_CTRL.  Six lines in total.  Series termination only works if you place the resistors next to the driver.  I would expect this register to only control those pins.

    It doesn't make sense for the DP83822 to have series termination resistors on the TX lines, as those are all inputs in RGMII mode.  Please double check your answer.  If ALL the MAC pins have these resistors, please explain why they are on the TX lines.  Perhaps the RX resistors are series termination, and the TX resistors are parallel termination?  That would make sense.

    Thanks, Dean

  • +1 in reply to Dean Hofstetter
    TI__Mastermind 24998 points

    Hi Dean,

    Sorry for the confusion, the MAC impedance control register only affects the MAC output pins (RX_D/CLK/CTRL/...) .

    Placeholder 0ohm resistors on the TX pins are still recommended for the option to adjust impedance matching if needed.

    Thank you,

    Evan