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DP83867IS: Strap configuration

Atsushi Takahashi
Expert 1415 points

Tool/software:

Hi Team,

I have some question about strap config.

<Q1>
GPIO_CTRL is being used in MODE3 with Rhi=6.04kΩ, Rlo=2.49kΩ.
The GPIO_CTRL strap function is Autoneg Disable.
In MODE3, Autoneg Disable=0. Does this indicate Autoneg Disable? Or does it indicate Autoneg Enable?
The customer plans to use it at a fixed speed of 100Mbps with Autoneg disabled.

<Q2>
LED_0 is being used in MODE1 with Rhi=2.49Ω, Rlo=11kΩ.
The LED_0 strap function is SGMII Enable.
In MODE1, SGMII Enable=0. Does this indicate SGMII Enable? Or does it indicate SGMII Disable?
The customer will use it with SGMII.

<Q3>
The datasheet states the following.
Note
RX_D1 is not a strap input, but this pin must be populated with the same strap resistors chosen for RX_D0. RX_D0 and RX_D1 form an SGMII differential pair. The dummy straps on RX_D1 are
required to provide a balanced load for this SGMII differential pair.
The customer is using SGMII_COP/RX_D0 in MODE4 with Rhi=2.49Ω, Rlo=OPEN, and SGMII_CON/RX_D1 in MODE1 with Rhi=OPEN, Rlo=OPEN.
Is this a problem?

Best Regards,

  • 0
    TI__Genius 12441 points

    Hi Atsushi-san, 

    Q1:  

    Atsushi Takahashi said:
    In MODE3, Autoneg Disable=0. Does this indicate Autoneg Disable? Or does it indicate Autoneg Enable?

    This means Autoneg will not be disabled. Thus, Autoneg is enabled. You can think of it as Autoneg /Enable.
    Q2: 

    Atsushi Takahashi said:
    In MODE1, SGMII Enable=0. Does this indicate SGMII Enable? Or does it indicate SGMII Disable?

    This means SGMII is disabled. To enable SGMII, SGMII Enable=1.

    Q3:

    Atsushi Takahashi said:
    The customer is using SGMII_COP/RX_D0 in MODE4 with Rhi=2.49Ω, Rlo=OPEN, and SGMII_CON/RX_D1 in MODE1 with Rhi=OPEN, Rlo=OPEN.

    Yes, this will be a problem as the differential signals will have different impedance. Place ensure that the same strapping on RX_D1 is done to match the impedance on the signal. 

    Best,
    J

  • 0 in reply to J
    Expert 1415 points

    Hi J-san,

    Thank you for your reply.

    They are using SGMII 4-wire and didn't use SGMII_COP/RX_D0 and SGMII_CON/RX_D1.

    In this case, can I think that the strap resistors don't need to be the same?

  • 0 in reply to Atsushi Takahashi
    TI__Genius 12441 points

    Hi Atsushi-san

    We recommend to have the option to put strap resistors to match RX_D0, but you can DNI the strap resistor in the layout since the pins are not used. 

    Best,
    J