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Original question:

DP83TG720S-Q1: DP83TG720S polarity

DP83TG720S-Q1: DP83TG720S SGMII P N flip

chenglei yang
Prodigy 150 points
Part Number: DP83TG720S-Q1

Tool/software:

Hi，

We connectted  DP83TG720S to a switch using SGMII.  But we connect RX_P of  DP83TG720S  to RX_N of switch,  RX_N of  DP83TG720S  to RX_P of switch.

  

How to change the SGMII  P and N?   I have set SGMII_CTRL_1 Register (Offset = 608h)  bit 7 and bit8 to 1,  But SGMII still can not link.

Can you help?

Thanks a lot.

  • 0
    Prodigy 150 points

    What's more, if this DP83TG720S need initial reg sequence table?  I had not set any register except SGMII_CTRL_1 Register (Offset = 608h).

  • 0 in reply to chenglei yang
    TI__Genius 13245 points

    Hi Chenglei,

    chenglei yang said:
    What's more, if this DP83TG720S need initial reg sequence table?  I had not set any register except SGMII_CTRL_1 Register (Offset = 608h).

    The intialization script is here: https://www.ti.com/lit/an/snla371b/snla371b.pdf?ts=1724961229133 

    This initalization script is required to meet Open Alliance specifications.

    chenglei yang said:

    We connectted  DP83TG720S to a switch using SGMII.  But we connect RX_P of  DP83TG720S  to RX_N of switch,  RX_N of  DP83TG720S  to RX_P of switch.

      

    How to change the SGMII  P and N?   I have set SGMII_CTRL_1 Register (Offset = 608h)  bit 7 and bit8 to 1,  But SGMII still can not link.

    Can you help?

    Thanks a lot.

    Can you try

    1. Resetting the PHY by writing 0x1F=0x4000 after inverting polarity

    2. If resetting the PHY does not work, you can disable SGMII autonegotiation in both SGMII Switch and 720S

    Best regards,

    Melissa

  • 0 in reply to Melissa Chang
    Prodigy 150 points

    First, I had set the following table to DP83G720S,   DP83G720S did not link.

    Second,  I restarted the PHY by writing 0x1F=0x4000 after inverting polarity, DP83G720S did not link.

    Finally,  I disabled SGMII autonegotiation in both SGMII Switch and 720S, DP83G720S still did not link.

  • 0 in reply to chenglei yang
    TI__Genius 13245 points

    Hi,

    Are you able to try using normal the polarity to see if the 720 works normally? I want to confirm the PHY is functioning normally.

    1. One other way to confirm would be to connect a link partner to the MDI pins (TRD_P and TRD_M  pins) and check linkup in register 0x1.

    Note that link up can only occur if one device is set to master and one device is set to slave.

    2. The other way to check for functionality is to read registers 0x0-0x1F.

    Best regards,

    Melissa

  • 0 in reply to Melissa Chang
    Prodigy 150 points

    After change some config on switch:

    When I disable SGMII autonegotiation on 720 and enable autonegotiation on switch,  both 720 and switch can link up.

    On 720 side, reg0x060a = 0x926

    Why must I stop the autonegotiation of 720?  

  • 0 in reply to chenglei yang
    TI__Genius 13245 points

    Hi,

    I'm not sure, we would have to do further testing. It could be the SGMII autoneg settings of the Switch and PHY are not matching.

    However, there are no concerns with disabling SGMII autoneg on both sides, as long as you are not seeing packet errors, this is a valid configuration. 

    Best regards,

    Melissa