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Original question:

DP83TG720R-Q1: Schematics of DP83TG720R-Q1

DP83TG720R-Q1: MAC address and RGMII mode selection, pull-up resistor

Francis Pan
Prodigy 10 points
Part Number: DP83TG720R-Q1

Hello, we would like to ask three questions:

1. We use the RGMII mode, but because of the layout problem, the two pull-up resistors given in the specification and the tool cannot be placed. I wonder if there is a way to remove the two pull-up resistors and then use the RGMII mode? That is, all are designed using Mode1 in Figure 2;

2. Figure 2, I would like to ask if we want to use the RGMII mode. What is the difference between these four? How should we choose?

3. Could you please explain the specific difference between Mode1, 2, 3, and 4? And the difference between the four different modes of RGMII? We want to know about the analysis according to the project needs; 

That's all

Thanks

  • 0
    TI__Mastermind 24135 points

    Hi Francis,

    1. We recommend using the strap registers to select RGMII mode correctly. Without the strap register, there maybe some conflict with the MAC side after the power up. We can program the RGMII mode by using following sequence.

    • Step 1: Write 0x608[9] = 0
    • Step 2: Write 0x600[3] = 1 to enable the RGMII
    • Step 3: Check 0x602 for clock delay for RGMII

    2. I am not sure if I understand your question correctly, are you asking for what is the different between RGMII (Align mode), RGMII (TX Internal Delay), and etc...
    If I understand correctly, These four mode are controlling the delay of the clock. It should be according to the following table:

    If MAC’s Configuration is :

    Required PHY’s configuration

    Rgmii Align Mode on TX side

    Rgmii Shift Mode on TX side

    Rgmii Align Mode on RX side

    Rgmii Shift Mode on RX side

    Rgmii Shift Mode on TX side

    Rgmii Align Mode on TX side

    Rgmii Shift Mode on RX side

    Rgmii Align Mode on RX side

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 10 points

    Hi Hillman,

    Thanks very much for your reply and it really help us a lot.But I still have a point need to confirm with you about question 1.

    You recommended that we used register to config the RGMII mode ——My understanding is that we only need to use Code to configure, and we don't need to use hardware resistors. Is this understanding correct?

  • 0 in reply to Francis Pan
    TI__Mastermind 24135 points

    Hi Francis,

    Sorry for the confusion, we recommended using the strap to configure RGMII mode. If you are not able to do so, you can use the following register to enable RGMII.

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 10 points

    HI Hillman，

    I'm sorry that my statement may have caused a misunderstanding, let me explain again.

    1. Because our schematic design is about to freeze, and because of the layout, we don't want to put pull-up resistors.

    2. But because our understanding of DS is not deep enough, we came to you to consult if there is a way to choose RGMII mode without using hardware pull-up.

    3. See your previous reply that you recommend using register configuration to select RGMII mode

    4. Based on the above, if you can confirm that our current solution (that is, do not place a pull-up resistor and use a register to select RGMII) is no problem, we are ready to use this solution for outsourcing.

    Thanks

  • 0 in reply to Francis Pan
    TI__Mastermind 24135 points

    Hi Francis,

    Yes, RGMII mode should be changed through the register.

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 10 points

    Hi Hillman,

    Thanks for your reply.

    There is one more question I want to ask. At that time, we asked your colleague, and he sent us a screenshot like the one below.

    I searched the current specification and couldn't find this sentence.

    What does this "Faster bring up times" mean? Means faster initialization? What exactly does this time refer to?

    BR

    Francis Pan

  • 0 in reply to Francis Pan
    TI__Mastermind 24135 points

    Hi Francis,

    I am not sure if I understand you problem correctly. There are some other timing requirement come before the bootstrap latch in which you can see it on the 7.7 timing diagram in the datasheet. Reading the strap pin will come before the register read and write. It is totally safe to strap the pin first before read and write the register on MDIO.

    --

    Regards,

    Hillman Lin