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DP83869HM: Data conversion between Ethernet MACs

Hitoshi Maeda
Prodigy 100 points

Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

As shown below, I would like to connect two MACs by converting RGMII ⇔ SGMII using the DP83869HM.
Is this possible?
If it is possible, which should I use—Bridge Mode or Media Converter Mode?

 

image.jpg

  • 0
    TI__Guru**** 189651 points

    Hi,

    You would use the Bridge Mode in this case. Please see this e2e thread on how to enable this function.

    Thanks

    David

  • 0
    Prodigy 100 points

    Dear Support Team,
    I have an additional question.
    In the configuration SoC (MAC) – DP83869HM – SoC (MAC), both SoCs operate only in MAC mode.
    In this case, wouldn't the link become MAC-to-MAC communication, which is normally not possible?
    The SoC we are using cannot be configured in PHY mode.
    Therefore, I do not understand why the configuration SoC (MAC) – DP83869HM – SoC (MAC) is considered valid.
    Conceptually, is the following understanding correct?
    SoC (MAC) – [PHY – LAN cable – PHY] – SoC (MAC)
    and the part in brackets […] corresponds to the DP83869HM?

  • 0 in reply to Hitoshi Maeda
    TI__Mastermind 26771 points

    Hi Maeda-san,

    Hitoshi Maeda said:
    Conceptually, is the following understanding correct?
    SoC (MAC) – [PHY – LAN cable – PHY] – SoC (MAC)


    Your understanding is correct. Essentially, we use register settings mentioned in the E2E thread to make both MAC think they are linked via Ethernet. 

    Best,
    J

  • 0 in reply to Hitoshi Maeda
    Prodigy 100 points

    Dear TI Support Team,
    I would like to confirm how to configure MAC‑to‑MAC communication with the DP83869HM using external strap pins only (no register writes), and whether any additional register settings and 125‑MHz clock connections are required.

    1) Target topology
    MAC (RGMII) ⟷ DP83869HM ⟷ MAC (SGMII)
    We would like to use Bridge mode with only external pins if possible.

    2) Planned strap settings (external pins only)
    ① Set to “RGMII‑SGMII Bridge Mode”
     OPMODE[0] — pin 22 (JTAG_TDO / GPIO_1): High
     OPMODE[1] — pin 36 (RX_D3) : High
     OPMODE[2] — pin 35 (RX_D2) : Low
    ② Select direction “SGMII to RGMII (SGMII: MAC I/F, RGMII: PHY I/F)”
     MIRROR_EN — pin 38 (RX_CTRL): Low


    *Q‑A. With the above strap states alone, is MAC‑to‑MAC bridging fully supported without any register access?

    3) About the following register settings shown in E2E thread
    (Reference: e2e.ti.com/.../3385960 )
    REG(0x170) = 0x0800 # Activate CLK_OUT at 125 MHz
    REG(0x00C6) = 0x0010 # CLK_OUT (PLLCTL)
    REG(0x0C00) = 0x0140 # BIT12='0' => disable autoneg

    *Q‑B. Are these register writes mandatory for MAC‑to‑MAC bridging, or only required for specific cases?
             If mandatory, could you clarify why each setting is needed (e.g., which use‑cases require 125‑MHz CLK_OUT, when to disable autoneg, etc.)?

    4) Requirement and destination of 125‑MHz clock
    *Q‑C. Must the 125‑MHz CLK_OUT from the DP83869HM always be connected to any MAC in bridge operation?
              If required, should it be connected to the SGMII‑side MAC, the RGMII‑side MAC, or both?
               If the intended destination MAC cannot accept this clock, are there any side effects or loss of function we should expect?

    5) Additional constraints in Bridge mode
    We are aware that in both Bridge modes, PRBS mode is not applicable.

    *Q‑D. Are there any other Bridge‑mode‑specific limitations we should consider (e.g., LED link indication behavior, Auto‑Negotiation behavior, speed/duplex constraints)?
             Thank you in advance for your guidance.

  • 0 in reply to Hitoshi Maeda
    TI__Guru**** 189651 points

    Hi,

    The strap configuration for RGMII-to-SGMII Bridge mode is shown below. This will enable DP83869 into the RGMII-to-SGMII Bridge Mode.

    For Q-B, does the SGMII MAC support Auto Negotiation? If the MAC does not support Auto Negotiation, then you have to write to REG(0x0C00) = 0x0140 # BIT12='0' => disable autoneg to disable Auto Negotiation. 

    For Q-C, it depends on the MAC requirement. If MAC requires additional clock for phase/frequency synchronization, then you can use DP83869 CLK_OUT as an option.

    For Q-D, LEDs, if used, indicates status on the RGMII side in the Bridge Mode.

    Thanks

    David