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DP83869HM: Link status is failed on writing to BMCR register of DP83869HM

Manisha Narayana Gowda
Intellectual 290 points
Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869

Hello everyone,
I am using a DP83869HM Phy device.
I am trying to write to the BMCR Register, where I need auto-negotiation to be disabled. But on writing to the register BMCR, the link fails each time.
How can I write to this register, I tried writing different values to BMCR, (where auto-negotiation is always off).
If there any prior configuration needs to be done write to this register.
Thanks In advance

Manisha

  • TI__Mastermind 19621 points

    Hi Manisha,

    Could you tell me why you want to disable auto-negotiation? 

    Disabling Auto-negotiation puts the PHY into a Forced Speed (speed is configured through bits 13 & 6 of Reg 0x0). For Link to work, both parties need to be in the same forced speed or both have auto-negotiation enabled. Link will never be established if one PHY has Auto-neg on and the other end of the cable has a PHY in a forced speed.

    We strongly recommend keeping auto-negotiation enabled. If you want to configure a certain speed, we recommend de-advertising those speeds from registers 0x4 & 0x9.

    Regards,

    Alvaro

  • in reply to Alvaro (Al-vuh-roe) Reyes
    Intellectual 290 points

    Hello Alvaro
    Thanks for the explanation.

    Auto negotiation need to be disabled for my project. Speed duplexity need to be configured.

    Now I am using the ethernet/CAN interface  which has ethernet port in it.
    So the PHY layer  DP83869HM and ethernet/CAN interface are running without auto  negotiation and speed of 100Mbps.

    When I am writing to 0x140 to the register of adress0x0 ( BMCR Register), there is no link seen. 
    De-advertising those speeds from registers 0x4 & 0x9 is also done.
    What can be the reason, is there any configuration need to be made?

  • in reply to Manisha Narayana Gowda
    TI__Mastermind 19621 points

    Hi Manisha,

    Firstly, I want to confirm that the DP83869 is capable of operating in Forced 100 Mbps mode.

    The only register write for forcing 100 Mbps is Reg 0x0 = 2100.

    Your register write of 0x0 = 0x0140 is forcing 1000 Mbps, which we do not support.

    Regards,

    Alvaro

  • in reply to Alvaro (Al-vuh-roe) Reyes
    Intellectual 290 points

    Hi Alvaro
    Thanks for the info.
    This worked for me
     
    Regards
    Manisha