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DS125DF410: CDR Reset

Lidong Yu
Intellectual 1756 points
Part Number: DS125DF410

Is CDR Reset mandatory in DS125DF410SQ ?

I only set the regiser like as below.

 

1. Set 0xff register to 0x0c

2. Set bits 5:4 of register 0x36 to '2b11

3. Set 0x2f register to 0xf6

4. Set 0x15 register to 0x42

There was no problem with the above settings.

Please let me know the information.

Thank you.

  • 0
    TI__Mastermind 36443 points

    Hi,

    When making any changes to the VCO, it is recommended to assert and release CDR reset.  You could follow the following writes in order to do this:

    Register Address Register Value Register Mask Description
    0xFF 0x0C 0x0C Broadcast to all channels
    0x0A 0x0C 0x0C Assert CDR reset
    0x36 0x30 0x30 Enable 25Mhz reference clock
    0x2F 0xF6 0xFF Select Data Rate
    0x15 0x42 0xFF Set driver de-emphasis
    0x0A 0x00 0x0C Release CDR reset

     Thanks,

    Drew

  • 0 in reply to Drew Miller1
    TI__Intellectual 1756 points

    Are VCO changes included in the REGISTER below?

    1. Set 0xff register to 0x0c

    2. Set bits 5:4 of register 0x36 to '2b11

    3. Set 0x2f register to 0xf6

    4. Set 0x15 register to 0x421. Set 0xff register to 0x0c

    I need to set the CDR reset ? or not ?

  • 0 in reply to Lidong Yu
    TI__Mastermind 36443 points

    Hi,

    Yes, it is recommended to use CDR reset.  Setting register 0x2F to 0xF6 sets the data rate by adjusting the VCO frequency and dividers.

    Thanks,
    Drew

  • 0 in reply to Drew Miller1
    TI__Intellectual 1756 points

    The configuration sequence you answered is different from the CDR reset sequence of the datasheet and programming guide.

    Answered sequence:
    1. set 0xa register to 0xc
    2. set 0xff regisrer to 0xc
    3. set 0x2f reigster to 0xf6
    4. set 0x15 register to 0x42
    5. set 0xa register to 0x0

    programming guide:
    1. set 0xff register to 0xc
    2. set 0x00 register to 0x4
    3. set 0xa register to 0x0c
    4. set 0x2f register to 0xf6
    5. set 0x15 register to 0x42
    6. set 0xa register to 0x0

    datasheet:
    1. set 0xff register to 0xc
    2. set 0x2f register to 0xf6
    3. set 0x15 register to 0x42
    4. set 0xa register to 0xc
    5. set 0xa register to 0x0

    which sequence should I set?

  • 0 in reply to Lidong Yu
    TI__Mastermind 36443 points

    Hi,

    Both the sequence from the programming guide or the datasheet should work.  I am going to update the sequence in my original response to better match the procedure in the programming guide in case anyone references this in the future.  I think it's important to broadcast to all channels (0xFF = 0x0C) before asserting CDR reset, so thank you for bringing this to my attention.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    TI__Intellectual 1756 points

    Now we use 2 retimer chips on our card.
    Chip A : PHY -> Retimer -> SFP+ (TX Line)
    Chip B : SFP+ -> Retimer -> PHY (RX Line)

    * TEST Configuration
    (-------------Board A--------------) (-------------Board B--------------)
    PHY -> Retimer -> SFP+ -----> Optic cable ----> SFP+ -> Retimer -> PHY
    (TX Line) (RX Line)

    - Test Case 1
    When I set the CDR reset and release on board A Retimer, we got a RX CRC error on board B.
    At this time, if we make a link down and up, this CRC error is disapear.

    - Test Case 2
    When I set the CDR reset and release on board B Retimer, It's good working without CRC error.

    My question is, if I do not CDR reset and release setting to retimer of board A , any problem will be happened?

    If it's ok, I would like to remove CDR reset sequence when other register seting.

  • 0 in reply to Lidong Yu
    TI__Mastermind 36443 points

    Hi,

    Just to confirm, when you set/release the CDR reset on board A, do you continue to get RX CRC errors on board B until you do link down and up, or do you just get CRC errors during the reset and release procedure?

    CDR reset/release is used to allow the retimer VCO to match the data rate after changing the VCO settings.  It is recommended to set and release the CDR reset after changing the VCO settings in order to allow the VCO to adapt to a new data rate.  The impact of not doing this would be that you may be unable to achieve CDR lock, however if you have not had issues achieving CDR lock, than it may be unnecessary in your case.

    Thanks,
    Drew

  • 0 in reply to Drew Miller1
    TI__Intellectual 1756 points

    in my board case, continue to get RX CRC errors on board B until you do link down and up.

  • 0 in reply to Lidong Yu
    TI__Mastermind 36443 points

    Hi,

    Thank you for the clarification.  After setting/releasing CDR reset on board A, have you tried following this by setting/releasing CDR reset on board B?  Do you continue to get CDR errors after doing this?

    Also, which adapt mode are you using on the retimer?

    Thanks,

    Drew