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DP83630: 100Mb Length Detect Register

Shota Mago
Expert 8130 points
Part Number: DP83630
Other Parts Discussed in Thread: DP83865

Hi team.

My customer has been using DP83630 and provided some questions regarding 100 Mb Length Detect Register.

  1. It seems that the default value of the CABLE_LEN register is 0xFF, but what does the register show when a cable of 1m or less is connected?
    e.g. In case that 20cm cable is connected, does the register value become 0x01(realistically, it would be around 0x00~0x05 because of accuracy)?
    Or does it show 0xFF(cable length can't be determined)?
  2. What is accuracy of cable length estimation?
    Is it ±5m like DP83865?

I'm looking forward to hearing back from you.

Best regards,

Shota Mago

  • 0
    TI__Mastermind 18425 points

    Hi Shota,

    For DP83630, it is expected that for short cables, the value would be between 0x00-0x05. However in order to confirm this we would need to review validation data from when the device was developed. This is a little difficult because the device was developed a while ago. Has the customer tested this on their board? What is the value that they observed? This also applies for the accuracy information as it is not recorded in the datasheet.

    -Regards

    Aniruddha

  • 0 in reply to Aniruddha Khadye
    TI__Prodigy 580 points

    Our customer explained the background about this question as follows.  

    there are 3 types of cable( same wire and sane connector) of  0.9m, 3m, 10m to connect the systems.

    They found it that  link up speed of 0.9 m cable are different from 10 m cable.

    (0.9m of cable is slower than 10 m cable.it depends on cable not system)

    They suspect the quality of 0.9m cable and tried to check whether quality is good or bad by using the DP83630 cable length measurement.

    As the result of it , DP83630 shows following response.   

    10m cable → about 0x0F (15m)
    0.9m cable → 0xFF (not measurable)

    since in the case of extremely short cables (for example 1 m or less) they don't know which number is correct ( 0x00 or 0xFF)

    If the short cable is detected as 0m as you commented, 0.9m cable may have any problems.

    How do you think about it ?

    If you know better way to judge cable quality by using register of DP83630.please let us know.

  • 0 in reply to Tohru Sakuma
    TI__Mastermind 18425 points

    Hi Shota, Tohru,

    I see the someone from our team is already helping on the same topic in a different thread :https://e2e.ti.com/support/interface/f/138/t/911787

    I will close this thread to avoid duplication.

    -Regards

    Aniruddha