• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 614 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DP83867CR: DP83867IRRGZ auto-negotiation issues

Duoduo Cheng
Expert 3050 points
Part Number: DP83867CR

When debugging the auto-negotiation function of DP83867 , if the device is connected to the H3C 100M exchanger, it can be automatically negotiated to 100M. If the device is directly connected to the PC network port by using the 100M straight-through cable, the computer network port (supporting Gigabit/100M/Ten megabytes) is configured for auto-negotiation and  the status of the computer network port is 100M. But the device still displays 1000M. Why is it not auto-negotiated to 100M?

  • 0
    TI__Mastermind 19780 points
    Hi duoduo,

    What do you mean by 100M straight-through cable? Do you mean the cable only has 2 twisted pairs in it?

    Best Regards,
  • 0 in reply to Duoduo Cheng
    TI__Mastermind 19780 points
    Hi duoduo,

    In this case there is a problem with auto-negotiation over 2 twisted pairs.

    1000M mode requires all 4 pairs to be present to transmit data, but only 2 pairs are used for auto-negotiation. It is possible to get auto-negotiation to complete and show 1000M link even though data isn't possible over 2 pairs only.

    To fix this issue, the feature called "speed optimization" on the DP83867 must be enabled. When speed optimization is enabled, the DP83867 will detect no activity on the missing channels and will fall back to 100M speed.

    Please see the description in the DP83867CR datasheet section 8.4.6.6 Speed Optimization.

    Also see the speed_opt_en bit in register address 0x0014 in the datasheet.

    Best Regards,