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DP83867IR: The communication is unstable with short cable

Atsushi Takahashi
Expert 1415 points
Part Number: DP83867IR

Tool/software:

Hi Team,

In the system using DP83867IR, the communication is unstable with short cable(1m to 2m).

Concretely, it may take a long time for the link up, or an error may occur after the link is established, causing auto-negotiation to be performed again.

Sometimes the link may not be established.

The communication is stable with long cables(20m).

According to DP83867 Troubleshooting Guide(SNLA246C), It says short cables at 1m or less in length for your device can experience signal quality issues.

Please see section 3.1, Improving Link-up Margins for Short Cables.

https://www.ti.com/lit/an/snla246c/snla246c.pdf

Following the data sheet(See attached), section 8.6.12, the customer tried to write to the register, but it is not writing correctly.

For example, they tried to write 5555 to register 0x0115 and then read it back, the result was DDDD.

However, this data sheet may be out of date.

1) Please tell me the correct way to write to these register.

2) Most of the registers mentioned in Section 3.1 of this application note are not described in the datasheet. Could you provide more details about these registers?

Best Regards,

dp83867ir.pdf

  • 0
    TI__Expert 6425 points

    Hi Takahashi,  

    Some of the registers mentioned in the section 3.1 of the troubleshooting guide, for improve link margins with short cables, are extended registers. There is a particular way we need to access these registers. This FAQ explains the process quite well. Any register after the register value 0x1F would need to be written or read this way.

    Extended Register Space Access FAQ

    Using this method and following the steps outlined in the troubleshooting guide should help with this issue.

    Some of these registers are not public, but for internal testing, which is why they are not listed in the datasheet. Regardless, these register settings should help with the issue you're facing.

    Best Regards,

    Vivaan