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DP83867E: DP83867E going into mirror mode on powerup

Jessica Urbano
Prodigy 60 points
Part Number: DP83867E

Hi, we are using the DP83867E on our board, and we have noticed some strange behavior when we power-on while plugged in to a 10/100 switch.  

If we are plugged into a switch at power up, we will not get a link.  I noticed that in Configuration Register 4 (Address 0x0031) the PORT_MIRROR_EN bit was set to 1.  If I cleared this bit a link was established.

However, I did not see this issue when I powered on without the board plugged in to a switch, or if it was plugged in to a gigabit switch.  I know this mode is set by the strapping pins (particularly LED_0) on power up and reset, could it be an issue there?  Not sure why plugging in to a switch would have an impact as the LED_0 pin should have an internal pulldown on it. 

We currently have the LED_0 pin going to a FDME1024NZT FET that drives an LED.   Any feedback on the current set up and would could be causing this issue would be appreciated! 

  • 0
    TI__Mastermind 18425 points
    Hi Jessica,

    You are correct that LED_0 controls mirror mode on the PHY and that it has a internal pull down resistor. However the resistor is weak in the range of 9kohm. There can be cases where the internal pull down gets over-powered by external devices. It would be difficult to pin point a cause of this happening since it depends on the whole system. Does your DP83867E board perform a Reset of the PHY after the board powers up?

    -Regards
    Aniruddha