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DP83867E: RX_CTRL Boot Strapping Pin

joe lindula
Mastermind 6940 points
Part Number: DP83867E

Hello, I am using the DP83867E on my custom board and we have unintentionally put RX-CTRL strapping pin in only Mode 4. This will disable Auto Negotiation. I need to put the pin in Model 3 but unfortunately I did not put in  the design for Rlo.

I was looking over page 38 in the data sheet and it has the following:

When I go to page72 to look at the Configuration Register bit 7 it shows:

Bit 7 is shown to be Reserved and the default value is 0.

Does this mean the device will set Auto Negotiation to be enabled?

Thank you

Joe

  • 0
    Mastermind 6940 points

    Oops, I should have noted that I removed R532 thinking that would enable Auto Neg but that would mean a Mode of 1 for RX_CTRL but that is not a value mode for this pin. What would happen then?

    Thank you

  • 0 in reply to joe lindula
    TI__Expert 3595 points

    Hi,

    I believe you may be looking at a different or incorrect version of the datasheet. The one online has reg 0x31 on page 75 and has the correct bit descriptions.

    You could also replace that resistor with a 26kOhm one and the voltage divider result would be the same as Mode 3. (feel free to double check my math)

    As the datasheet says though, Mode 1 will not give a valid result for auto negotiation. 

    Thanks,

    Lysny

  • +1 in reply to Lysny Woodahl
    Mastermind 6940 points

    Hello, thank you for responding to my message.

    Here is my math

    VDDIO = 1.8V

    Vmin = 1.8 * 0.225 = 0.405V
    Vtyp   = 1.8 * 0.255 = 0.459V
    Vmax = 1.8 * 0.284 =  0.511V

    Pick Rhi = 26.2K

    Vtyp = [9K/(9K+26.2K)]*1.8 = 0.46V

    I'll try to find a 26.2K resistor.

    Thank you