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DP83848YB PIN CONTROL

hakyung cha
Prodigy 20 points
Other Parts Discussed in Thread: USB-2-MDIO

I want to use that device as Auto-Negotiation Pin Control Forced Mode I tried to change the electric circuit.

First I removed LED and 1.5 kΩ resistor. (R775, R776, LED510, LED517)

and The value on AN_EN(LED_ACT/COL) pin is set by connecting the input pins to GND (0) through 2.2 kΩ resistor.(R246, R247)

but AN_EN(LED_ACT/COL) pin keep on being measured high(+3.3V). What is the problem and I want to know how to use the device as Auto-Negotiation Pin Control Forced Mode.

  • 0
    TI__Mastermind 19780 points

    Hello Hakyung,

    If I understand you correctly, you want to use the DP83848 in Forced mode. Which speed would you like to force the link? 10M? 100M?

    You did the correct steps to use forced mode. When you connect the pins to ground using a resistor, the GROUND voltage is only tested by the PHY at start-up. When the PHY checks the pin voltage, it then puts 3.3V on the pin. This is normal.

    Use an oscilloscope to look at the pin when RESET pin is pulsed and you will see the AN_EN pin go low and then high again.

    Have you looked at the registers to see if the auto-negotiation enable bit[12] in the register address 0x0 has been changed by AN_EN pin?

    Best Regards,

  • 0 in reply to Rob Rodrigues
    Prodigy 20 points

    I'm grateful for your quick response.

    But your response different from what I want to know.
    I only want to use Forced mode(-10BASE-T, Half-Duplex) as shown in the data sheet.


    So I was connected to Ground instead of 3.3V in order to change Advertised Mode to Forced Mode.
    However, When I set a laptop to Auto and the board connects an Ethernet, the notebook's link rate was 100M and AN_EN was a HIGH.
    If this is not normal, I want to know what the problem.

  • 0 in reply to hakyung cha
    TI__Mastermind 19780 points
    Hi Hakyung,

    If you tie the LED pins to ground, the LED driver will become active low driver. For AN_EN this means if you don't have activity on the line, you will get a HIGH voltage. Testing the voltage any time after 270ms is invalid because the pins have already transitioned to their main function. In this case AN_EN, AN1, AN0 change from STRAP pin to an LED pin.

    Linking in 100M is odd if your PHY is set to forced 100M mode. Please read register 0x0 on the PHY and make sure bit[12] is set to 0. If you don't have a method to access MDIO registers, you can try using the USB-2-MDIO tool here on ti.com/tool/usb-2-mdio. This requires an MSP430 LaunchPad.

    Best Regards,