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Original question:

DP83848I: How to configure LED_0/1 pin to drive bi-color LED?

DP83848I: Auto negotiation: LED Link Polarity

Jens Tyslik
Intellectual 1610 points
Part Number: DP83848I
Other Parts Discussed in Thread: DP83825I

Hi team, 

I received the following question:

I need to enable auto negotiation, so I have to strap LED 0 to gnd.

What is then the polarity of the LED-0 Link signal if I do not change anything in the registers?

According to datasheet table 37, the value for LED_Link_Polarity is 0x0. Does this also apply in the auto-negotiation mode?

thanks in advance!
Jens

  • 0
    TI__Intellectual 1610 points

    Hi, 

    I got a bit confused because there is also Table 90. Register_0x469_Register Register Field Descriptions with LED_1 and LED_2. There is no LED 1 in the pinout, is LED_1 a typo for LED_0?

    There is also Table 86. LEDCFG_Register Register Field Descriptions.
    It says "LED_2 Control:Selects the source for LED_1" I assume this is a Typo?

    There is also Table 89. SOR2_Register Register Field Descriptions
    It says "CFG_LED_LINK_POL 0x1 1 = LED_LINK is active high 0 = LED_LINK is active low"

    which is active high after reset.

  • 0 in reply to Jens Tyslik
    TI__Expert 5425 points

    Hi Jens,

    The DP83848I does not have an LED_0 pin or a register 0x469 listed in the datasheet. Are you referring to a different part?

    Regards,

    Adrian Kam

  • 0 in reply to Adrian Kam
    TI__Intellectual 1610 points

    Hi Adrian, 

    please excuse, I mixed things up. 

    The correct part number is DP83825I

    regards, 
    Jens

  • 0 in reply to Jens Tyslik
    TI__Expert 5425 points

    Hi Jens,

    1. When LED_0 is strapped to GND, the polarity of LED_0 will be active high. This change should be reflected when you read register 0x18. Auto-negotiation mode does not affect the polarity, only the strap or register write.
    2. This is not a typo, as other devices with LED_1 uses the same register. In this device, writing those LED_1 configuration bits will do nothing. LED_0 polarity is configured in register 0x18, under bit[7] "LED_Link_Polarity".
    3. Yes, it is a typo. It is suppose to say "LED_2 Control:Selects the source for LED_2".
    4. Reading this bit in Table 89 will indicate whether LED_0 is configured/strapped to an active high configuration or active low configuration. If you are strapping LED_0 to GND, then it should read active high.

    Regards,

    Adrian Kam