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TLK105 LED interface

Chris Woodyatt
Prodigy 130 points

It is unclear from the datasheet whether it is possible to configure the LED_LINK pin to source current. Figure 3-4 shows the pin sinking current through the LED. However, the LED Control Register bit 7 "LED Link Polarity" suggests that the pin's operation is configurable, but it is not clear if this is the case. Can anyone confirm the operation of this pin?

  • 0
    TI__Intellectual 1720 points

    Hi,

    Figure 3-4 is the correct method to connect the LED. Please notice that bit 7 Default is defined 'strap' which means it is defined by the board configuration you use connected to the LED pin. The bit is RW, however, changing the bit without the HW connected to the pin will not results with the required polarity changes. In order to change polarity both HW and the bit need to be changed. Again, since this is 'strap', you don't need to write the bit after you change the HW, only to do HW reset and the bit will automatically be updated with the correct polarity.

    Thanks & Regards,

    Oren

  • 0 in reply to Oren Shalita
    Prodigy 130 points

    Thanks for the clarification...it's a shame that the pin can't be configured to source current, perhaps that could be something you might do on future versions to enhance the flexibility of the device.

    Cheers,

    Chris

  • 0 in reply to Chris Woodyatt
    TI__Intellectual 1720 points

    Hi Chris,

    The LED can be configured as be both current source (LED pulled down) or current sink (LED pulled up),

    In the DS only the current sink example is presented .

    For a more detailed schematic for both option, please refer to the TLK EVM user guide, on page 9:

    http://www.ti.com/lit/ug/sllu155/sllu155.pdf

    Thanks & Regards,

    Oren 

  • 0 in reply to Oren Shalita
    Prodigy 25 points

    Hi Oren,

    i have a very similar question which gets partially answered by the EVM guide:

    I want the TKL10x pin to source the LED, and this can be done as shown in the guide on page 9.

    But if I connect the pull down resistor I "strap" the AN_0 low, which means I configure the TLK10x for Half-Duplex.

    But can I configure this pin to source the LED, active high, not adding any pull resistor (which leaves the internal pull up) so that AN_0 is 1. In other words from the datasheet I understand that if I dont't add any pull down or pull up resistor the pin should be active high and sourcing the LED on LINK GOOD, is this right ??? The datasheet is, in my opinion, really confusing about this! Also I understand that whatever hardware configuration I use, I will be able to re-configure it by software, is this true ???

    Best Regards,

    Alfonso

  • 0 in reply to Alfonso Zaccaria
    TI__Intellectual 1500 points

    Hi Alfonso,

    If you want the TLK to source the LED, it needs to be pulled-down.
    This configuration needs to be at the stage you release the reset pin, as the strap option is being sensed and sets the LED pin to be source/sink.
    If you want also the device in another configuration, different to the configurations set by the strap, use register writings to change the configurations.
    For example, if you set the AN_0 to be pulled-down, source to LED, to have FD configured you will need to write:
    1. Register 0x0001 (BMSR), bit 14 to value 1: "Device able to perform 100Base-TX in full duplex mode".
    2.  Register 0x0000 (BMCR), bit 9 to value 1: "Restart Auto-Negotiation".

    Leaving the strap unconnected will use the internal PU, configuring the device for full-duplex option, but this will make the device act as LED sink and not source.


    Thanks,
    Noam

  • 0 in reply to Noam Sadan
    Prodigy 25 points

    Hi Noam,

    your explanation is very clear. My doubts arised from the TLK 105/6L datasheet on page 66, LED Control Register (LEDCR) bit 7. In my opinion following information on the strapping value is missing:

    PU (strapping value logic 1) --> bit 7 = 0

    PD (strapping value logic 0) --> bit 7 = 1

    Else I would think strapping value logic 1 --> bit = 1 ....

    Thanks,

    Alfonso

  • 0 in reply to Alfonso Zaccaria
    TI__Intellectual 1500 points

    Hi Alfonso,

    I agree we need to add some information on the LED polarity mechanism.
    I will try to add this on our next datasheet version.

    Please let me know if you have any further questions.

    Thanks,
    Noam