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DS92LX2121 / DS92LX2122 GPIO

Bradley Helsel
Intellectual 260 points
Other Parts Discussed in Thread: DS92LX2121, DS92LX2122

Hi,

If the Serializer (DS92LX2121) is not physically connected to the Deserializer (DS92LX2122) what can I expect the states of the GPO[0:3] pins to be at the Serializer?

My system has an option were the display is not used and the GPO pins are being used for system status. I want to ensure that these outputs will provide the state that I am expecting in this configuration.

Thank you.

Bradley Helsel

  • 0
    TI__Genius 13475 points

    Bradley

    The power-up default state for the GPOs is LOW, but this can be overwritten either via the I2C bus on the serializer, or via the backchannel from the deserializer.

  • 0 in reply to Mark Sauerwald88474
    Intellectual 260 points

    Mark,

    My system has two "boxes"; a controller box that has the processor board that contains the Deserializer and a display box that has a touch screen display and the control board with the Deserializer. Normally  the display box is connected to the controller through a cable. There is however an option to not have a display, meaning the the Serializer will not have a Deserializer connected to it during normal operation. If the system is powered up without the Deserializer connected, will the GPO's on the Serializer still default to LOW? Do I need to provide a pull down resistor to ensure this state?

    Thanks.

    Bradley Helsel

  • 0 in reply to Bradley Helsel
    TI__Mastermind 29655 points

    Hi Bradley,

    Apologies for the slow response.

    If there is no input being provided to the serializer GPOs, then the default output should be low due to an internal weak pulled-down. However, if there happens to be some large amount of inadvertent noise coupling into the serializer, then it is possible that the GPO may show unwanted signs of activity. If the space is available, I recommend using pull-downs to ensure the state.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Intellectual 260 points

    Hi Michael,

    Can you explain what you mean by "...large amount of inadvertent noise coupling into the Serializer..."?

    If it is the SERDES channel (because it is essentially floating with no Deserializer connected) then that would mean that the output is switching between being an output to being a weak low and a pull-down resistor would not have any effect.


    Thanks,

    Brad.

  • 0 in reply to Bradley Helsel
    TI__Mastermind 29655 points

    Hi Brad,

    If you would like a larger threshold voltage for valid GPO signal to avoid passing noise as an output and ensure the state of the GPO, you can add an additional pull-down resistor at the output, since it will combine in parallel with the internal pull-down. It is more of an insurance feature than a requirement, since there are already internal pull-downs.

    Revisiting your comments, I agree with you that if the output is already switching well beyond the threshold voltage between active and inactive (weak-low), adding a large pull-down resistor will not have any effect.

    Thanks,

    Michael