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TLIN1021A-Q1: question about TXD pin configuration

Jay wang
Expert 3191 points
Part Number: TLIN1021A-Q1

Tool/software:

hi expert 

i saw the following words in datasheet. i have two questions.

Q1: according to datasheet description, TXD pin can be pull-up by using pull up resistor. which is circuit more used widely, using pull-up resistor or NO pull-up resistor?

Q2: TXD usually is connected to MCU IO. And MCU IO can be configurated as pull-up mode in MCU internal. if so, whether is external pull-up resistor needed to add to TXD pin?

  • 0
    TI__Mastermind 27660 points

    Hi Jay,

    Pull-up on TXD is not needed. TXD already integrate weak pull-down to ensure a known state if the pin is floating.

    There is also no issue with a pull-up for TXD. This would still ensure a known state when left floating. So there's no right or wrong here, it's up to customer.

    Regards,

    Sean

  • 0 in reply to Sean Guo
    TI__Expert 3191 points

    hi  Sean

    thanks for your quick reply. i have some further question and let me describe it more clearly.

    Q1:i have know adding external pull-up resistor on TXD is no right or wrong. According to datasheet "If an external pull-up resistor is added to the TXD pin to the microcontollers IO voltage then TXD is pulled high to indicate a remote wake-up event", in other words. if designer want to know whether remote wake-up event happen, they need to add an external pull-up resistor on TXD pin, right? like the following shown?

    Q2:(further question about above picture) whether can designer use MCU IO internal pull-up resistor to replace external pull-up resistor ?

    Q3:after first LIN power up, VSUP > UVSUP and EN = Low, TXD is in weak pull-down or Hard pull-down?

  • 0 in reply to Jay wang
    TI__Mastermind 27660 points

    Hi Jay,

    1. Correct, if they want to distinguish remote wake-up and local wake-up, they can add this external pull-up to TXD. If they don't have this requirement, let's say LWU is not used or they don't need to detect the wake-up source (WUP or LWU), then they can just rely on RXD pulling low in standby mode to indicate a wake-up event.

    2. Yes they can.

    3. TXD is hard pull-down. Initial power up (or power cycling the device) is essentially local wake-up.

    Regards,

    Sean

  • 0 in reply to Sean Guo
    TI__Expert 3191 points

    thanks for your support Sean

  • 0 in reply to Sean Guo
    TI__Expert 3191 points

    hi Sean

    further question about above Q3(TXD is hard pull-down. Initial power up (or power cycling the device) is essentially local wake-up.)

    customer finds TXD become high from low without LIN receiving any wake up after they configure MCU GPIO as PULL-PULL. according to your reply, if TXD is hard pull-down, TXD should be LOW.

  • 0 in reply to Jay wang
    TI__Mastermind 27660 points

    Hi Jay, 

    Can they capture EN signal? Did EN stay at low?

    Regards,

    Sean

  • 0 in reply to Sean Guo
    TI__Expert 3191 points

    hi Sean

    YES, EN pin is always low

  • 0 in reply to Jay wang
    TI__Mastermind 27660 points

    Hi Jay,

    I tested it with an external 10K pull-up on TXD, the result is the same as your customer's, TXD goes from low to high.

    So after power-on, TXD will have a weak pull-down if EN = low. The only case for hard pull-down is wake up by the WAKE pin.

    Regards,

    Sean

  • 0 in reply to Sean Guo
    TI__Expert 3191 points

    hi Sean

    based on your current hardware set-up, if LIN receive a remote wake-up, what is the TXD states? weak pull-down?

    if so, this LIN cannot figure out a remote wake-up or first power-up, right?

  • 0 in reply to Jay wang
    TI__Mastermind 27660 points

    Hi Jay,

    A remote wake-up will weakly pull down TXD.

    If the device enters standby mode after power-up, there's no other indicator to distinguish remote wake-up or initial power-up.

    Regards,

    Sean