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TCAN1044A-Q1: Do we need pull up resistor for the RX/TX?

zhiyuan zhang
Intellectual 620 points

Part Number: TCAN1044A-Q1

Hello expert,

    We are using TCAN1044ADRBRQ1,do we need pull up resistor for the RX/TX? From the datasheet it seems that RXD can output high/low level voltage without external pull up, but I can't find the Vol and Voh in the datasheet.

  • 0
    Intellectual 620 points

    Addition question:

        What is the BUS state when power up and before MCU finish the initialization(MCU TX RX STB is high impedance),if no pull up resistor on the TX/RX/STB? We want to avoid the unexpected dominant state on the BUS

  • 0 in reply to zhiyuan zhang
    TI__Guru 74922 points

    Zhiyuan,

    Pull-up resistors on TXD and RXD are not needed, but they do establish a known state on the pins prior to the entire system starting up. And since it sounds like that's a concern for the customer, it would be good to include them. 

    If you look at the block diagram you've shared, there are internal pull-ups on both TXD and STB. This allows for TXD and the bus to stay recessive, and for the device to be in Standby mode to avoid any bus activity prior to the MCU booting up.

    Please let us know if you have any other questions.

    Regards,

    Eric Hackett