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TCA9555: Pull-up resistors by default?

Dejan Hrovatin1
Intellectual 380 points
Part Number: TCA9555
Other Parts Discussed in Thread: TCA9535

Tool/software:

Hello,

I just would like to ask for clarification - when the ports of TCA9555 are configured as inputs, pull-up resistors on those pins are enabled by default, am I right? So, when I read status of those pins, it will be high, till they are not driven low by external signal?

In the datasheet of TCA9555 is written: The TCA9555 is identical to the TCA9535, except for the inclusion of the internal I/O pull-up resistor, which pulls the I/O to a default high when configured as an input and undriven.

What does word undriven means in sentence above?

Many thanks, Kind regards, Dejan.

  • 0
    Guru 316690 points

    "Undriven" means that they are not driven by an external signal.

    As shown in figure 23, the pull-up is always active.

  • 0
    TI__Mastermind 47328 points

    Hi Dejan,

    Dejan Hrovatin1 said:
    I just would like to ask for clarification - when the ports of TCA9555 are configured as inputs, pull-up resistors on those pins are enabled by default, am I right? So, when I read status of those pins, it will be high, till they are not driven low by external signal?

    Yes you are correct here. 

    Dejan Hrovatin1 said:
    In the datasheet of TCA9555 is written: The TCA9555 is identical to the TCA9535, except for the inclusion of the internal I/O pull-up resistor, which pulls the I/O to a default high when configured as an input and undriven.

    Yes this is correct. 

    Dejan Hrovatin1 said:
    What does word undriven means in sentence above?

    As Clemens suggested already, an external signal by another device in the system. 

    Regards,

    Tyler