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Question about the internal pull-up and pull-down resistors of C6472

haopeng han
Expert 1120 points

Hi,

I have a question about the internal pull-up and pull-down resistors of C6472's GPIO. The GPIO signal pins GP[6:14] are shared with boot mode select function, whitch is determined by the value sampled at the power-on-reset. My question is, are these internal pull-up/down resistors enough for boot mode select? For example, if my boot mode is RIO4 ,BOOTMODE[3:0]=1110, can I just use the internal pull-up of GP[7:9] to form the '1's and use an external 1K pull-down to be the '0'?

Any help / suggestion would be greatly appreciated!

B.R.

Han

  • 0
    TI__Guru 64440 points

    My general guidance to individuals, regardless of the answer to your question about the strength of the internal pullup/pulldowns, is to use external pull resistors for this purpose.  This is especially true if you are using these I/Os for other purposes after reset, which means you have board traces on these signals.  The internal pullup/pulldowns are weak and meant to keep the pin stable to a level if that pin is not routed anywhere on the board.  They are not strong enough to address any noise that may be coupled on that trace and I certainly would not want your boot mode selection to be determined by potential noise.

    Also, you may want to consider alternate boot modes for either development and/or manufacturing.

    To answer your question, in the Terminal Functions section of the datasheet (Section 2.7) there is a footnote indicating the internal pullup/pulldown is equivalent to a 30K ohm, or 100 uA.

     

  • 0 in reply to BrandonAzbell
    Expert 1120 points

    Hi Brandon,

    Thank you for your answer!

    I got your ideal. What I also want to know is, are these GPIO pull up/down resistors enabled before the sampling of the GPIO pins after the power-on-reset?  Are these GPIO pulls effective all the time? (since other pull resistors can be enabled/disabled) Thank you!

    B.R.

    Han

  • 0 in reply to haopeng han
    TI__Guru 64440 points

    Yes, these GPIO pullup/pulldown circuits will be enabled before the sampling of the GPIO pins upon the power-on-reset.  These particular pullup/pulldowns are effective all of the time.