is external pull-up ready needed for push button?

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hi,

just wondering what's the purpose of external pull-up when there is internal pull-up available on GPIO?

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In what context? Any specific external pull-up you're looking at or is this a general question?

For a push-button the internal pull-up might do just well, but IIRC older AVRs did not have pull-ups on all pins. In other cases you need a stronger pull-up than the internal one (eg. if something external to the AVR is pulling down weakly you need something that pulls up stronger than that).

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ok, got it.

But what's value of UC3B's internal pull up? 20K?

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Oooops. Didn't realise that I was responding in an AVR32 forum. Those are off limits for me...

Quote:

But what's value of UC3B's internal pull up?

Doesn't AVR32s have data sheets? :shock: (OK, so I had to d/l one and alas it is specified as TBD. To Be Determined? Uh!)

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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Provided it pulls up internally to Vcc, just configure it with a pull-up enabled, and ground it with a ~30Kb resistor. Measure the voltage on the pin and calculate the built-in pull-up value out of that and the pull-down you used.

Artyom

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yes, right, thanks.

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Perhaps this is a design paradigm but--

IMHO, it is always beneficial to include a pull-up or pull-down on a pin if you need to ensure that the pin has a specific state on system startup. It may not be necessary, but it ensures that the system remains stable (i.e. pull-up resistor on #CS of SPI device).

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yes, i understand this, my main consideration is the extra power consumption these resistors introduced in my low power design.

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i got this from ATMEL for UC3B:

the pull-up value :
Typ: 19k
Max: 25k
Min: 13k