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M4 Express: Actual resistance value of pull up/down
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M4 Express: Actual resistance value of pull up/down

by xanatos on Mon Jul 04, 2022 6:36 pm

Can't seem to find the actual resistance value of the pull up/pull down settings for digital inputs. ItsyBitsy M4 Express. Need to know actual values to figure into my calculations,

Thanks!

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Re: M4 Express: Actual resistance value of pull up/down

by dastels on Mon Jul 04, 2022 6:51 pm

It's not as simple as a resistance to Vcc or Gnd. See section 32.6.3 on page 818 of the SAM D5x data sheet. You can find a copy at https://www.mouser.com/datasheet/2/268/60001507A-1130176.pdf.

If you need to know/control exactly what the pull up/down is, don't enable the internal pull up/down and use an external resistor.

Dave

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Re: M4 Express: Actual resistance value of pull up/down

by xanatos on Mon Jul 04, 2022 7:53 pm

Thanks Dave. Page 818 is all about "OSC32KCTRL – 32KHz Oscillators Controller" - but I'm guessing it'll be in here somewhere :) I just need to be sure the pullups are in excess of 100k effectively. If not, like you said, I'll need to use external pull-ups/downs.

Thanks!

Dave

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Re: M4 Express: Actual resistance value of pull up/down

by dastels on Mon Jul 04, 2022 8:14 pm

I must have a slightly different version locally. Section 32 starting on pg 883.

Dave

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Re: M4 Express: Actual resistance value of pull up/down

by xanatos on Mon Jul 04, 2022 8:19 pm

Thanks Dave, I did find the section... trying to make sense of it now :)

Dave

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Re: M4 Express: Actual resistance value of pull up/down

by westfw on Mon Jul 04, 2022 10:37 pm

Actual values are down in the "Electrical Characteristics" pages (54.9 in my copy):
"Somewhere between 20k and 60k" is probably not what you were hoping for!
Screen Shot 2022-07-04 at 7.23.26 PM.png
Screen Shot 2022-07-04 at 7.23.26 PM.png (79.4 KiB) Viewed 49 times

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Re: M4 Express: Actual resistance value of pull up/down

by xanatos on Tue Jul 05, 2022 1:14 pm

LOL! Thanks for that. Yes - I'll definitely be using external pullups on the lines that I'm concerned with! :)

Dave

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