Pull-up resistors
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37ronal...@gmail.com
May 13, 2016, 12:00:48 PM5/13/16
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Are pull up resistors required for the GPIO pins when used as inputs or as outputs for the beaglebone black? I am using the beaglebone to drive a few n-channel MOSFETs. Thanks!
Chad Baker
May 13, 2016, 1:15:47 PM5/13/16
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The AM3358 has internal pullup/pulldown resistors available for GPIO
inputs. These can be enabled using the universal-io
"https://github.com/cdsteinkuehler/beaglebone-universal-io". If you
are using a current version of Debian, the device tree should
already be included. The github overview shows how to use
config-pin, the command "config-pin -h" shows how to engage the
pullup/pulldown resistors.
Chad
Chad
Are pull up resistors required for the GPIO pins when used as inputs or as outputs for the beaglebone black? I am using the beaglebone to drive a few n-channel MOSFETs. Thanks!
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William Hermans
May 13, 2016, 1:19:46 PM5/13/16
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Are pull up resistors required for the GPIO pins when used as inputs or as outputs for the beaglebone black? I am using the beaglebone to drive a few n-channel MOSFETs. Thanks!
Pull up/down resistors are typically "required" by the circuit. In your case where you're using a device that tends to be used as a switch. Leaving the circuit floating can cause unexpected behavior.
So, is it "required" ? No. Is it desired? Yes.
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William Hermans
May 13, 2016, 1:21:59 PM5/13/16
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Also, I'm not exactly an EE, but the one EE I do know, seems to prefer using external pull up/down resistors. Why, I'm not sure, but perhaps someone who is an EE can explain why.
Gerald Coley
May 13, 2016, 1:28:03 PM5/13/16
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If you need a pin to be hi or low at power up, and you can't afford to wait until the SW initializes the hardware, then you need to use a pullup or pulldown to make sure that pin is in the state you need. Some pins come up with the signals pulled hir or pulled lo. You should use those pins which have the default mode you need.
Also, these are weak pullups and pulldown resistors. They may not drive enough current to insure whatever is connected that it is indeed hi or lo on power up. You may need to add an external resistor to insure that it is where you want it to be.
Also note that the drive strength of the GPIO pins is limited. You need to use a resistor value that the processor can drive.
Gerald
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Harvey White
May 13, 2016, 2:45:17 PM5/13/16
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On Fri, 13 May 2016 10:21:52 -0700, you wrote:
>Also, I'm not exactly an EE, but the one EE I do know, seems to prefer
>using external pull up/down resistors. Why, I'm not sure, but perhaps
>someone who is an EE can explain why.
You can control the values for external parts. Not all processors or
>Also, I'm not exactly an EE, but the one EE I do know, seems to prefer
>using external pull up/down resistors. Why, I'm not sure, but perhaps
>someone who is an EE can explain why.
chips have internal resistors that can be enabled.
Example: cable tester, open drain outputs driving an input, chip
provided resistor 100K (not a processor)... That's rather high, and
susceptible to noise. 1K to 10K would be better, but would require
external parts.
lower the resistor value, more current flows, but the less susceptible
to noise you happen to be.
Harvey
>> *Are pull up resistors required for the GPIO pins when used as inputs or
>>> as outputs for the beaglebone black? I am using the beaglebone to drive a
>>> few n-channel MOSFETs. Thanks!*
>>> https://groups.google.com/d/msgid/beagleboard/81b4dd20-bdad-4034-b024-d71f1b19c71b%40googlegroups.com
>>> .
>>> For more options, visit https://groups.google.com/d/optout.
>>>
>>>
>>>
>>> --
>>> Chad Baker
>>> Professor Emeritus
>>> Electrical and Computer Engineering
>>> Christian Brothers University901-...@cbu.edu
>>>
>>>
>>>
>>> --
>>> Chad Baker
>>> Professor Emeritus
>>> Electrical and Computer Engineering
>>>
>>> --
>>> For more options, visit http://beagleboard.org/discuss
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