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 On Fri, May 13, 2016 at 12:21 PM, William Hermans <[email protected]> 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. > > On Fri, May 13, 2016 at 10:19 AM, William Hermans <[email protected]> > wrote: > >> *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. >> >> On Fri, May 13, 2016 at 9:14 AM, Chad Baker <[email protected]> wrote: >> >>> 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"; >>> <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 >>> >>> >>> On 5/13/16 10:48 AM, [email protected] wrote: >>> >>> 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! >>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "BeagleBoard" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To view this discussion on the web visit >>> <https://groups.google.com/d/msgid/beagleboard/81b4dd20-bdad-4034-b024-d71f1b19c71b%40googlegroups.com?utm_medium=email&utm_source=footer> >>> 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 [email protected] >>> >>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "BeagleBoard" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/beagleboard/5735FD57.7070009%40cbu.edu >>> <https://groups.google.com/d/msgid/beagleboard/5735FD57.7070009%40cbu.edu?utm_medium=email&utm_source=footer> >>> . >>> >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/beagleboard/CALHSORpLNKC0ch2GEoXDnrOb7dtuF37PQHOGUKw9cQgFoP%2B-5w%40mail.gmail.com > <https://groups.google.com/d/msgid/beagleboard/CALHSORpLNKC0ch2GEoXDnrOb7dtuF37PQHOGUKw9cQgFoP%2B-5w%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- Gerald [email protected] http://beagleboard.org/ [email protected] -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/CAHK_S%2Bepwg4uepCevMAjy_5BvxBSyAj3uiYquoHkDuu-8u5v8g%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
