@Guy I have been away for a bit thus my late reaction. Can you give me a hint how to change the pullup to pulldown at bootup?
Op maandag 21 april 2014 21:02:52 UTC+2 schreef Guy Grotke: > > I would not fight the enabled pullup with my own pulldown: Either change > your control program and circuit to take high as inactive, or change the > boot software to program that GPIO with no pull resistor (so you can add > your own external pulldown) or program that GPIO with the internal > pulldown > enabled. > > Fighting the internal pullup with a higher-current pulldown is just asking > for trouble. > > -----Original Message----- > From: [email protected] <javascript:> > Sent: Friday, April 18, 2014 12:11 PM > To: [email protected] <javascript:> > Subject: [beagleboard] Re: Change default state of GPIO pin > > If there is a pullup then your pulldown will have to be several times > stronger to make sure that the floating value becomes a logic low. You now > have an effective voltage divider with a pullup / pulldown configuration. > Fighting against the configured on-chip pullup is going to mean that to > output a high you're going to need many times the drive current you would > normally need as you sink current into that low-value pulldown resistor. > > Not sure what your threshold on the buzzer is but if the pullup is say 30 > to > 50K then to get a solid 10% default low on the pin you'd need a 3 to 5K > resistor on the pulldown. That would be a 1.1 to 0.6mA load on the pin > when it swings high. You're also burning 0.1mA when the pin floats since > the voltage divider will always be present. That may or may not impact > your design. > > Assuming I'm thinking of this correctly. > > -- > 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] <javascript:>. > 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]. For more options, visit https://groups.google.com/d/optout.
