On 4/27/2014 5:30 PM, Britton Kerin wrote: > Bad things happen when I try to power the beaglebone through the header pins. > I'm doing this by connecting an external 5V supply to header P9 pin 5, > and ground header P8 pin 1. > > I have the pull-downs for GPIO1_12:15 enabled in software. I believe this is > done correctly: I've verifying that the pull-downs overcome a large external > resistor pulling up, and that enabling the internal pull-up instead works > as expected (my interface doesn't support no-pull so I can't test that). > > The IO pins stay right near 0V when I power the bone through the jack. When I > power it through the the header as described above, the pins float up to > 0.1 V or more, sometimes high enough to cause spurious high reads on the pins.
How "large" is your external pull-up resistor? The AM335x pull-down current is specified to be between 51 and 210 uA, so if you see 0.1V at the pin, that would put your external pull-up at 15K to 63K. Be more specific on your exact circuit, the exact voltages you are seeing, and all details related to operating state when you measure the values. Basically, there should be zero difference between powering the BeagleBone from the DC power jack and powering it from VDD_5V on the P9 header since the two signals are tied together. -- Charles Steinkuehler [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]. For more options, visit https://groups.google.com/d/optout.
