How do I ask the designer? On Wednesday, February 19, 2014 8:43:05 AM UTC-5, Gerald wrote: > > Did you ask the designer? > > Gerald > > > > On Wed, Feb 19, 2014 at 7:33 AM, <[email protected] <javascript:>>wrote: > >> I was having flaky USB behavior on multiple BBB boards and so >> investigated the USB Power control circuitry. Her is what I found. >> >> The Pull-Up resistor on the USB1_OCn signal has an invalid voltage >> reading. The pull up should set the signal at 3.3V as the resistor is >> attached to a 3.3V supply. (this was verified through measurement). The >> value of the pull up is 10K as shown. >> Essentially what I see is that during certain USB activity the main >> processor will disable the USB1_DRVVBUS signal which turns off USB power. >> My theory is that the voltage level on the USB1_OCn signal is close to the >> value which would indicate an Over Current condition. >> The processor then removes power and disable the USB bus. (this is my >> theory but I am not positive on this) >> >> What is a fact is that the voltage on the USB1_OCn signal is at an >> improper logic value for a 3.3 Volt IO signal. The processor will at times >> remove the USB1_DRVVBUS signal hence removing USB power. >> >> I have watched the USB1_OCn signal while the processor removes the >> USB1_DRVVBUS signal. It does not change value to 0 volts as would be >> expected when a true over current condition occurs. I also forced the Over >> Current condition by grounding the USB1_OCn signal to verify that the >> processor will remove the USB_DRVVBUS signal when a truen OC event occurs. >> It did remove the USB_DRVVBUS signal as expected. >> >> To investigate why the USB1_OCn signal was being held in an improper >> state, I lifted Pin 5 of U8 removing the open drain driver. The voltage >> remained at the incorrect logic level showing that the culprit is not U8. >> >> I tried to come up with a work around by lifting pin 4 of U8 and pulling >> it high such that the processor could not remove the power from the USB >> port. In this case the kernal will not recognize the USB port. During >> boot, the USB_DRVVBUS signal never goes to a high state. I monitored this >> signal even though it was not attached to U8. I believe the USB Bus >> voltage is present at the main processor before the main processor wanted >> it be there and during boot gets upset and does not enable the port. >> >> So.... >> >> Can anyone from Beagle explain why the voltage on R52 is sitting at 2.4 >> volts? >> >> -- >> 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/groups/opt_out. >> > >
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