Got it. Sounds like a DAMHIK situation; -) So you're saying that VDD_3V3B does not come up quickly enough to power external devices before the boot configuration is read from the pins? You'd think we should have held off boot a little longer until supplies settle. Given there's no P8/9 accessible way to prolong boot, short of driving a tiny solenoid to hold the reset button down a little longer, how might one isolate the input protection diodes until bot is safely started?
I think my answer lies in that the cape is also providing the 5V to the BBB, so I can delay that until my own 3.3V supplies stabilize. Seems a waste of the 3.3V regulator on theBB though. Perhaps manipulating the PWR_BUT (PB_IN signal on the TPS65217C PMIC) on P9 might solve this... My loadings are a single LVC gate on each line, so basically nothing there. Thanks for the advice. Do you think a delayed reset via the PWR_BUT signal would provide the answer? On Saturday, September 5, 2015 at 10:03:42 AM UTC-6, Graham wrote: > > Mike: > > In the case of those boot programming pins, the definition of "not-driven" > includes NOT LOADING the pins. > > If you are using CMOS inputs on I.C.s that are already powered up, then > O.K. > > If the the "inputs" that you are hanging on the boot pins are ICs that are > not powered up yet (because you > used the VDD_3V3B rail to power them), then the ESD diodes are putting a > short to ground on the boot pins. > > If the "inputs" that you are hanging on the boot pins are bipolar > transistors, with pull down resistors > in the circuit, you could be over-riding the boot instruction "highs" and > turning them into lows. > > You have been warned. :-) > > --- Graham > > >>> -- 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.
