That should be OK. Gerald
On Tue, Feb 18, 2014 at 9:33 AM, <c...@isbd.net> wrote: > Gerald Coley <ger...@beagleboard.org> wrote: > > On Tue, Feb 18, 2014 at 8:08 AM, <c...@isbd.net> wrote: > > > > > The BBB manual says both these things about applying inputs to the I/O > > > pins:- > > > > > > NO PINS ARE TO BE DRIVEN UNTIL AFTER THE SYS_RESET LINE GOES > > > HIGH. > > > > > > Do not drive any external signals into the I/O pins until after > > > the VDD_3V3B rail is up. > > > > > > > > > So, do these actually mean basically the same thing, or if not, which > > > one is actually correct? Using the VDD_3V3B to gate external input is > > > much easier because of its greater current capability but both are > > > available on the headers so one could use either. (Or even worse, is > > > it *really* an AND requirement?) > > > > > > When the BBB is powered down will these two signals go low early > > > enough so that input signals gated by them will be removed in time? > > > > > > > SYS_RESET is the safest way to do it as it is a signal that can be used > > with enough delay to allow the 3V3B to settle. The desired requirement is > > after the 3V3B is up. But that is not a nice signal to track as it is a > > voltage rail. Easy is not always the best way. > > > OK, it makes little odds really as there will be some sort of logic > driven by either SYS_RESET or 3V3B so the current drive will be minimal. > > > > Power down is in the reverse order of power up. Once 3V3B is removed > > your circuitry should be powered down at that point. > > > So if I used a device powered by the 3V3B to drive the ADC voltage input > (obviously potted down to a maximum of 1.8 volts) would that be safe > enough? E.g. an op-amp in follower mode? > > -- > Chris Green > ยท > > -- > 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 beagleboard+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > -- 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 beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
