This does beg one last question - as I am using expansion connector pins to provide chip selects for numerous peripherals, what is the default state of the AM335X pins at powerup, until the boot configuration is loaded? I've slogged through the TRM as best I could, but want to make sure we're not inadvertently enabling multiple chip selects that may drive competing, say, SDOs (peripheral) into SDI (cpu) before the boot configuration is loaded.
Ideally, they would be defaulted as inputs or tri-stated outputs, in which case a weak pulldown on the peripheral CSn lines should keep things quiet. Despite my best efforts at searching the 4K+ pages of the TRM, I have not found a clear answer as to the pre-boot load default pin configuration. I probably missed it, but my search-fu fails me. Mike On Monday, September 7, 2015 at 8:22:04 AM UTC-6, Gerald wrote: > > That would be nice as well. But that is your call. > > Gerald > > On Sun, Sep 6, 2015 at 8:46 PM, rattus <[email protected] <javascript:>> > wrote: > >> You may have seen I mentioned that no signals would be driven onto the >> BBB expansion headers until enabled to do so (if I forgot to mention that, >> they won't be); all other pins are inputs to the expansion card and thanks >> to Graham's advice will be powered first to ensure protection diodes will >> not interfere with the boot configuration. >> >> Mike >> >> On Saturday, September 5, 2015 at 7:10:43 PM UTC-6, Gerald wrote: >>> >>> Well, I think there is a better way that relying on luck. I suggest you >>> take a look at >>> http://www.elinux.org/Beagleboard:BeagleBoneBlack#Expansion_Header_Pin_Usage >>> >>> Gerald >>> >>> On Sat, Sep 5, 2015 at 7:51 PM, rattus <[email protected]> wrote: >>> >>>> I went with a little LDO to provide a local 3.3V source; looks like >>>> it'll pop up in about 50-100uS after 5V is available. >>>> >>>> Thanks again. >>>> >>>> >>>> On Saturday, September 5, 2015 at 12:22:21 PM UTC-6, Graham wrote: >>>>> >>>>> I think the VDD_3V3B rail is deliberately held off until the unit has >>>>> started booting, >>>>> and has already read the boot instructions. It is not a rise time >>>>> issue. >>>>> I suspect it was done deliberately to help with the "don't drive the >>>>> rest of the pins" issue. >>>>> >>>>> A little 5V to 3.3V regulator to power your LVC "input" IC will work >>>>> nicely. >>>>> Provided that it is powered at the same time the BBB is. >>>>> That is, use VDD_5V if powered from the power jack. >>>>> >>>>> Relative to power appearing at the power jack: >>>>> SYS_5V is delayed 50 ms. >>>>> VDD_3V3B is delayed 100 ms. >>>>> SYS_RESETn is delayed ~130 ms. >>>>> >>>>> I have not measured power supply sequencing when powered by USB. >>>>> >>>>> Or if you are dealing with both I and O on the boot pins, use >>>>> something like >>>>> a 74CBTLV3126 bus switch / transmission gate to isolate your circuitry >>>>> from the BBB while it is booting. Just make sure the bus-switch / >>>>> transmission-gate >>>>> is powered while the BBB is booting. >>>>> >>>>> This issue only comes up about once a week here on the forum. :-) >>>>> >>>>> --- 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. >>>> >>> >>> >>> >>> -- >>> Gerald >>> >>> [email protected] >>> http://beagleboard.org/ >>> >> -- >> 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. >> > > > > -- > Gerald > > [email protected] <javascript:> > http://beagleboard.org/ > -- 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.
