Frederic: If you look at the diagrams in the System Reference Manual, the BBB uses 100K Ohm pull up and pull down resistors to tell the processor how to boot. So any load low enough to cause a line with 100K Ohm pull up or pull down to change logic state will cause boot problems. I would estimate that any load, less than 200 K Ohms can cause this problem, even though it is an "Input". Also, inputs connected to unpowered ICs will clamp a line to ground, because of the ESD diodes in the IC.
So, either use powered buffer ICs that have only a CMOS input load, or a transmission gate as you described. I think you can switch the transmission gate using the 3.3V rail coming out of the BBB, since it does not come up until the unit is finished booting. Do not put an unpowered transmission gate on the GPIO lines, because of the ESD clamping I described. --- Graham == On Tuesday, August 11, 2015 at 2:04:59 AM UTC-5, Frédéric wrote: > > Hi! > > I'm testing my 32 channels servos cape, and I found a bad issue: when I > plug the servos, the BBB does not boot anymore. > > The problem comes from the fact I'm using some pins which are also used by > the system to determine the boot sequence. > > What I don't understand is that a servo in an input, and I though it would > not cause any problem. But the input load is maybe too low? Any idea how I > could solve this? Using a buffer with a tri-state mode, driven by the > SYSRESET pin ? > > Thanks, > > Frédéric > -- 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.
