I was attempting to emulate the PRU cape, which uses P8_44 as a PRU output.
However, the PRU cape uses a FET switch, gate connected to P8_44. It does not load the pin during boot. I used a BJT with resistor in series with the base, which was enough to disable the board! I've changed the series base resistor to 47Kohm and now it works. However, I suspect it might be a bit marginal. So I need to get some FETs! Too bad, I've got a lot of 2N2222s, they will have to be put to work elsewhere. Greg On Monday, April 18, 2016 at 8:24:41 PM UTC-4, Chris Morgan wrote: > > On Mon, Apr 18, 2016 at 8:12 PM, Greg <[email protected] <javascript:>> > wrote: > > I'm trouble shooting a problem on a simple cape for a BeagleBone Black. > > > > I have a bipolar switch for an LED, very similar to that used for the > "User > > LEDS". > > So I have added an approximately 10Kohm load to one of the "boot pins", > > which > > in header lingo is P8_44. > > > > P8_44 is also one of the "boot" pins. I'm interesting in using the PRU > > connection mode of this pin. > > > > The System Reference Manuals says the boot pins must not be driven prior > to > > coming out of reset (SYS_RESET goes high). > > > > So maybe my understanding of the term "driven" in this context is > incorrect, > > and it could also be interpreted as "loading", > > as in excessive resistive loading? > > > > I tried an experiment on both BBB and BBG with a 10kohm resistor to > ground > > on P8_44. Both refused to boot up and run. > > So is it a requirement to keep resistive loads off this pin during the > boot > > process? > > > > Regards, > > Greg > > > > Yes. > > You should avoid applying any voltage to any pin before SYS_RESET goes > high, or you'll likely permanently break something. In your case it > looks like you are changing the boot pin configuration (maybe it > defaults to an internal weak pullup?) and preventing your system from > booting. If that isn't what you intended you'll want to avoid loading > the pin until after SYS_RESET goes high. > > What are you trying to accomplish with your cape and that io pin? > There are approaches that may let you both use the pin and avoiid > changing the boot strapping but it would really help to see the > circuit you are trying to use with that pin. > > Chris > -- 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]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/3f3b9860-f48a-49dd-989d-ba272f3f1f31%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
