I just took a look at Rev C schematics and there is a 100K pulldown on the RX pin so I wouldn’t have expected pulling directly to ground to make it any worse. All in all 100K is not much of a pull down, but I do agree that pull up is what you want - that at least is idle state on a serial line (from what I recall). My gut feel would be to use around a 3K resistor would should allow plenty headroom for hooking up a serial monitor if you ever wanted to - its a real pity that there is no convenient 3V3 on the monitor header.
~C > On Aug 13, 2015, at 6:25 PM, AQG Chris <cwal...@gmail.com> wrote: > > I'll chime in again too - we originally tested our 3v3-rx jumper with a > direct connection, but then decided it might be nice to keep the ability to > use the serial debug port. Right now we've got a 470 ohm resistor pulling rx > up, which seems to allow communication over serial still. We also tried > values of 220 through 1kohm and were still able to send characters to uart0. > 100 ohm was too low to send anything over serial. I've not done extensive > reboot testing yet with each of these, but we will likely settle on either > 470 or 1kohm. > > If you probe the RX pin of the BB with nothing attached, we find 0v. The TX > pin (both on the BB and on the FTDI board we attach to the BB) is at 3.3v by > default, and we've also noticed that the problem never occurs when we're > hooked up to uart0 with our FTDI chip adapter. That made pulling the line up > rather than down an attractive option. We did try pulling RX down to ground > at some point, but the very first test I did after that resulted in power LED > on but no boot. > > We still haven't done a mass deployment, so for now I'm taking our smaller > testing runs and experiences like Ivan's to guide us. Sidenote - yes, we > have noticed eth0 not showing up as well, although it's not critical for our > application. > > On Thursday, August 13, 2015 at 4:04:34 PM UTC-7, Colin Bester wrote: > In my case I am running 3.8.13-bone68 and system is pretty darn solid if it > does start up. I have not seen Ethernet fail nor have I had any random > reboots, but occasional I do have a device not power up when power is > applied. We have not been able to determine a consistent cause and I am not > convinced it's due to the mentioned RX pin as I am pretty sure I saw that > this pin is pulled low (which I still think is wrong polarity) on rev C > boards. > > In addition, we have physically blocked off the PWR button and only expose > the reset button via a small pin hole in our enclosure. > > > > On Thursday, August 13, 2015 at 5:42:23 PM UTC-5, ivan.wu...@gmail.com <> > wrote: > Hi Robert, > > > Please confirm which kernel your running > > 3.8.13-bone71 (updated beginning of last June) > > > There's a big thread on this list, where a bunch spend about 2 weeks > > bisecting the v4.1.x kernel to find the cause of the "random" reboot.. > > I don't have an issue though with random reboots - the reboots are initiated > on purpose by my application (because of the eth0 problem) - but as described > 2 in 30,000 reboots failed. > > Cheers, > Ivan > > > -- > For more options, visit http://beagleboard.org/discuss > <http://beagleboard.org/discuss> > --- > You received this message because you are subscribed to a topic in the Google > Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/aXv6An1xfqI/unsubscribe > <https://groups.google.com/d/topic/beagleboard/aXv6An1xfqI/unsubscribe>. > To unsubscribe from this group and all its topics, send an email to > beagleboard+unsubscr...@googlegroups.com > <mailto:beagleboard+unsubscr...@googlegroups.com>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- 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/d/optout.
