Thanks for answers so far. Yes my case is a single Tx output driving two Rx inputs. All processors are at 3.3 V.
My original explanation of what I did: The BBG died after several days working 24/7, powered up from a power supply 5V 2A, with an 3G usb dongle connected on it, and (maybe that's my fault ...) I connected the Tx output of another microcontroller to one Rx input of the BBG but also to one Rx input of a BBB (I had both the BBG and the BBB receiving the same Tx signal from a third micro). The same power supply was powering both systems (BBG and BBB) and I also interconnected GNDs. The third micro sending the Tx signal was powered from the BBB. BBB is working well so far. Jordi El divendres, 11 març de 2016 17:00:01 UTC+1, Harvey White va escriure: > > On Fri, 11 Mar 2016 09:29:07 -0600, you wrote: > > >I would not recommend shorting outputs of two processor together, > something > >might get fried. > > Exactly right, the output drivers will likely overheat and perhaps be > damaged when one chip is outputting a different state than the other. > > In this case, it was a single output driving two inputs. With > properly connected grounds, there shouldn't be a problem with multiply > connected outputs. > > However, the question may be one of voltages. The maximum voltage > input to the processor is 3.3 volts, and if driven by a 5.0 volt > source can certainly damage the processor. > > Paranoid design would have a buffer (running from the processor's VCC) > connected to the real world, input to the real world, output to the > processor. At the other end (driving end) you use another buffer to > drive the line, both must be either inverting or non-inverting. For > each additional input to another processor, use another buffer. > > If the processors use different supply voltages, then you would want a > circuit to translate the voltage levels. There are chips that are > designed to do that. > > I use a similar idea when connecting I2C driven systems (PCA9517 works > well). > > RS-232 drivers work the same way, and in fact, would be very tolerant > of voltage level differences. I'd suggest a MAX232 style chip. The > outputs of the chip are +/- 9 volts, so absolutely cannot be connected > directly to a processor. > > Harvey > > > > > >Gerald > > > >On Fri, Mar 11, 2016 at 9:27 AM, Jordi Segura <[email protected] > <javascript:>> wrote: > > > >> Related to my unanswered problem below, main point I want to know is: > >> > >> Is it safe to connect directly the same Tx external signal > simultaneously > >> to a couple of BBs ? > >> > >> Cheers, > >> Jordi > >> > >> El dilluns, 7 març de 2016 0:11:32 UTC+1, Jordi Segura va escriure: > >>> > >>> My BBGreen got fried (when I power it up it just dims once the power > led > >>> and that's all it does). > >>> > >>> > >>> Can someone explain me what I did wrong so it won't happen to me or > >>> others again? > >>> > >>> > >>> Explanation of what I did: The BBG died after several days working > 24/7, > >>> powered up from a power supply 5V 2A, with an 3G usb dongle connected > on > >>> it, and (maybe that's my fault ...) I connected the Tx output of > another > >>> microcontroller to one Rx input of the BBG but also to one Rx input of > a > >>> BBB (I had both the BBG and the BBB receiving the same Tx signal from > a > >>> third micro) > >>> The same power supply was powering both systems (BBG and BBB) and I > also > >>> interconnected GNDs. The third micro sending the Tx signal was powered > from > >>> the BBB. BBB is working well so far. > >>> > >>> > >>> Cheers. > >>> > >> -- > >> 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.
