Use a tristate buffer between the BBB TX and the BBB/BBG RX. Use a 2 input AND gate with the output connected to the buffer enable and a GPIO_EN from the BBB RX board connected to on of the AND gate input and a GPIO_EN from the BBG RX board to the other AND gate input. When both BBB/BBG board are fully booted, and their RX pins configured as inputs, set the GPIO_EN pins high, so that the buffer is no longer in tristate.
Regards, John > On Mar 11, 2016, at 8:19 AM, Jordi Segura <[email protected]> wrote: > > 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 <jor...@ <>gmail.com > ><http://gmail.com/>> 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 > >> <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...@ <>googlegroups.com <http://googlegroups.com/>. > >> For more options, visit https://groups.google.com/d/optout > >> <https://groups.google.com/d/optout>. > >> > > > > > > > >-- > >Gerald > > > >ger...@ <>beagleboard.org <http://beagleboard.org/> > >http://beagleboard.org/ <http://beagleboard.org/> > > > -- > For more options, visit http://beagleboard.org/discuss > <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] > <mailto:[email protected]>. > 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. 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