Thanks @john3909. This is to avoid having external power applied to the GPIO pins of the BBB/G before is booted up which can damage the board right? I suppose that was the the problem with my fried BBG.
This should also apply with a single Tx board and a single Rx board configuration rigth? In my case the Tx sender micro (not a BBB) is powered from the VDD_3V3 pin of the BBB. I've been running for more than one month without any issue in the BBB until now. Should I also worry and use a tristate? Cheers, Jordi El divendres, 11 març de 2016 19:05:00 UTC+1, john3909 va escriure: > > 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] <javascript:>> > 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 <[email protected]> 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]. >> >> For more options, visit https://groups.google.com/d/optout. >> >> >> > >> > >> > >> >-- >> >Gerald >> > >> >[email protected] >> >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] <javascript:>. > For more options, visit 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
