Thank you for all your advices. There shouldn't be any problem if i use a bidirectionnal voltage shifter ?
2015-03-10 20:17 GMT+01:00 Harvey White <[email protected]>: > On Tue, 10 Mar 2015 12:02:35 -0700, you wrote: > > >You'll have to take steps to scale the voltage down to the BBB's 3.3 V > I/O level. The best way to do this is with dedicated voltage-level > translator ICs. But depending on your application, you might be able to get > away with current-limiting resistors in series from the 74xx output to the > GPIO (you'll have to do some work to find the right value), and with the > right 74xx selection, you won't need to put anything between BBB outputs > and 74xx inputs (that will depend on what the 74xx Vhi threshold is). > > It's reasonable to do that when you have a 5 volt system with a number > of lines, and can't substitute the part (a 5 volt display, for > instance). > > I would NOT use current limiting resistors, I don't thing that they > solve the problem. > > As I remember it, and they could have changed things and this is not > as much of a problem now, the way that the pin is internally > constructed involves back biased diodes which connect to the power > supply rails. These back biased diodes, if forward biased, make an > SCR, which once turned on, stays on until the power is interrupted. > > The voltage causes these SCR's to become functional, then fire. The > SCR then uses the internal power supply to provide enough energy to > destroy the I/O structure in the chip. > > Current limiting resistors do not help, because it's not the current > coming in that does the damage, it's the relative voltage level. > > This is called a "parasitic SCR" and has destroyed chips in the past. > Whether or not it is a problem still, I do not know. > > You'd want to have chips (to connect the 5 volts to) that have 5 volt > tolerant inputs. These processors do not. > > Better to use 3.3 volt logic everywhere possible, and level translate > only when talking to a 5 volt system that cannot be redesigned. > > Talking, in this case, means signals going either direction. > > > > >Or maybe you can use 3.3 V 74xx variants. > > This would be my preferred solution, yes. > > Harvey > > > > >> On Mar 10, 2015, at 10:50 , [email protected] wrote: > >> > >> Hi, > >> > >> I come from the world of sotware engineering and I am a newcomer > (nearly) to the world of electronic. I would like to know if it was > possible to interface a 74LS02 to the BeagleBone Black. > >> > >> I plan to connect Vcc and Vss of the 74LS02 to the 5V Vdd output and > Gnd of the Beagle and use the GPIO pins to command the logic inputs. My > problem is that I don't know if I can plug the 74LS02 without components > such as resistors, in order to limit the current flowing through > components. I don't want to damage the board. > >> > >> The result of all the logic operations should be gathered by some GPIO > pins configured as inputs. > >> > >> Is it possible to proceed that way ? > >> > >> Thanks in advance for your answers > >> > >> -- > >> 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. > > > > > >-- > >Rick Mann > >[email protected] > > -- > For more options, visit 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/hTzOjUNwFZE/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > 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.
