Hi, Thank you for you response.
I have a lot of 74xx components which may be dead. As my first project with the Beagle, I would like to simply test the logic behind these chips (monitor the logic to detect wrong values). I first planed to wire the 74LS02 like this : But you mentioned that an output high ranges from 0 to 5v which could damage Beagle GPIOs (not 5v tolerant). If someone could give me more advises please ... Thanks 2015-03-11 11:01 GMT+01:00 Eric Fort <[email protected]>: > first off, to properly answer your question we need to start by > referencing the datasheet for the part you wish to use found here: > http://www.ti.com/lit/ds/symlink/sn74s02.pdf > > something missed by many is that 3.3v OUTPUTS on a device such as the > beagle will drive standard 5v TTL logic just fine! just make sure to limit > your fan out (number of logic loads) appropriately. The reason for this > becomes clear if one actually reads the datasheet referenced above for the > part you wish to use. If you look at the 74LS02 VIHmin (the minimum > voltage which the input sees as high) it's listed as 2v. since 3v3 > 2v0 > it works fine. the problem you have is that the output of the 74LS02 > swings from 0-5v so when the output of the 74LS02 goes high it will measure > 5v. since 5v > 3v3 it will cook a 3v3 INPUT. So depending what you want > to do you may or may not need voltage translation andin most cases (i2c > buses being the major place where you find an exception and do need > bidirectional) they need only be unidirectional and one may use simpler > circuitry such as a transistor or resistance ladder/voltage divider. So > I'll end by posing a question. What doyou want to accomplish with this and > can you post a basic schematic for review for us tolookat and > constructively comment on? > > Eric > > On Tue, Mar 10, 2015 at 10:50 AM, <[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. >> > > -- > 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.
