he said he wants to test ttl ics. I would get a low cost TTL chip tester off of ebay. cheaper then replacing a few BBB boards
On 3/12/2015 2:28 AM, Stephan Mulacz wrote: > Hello, > > What I'm missing is if the 74LS02 is a fixed requirement, or if there > is an option to use the 3.3V sibling. Thus shifting the problem to the > xx74xx02 inputs. Because if you kill the 74LS02 with your experiments > it might hurt less than if you kill the BBB. > > I would NOT use current limiting resistors, I don't thing that they > solve the problem. > > This has been done for decades. I don't see why it should not work > for the Sitara. > If the I/O voltage is 3.3V and we assume the clamping voltage 0.3V the > overvoltage is 5V-3.6V = 1.4V. As an indication of clamping diode > capability can we take the pin current capability. Eg. 4mA (varies > over pins). Than we would only need a 350Ohm series resistor. -> Take > 10k and you cover all the wrong assumptions ;-). > You can take even higher resistors (eg. 100k). But you will limit your > maximum frequency because somewhere you will not charge the capacity > of the Sitara input buffers fast enough. High resistors values can > also increase EMC susceptibility. > > Further more pins USB0_VBUS and USB1_VBUS should withstand 5V. But I > assume you need USB and you need 4 inputs. > > Chilli > > > -- > 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] > <mailto:[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.
