Hi,
The logic of the Due is of course is 3V3. I tried to run a NEXTION display (which has 5V) connected to the Due, and it works perfect. No my question: are the UARTS maybe 5V tolerant, or did i have just luck and it could happen that the SAM-Chip gets burned? (I couldn't find a notice about 5V tolerance in the datasheet of the chip)
I tried to run a NEXTION display
How did you power that display, with 5V or with 3.3V?
In general all pins of Due are not 5V tolerant, and you will kill at least the pins you apply 5V to.
The display is powerd with 5V. Not only the backlight, also the UART should have 5V. I measured onla 3.5V with my Multimeter, but i am not sure hoe quick the Multimeter is- there may be peaks of 5V. So you would agree that i was just luck so far?
More or less, yes, luck. Or, the Due is pulling the level down (this draws current which is what leads to catastrophic failure). Sometimes if the source impedance of the other end is really high you might be OK because the 3v3 side will then pull the level down and everything will work so long as the other side is OK with the signals coming back to it being 3.3v as well. But, in general you should not do this at all. If the voltage levels don't match then use level shifters. If you need slow speeds you can use resistor networks and transistors to do level shifting. If speed is important then use logic gates. A 2 input AND gate is a good choice. Both inputs go to your signal then you power the gate with the proper voltage for the receiving side. This conditions the signal with very low skew.
Thank You, AdderD, for your explanation.
Luckily i found out, that the NEXTION Hmi is only powered 5V, but has also a 3V3 chip on board and the Voltage is reduced for the logic (only backlight is 5V), so everything is Ok:-)