PPK external trigger

Question

Hello: 
 I tried to find this in the documentation but could not. Regarding the external trigger to the PPK (TRIG IN pin). Does this require a high-to-low transition, a low-to-high transition, or a pulse? If it requires a pulse, what is the minimum pulse width? 
 Thanks!

wlgrd · Accepted Answer

It depends on which revision of the board you have. 
 Version 1.1.0 needs a transition from low to high, and is pulled to GND when not held high externally. 
 Versions below 1.1.0 was missing this pull-down, and thus need the same transition, but also to be externally forced to low in between triggers. 
 With regards to timing, I don't know for sure, but it shouldn't cause any trouble. The GPIOTE module that reads this transition runs on a 16MHz clock. So it needs more than 62.5ns. But, we also have a pad capacitance of 3pF, which plays a role on how fast you can get up to the required voltage to accept it as a transition (which is minimum 0.7*VDD).