Quote Originally Posted by mister_e View Post
How neat the signal on PORTA.5 is? Where this signal come from?
Looking at the signal in question on an o-scope, It looks pretty clean to me. It is connected to a 100K pull-up to 5V. The transition from high to low does have some ringing , that lasts about 90nS give or take, but the peaks are all < 0, so it should still be seen as a low.