Quote Originally Posted by Melanie View Post
The reality is that a PIC I/O's can be indeterminate on Power-On. Set the I/O's as one of the first things you do when you Power-On your PIC. Leaving them set to input (high impedance) may be enough to trip your circuitry.
Hello,

Thank you for the answer.

About the pins status at power on, I read in the datashet that it is in undetermined state, as you say. I set PORTA in the program but it seems to be too late because the NE555 already got a logic HIGH from the pin by the time the PORTC register is written.

What is "tripping" a circuitry? (sorry if I sound ignorant).