how can i make a processing on a wave by using pic16f877a if it exceed a level the pic will have output_high. thank you
You need to scale down your signal and make sure it can never swing above/below Vdd/Vss. Easiest way to do this is with an a pair of op-amps (depending on the signal). First op-amp scales and/or shifts the waveform, second op-amp powered from the same supply as the PIC ensures the voltage cannot exceed the supply rails to the PIC. You could also clip high voltages with a suitably rated zener assuming 5V supply.