Turn on what? A siren? Drive a relay? An open collector output? What would that be?
Which MCU are you using?
And what kind of interrupt? Level or edge?
Please provide some more details about project scenario, a schematic would be even better. :wink:
Sorry, I don't use pic to further help you with the code, but you don't need to make the circuit more expensive with the use of 555. PIC timers are already there, you could use them as well.i am using pic16f877a controller... i want my controller to generate a level interrupt that will go to 555timer and the siren will turn on.