Oh thanks a lot ,too many puzzeles have been solved in my mind with this answer of yours ,i m really feeling like i have jumped from beginner level to 5 steps ahead thanks again, i have an electronics desin of a ups circuit and i am only asking questions related to it ,now the next part of my question is that this pic16f72 generates an AC volt pulse at two of its pins at 50 hrtz , i want to know the command for doing this ,another thing that how can i make two output pins to opposite of one another ,for example if i take porb.0 and portb.1 , if one port is equal to 1 then other should automatically become equal to 0 and vice versa ,