if u want to control a servo with potentiometer
i think you do not need a microcontroller
you can use 555 timer IC in astable mode
i tried this it is working
choose the R1 and R2 resistance and capasitor values according to your servo, it works.
try in google
555ic.com(i forgot exact name)
the circuit is vary simple
refer the following BOOK
“PRACTICAL ELECTRONICS FOR INVENTORS”