Understanding the PWM (Pulse Width Modulation) for a Hobby Servo

The hobby servo requires a PWM to turn the horn (shaft) of the servo. The particular hobby servo that is being used is a Hitec and this servo requires the PWM period to be at 20ms (milliseconds). The actual pulse is only 0.9ms to 2.1ms in width. That means that the pulse width of .9ms will turn the servo to one extreme and the 2.1ms will turn the servo to the other extreme (180 degrees).