gbrochard,
To summarize Wiki, to control a servo you need to generate a train of short pulses (between 1ms to 2ms long), repeating each 20ms (50Hz). When pulses length is 1ms, the servo is in 0deg position, and for 2ms pulses it rotates to 90deg position.
The pulse train can be generated by various techniques, the simplest one would be using PWM block in a Single Shot mode, triggered by a 50Hz clock. When PWM Compare register varies between 100 to 200 (using 100kHz PWM clock), the output pulse will change from 1ms to 2ms.
For more meaningful help, please provide the servo's part number.
