Serial Servo Controller using Basic Stamp
Servos' positions are determined by a pulse width signal with a repetition rate of typically 50Hz, so one pulse every 20ms.  



The servo's neutral position (halfway) agrees with a 1.5ms pulse width. Shorter pulses will rotate the servo to the left, longer pulses to the right. So all you have to do is periodically create pulses. This document has a servo control demo on page 146. The code used in this demo is simply  

PULSOUT Servo, (pWidth */ PwAdj)  ' move the servo
PAUSE 20                          ' servo refresh delay