This is a little very simple code to produce the required servo pulse by reading an analog port (say a pot).

It then creates the pulse after some maths and loops back again.

Code:
again:
adcin channel,value          'read pot value
if value>250 then value=250  'compress value over 250
pulse=4*value+1000           'upscale from 1000 to 2000
HIGH output_pin
pauseus pulse     'create the servo pulse
low output_pin
pauseus (20000-pulse)' pause for the rest of the 20ms period
goto again
Ioannis