Need help setting up my ultrasonic distance sensor

[Megahertz]

Hi, I just bought my Ultrasonic distance sensor (Datasheet attached).
I would like some help, may be few lines of code to give me a starting point for how to set it up for my purpose which is to sense the trigger pin going low when distance is less than 3 meters. I will be using 16F877A with this distance sensor which can take care of few other jobs as well.
I would also like to know how I can do the similar thing i.e. take readings of PWM output and measuring the pulse to know the distance. Again few lines of code in Pickbasicish will be better than instructions in plain english. Thanks