The controller can accept commands on the UART and to make the required number of steps in the right direction. The direction of rotation and the required number of steps given by a single command. For example, to make the 300 steps to one side sends a command 300. If you want to rotate in the opposite direction, sending "-"and the number of steps, it's simple. Also provides for rotation of the engine buttons.
to view go here http://www.youtube.com/watch?v=ceC7vqkssWo and http://www.youtube.com/watch?v=JTbJFN6Hsy4&feature=channel_video_title
more information http://avrproject.ru/
buttons and pins