How does the Lightpen work?
The Lightpen sends a negative edge pulse to “button 4” when it senses a certain intensity of light. The software on the program cartridges places a “crosshair” on the screen or monitors predetermined text menu selections. By aiming the Lightpen at this crosshair it draws a shape similar to a bullseye. As the pen is moved, it crosses the rings of the bullseye and this new position is detected and made to be the new center. In this manner the bullseye crosshair may be dragged across the screen. If it is lost by the Lightpen, it must be “picked up” again.
