Light Pen - input and output devices

It is a pointing device. This has a light sensitive tip that is excited while the light is emitted and an illuminated point upon the display comes in its field of view. Different type of devices that have connected hardware to track the device and find out x and y values, the light pen requires software support as several kind of tracking program. Pointing operations are simply programmed for light pens.

Figure: Light Pen Application

Figure in above shows two typical applications of a light pen. This has a light sensitive tip and also a photocell mounted in a pen-like case. Whether the light pen is pointed at an object on the screen this generates information from that the item can be identified through the program.

While the light pen senses an illuminated phosphor, this interrupts the display interpreting the processors of the file display. The instruction register of processor tells that instruction in the display file was being executed. Through identifying the instruction liable for the illuminated point that the machine can discover that object the pen is pointing to.

A light-pen is an event driven device. The processor that has to wait until it comes across an illuminated point on the display to acquire any information. The keyboard is the other typical illustration of an event driven device. Such processor has to wait for a key to be pressed before this can find out what the user needs to input.