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Computer Video Display

If you view a computer as an input-processing-output machine, you can use a keyboard or removable storage device as the input, a program as the processing, but what can you use to retrieve the output? One way to acquire the output, be it text or graphics, is with a video display.


Before we go into the details of how the microprocessor gets involved with the video display, lets learn exactly how a video display works. We'll start by describing a monochrome display. If you were to examine the display with a magnifying glass, you would see that it is covered with dots. These dots are called pixels, short for "picture elements".

Letter E pixels

The picture above shows how, by turning on certain pixels, and turning off other pixels, the letter "E" can be created on the display. Early displays were a matrix 640 pixels wide and 480 pixels high.

LED matrix

A matrix of pixels can be made using LEDs (Light Emitting Diodes). A schematic for a matrix of LEDs is shown above. If ground is applied to a specific row and a positive voltage is applied to a specific column, the LED at the intersection of that row and column would light up. Using this method multiple LEDs can be turned on Simultaneously, thus creating a desired letter or graphic shape.

OLED matrix

How an OLED Works

If you were to examine a modern OLED (Organic LED) display with a magnifying glass, you would see that it is covered with red, green, and blue rectangles. An organic LED is similar to a regular LED, except the material that emits light in response to an electric current is an electroluminescent organic compound rather than a semiconductor crystal.

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