Video Hardware

Objectives

In this chapter, you will:

-Learn how CRT displays operate

-Learn how LCD displays operate

-Learn how flat-panel displays operate

-Understand how to choose the right dot pitch, resolution and refresh rate

-Understand VGA and SVGA standards

-Examine the video chipsets available today

-Discuss 3D graphics accelerators

-Troubleshoot monitor and display adapter problems

Peripheral Output Devices

When the device is outside the computer’s main case, we generally call it a peripheral device.

Peripheral means on the edge or outside of an area.

Standard devices include keyboards, floppy and hard drives, monitors, mice, scanners, printers, modems, CD-ROM or DVD, and sound cards.

Peripheral Output Devices

The output device is the thing that produces what we normally would see.

Display screens are usually the standard output device and considered the most important

When we connect something to a motherboard for the purpose of input, output, or storage, we refer to that thing as a device

Transient vs. Final Output

Output relates to time, in the sense that you can have transient output and final output.Transient output is the stream of data being sent somewhere for fleeting observation of temporary storage. An example of transient output is pressing on the keyboardAnother example is when an application is holding too much information for the installed RAM, and sends part of that information to the hard disk for temporary storage. This is called a swap file. A swap file is somewhat similar to a buffer.Final output is data that moves away from the system completely and stays fixed in time.

Video Displays

Monitors have been called cathode ray tubes (CRT); Video display terminals (VDTs); Console (CON), which is the DOS device name; Or simply the screen.

The video subsystem of a PC consists of two main components:

Monitor (or video display). Can be either CRT or LCD.Video adapter (also called the video card or graphics adapter. On some low cost systems, video may be built right into the motherboard.

Video Displays

A CRT is a vacuum tube with a layer of phosphor dots at the viewing end and an electron gun at the other.

Video Displays

The gun shoots a beam of electrons at the phosphor, making the electrons glow.

When we look at the glass face of the monitor, we are seeing through the glass to the backside of the phosphor layer. We can create every color of light by using three primary colors: red, green, and blue (RGB).

However for solids, we have to use cyan (bluish), magenta (pinkish red), and yellow (CMY).

Monitors

Monitors work with light, and we use an RGB designation.

Printers work with solids, and for that, we need to use a CMY abbreviation.

CMY is also used in LCD panels.

Liquid Crystal Displays

Whereas a CRT produces a beam of light, liquid crystal technology relies on another source of light to pass through crystals.

If light can pass through the crystal, our eye can see it.

When the crystal is turned off, it won’t let light pass and we see an area of black. Each crystal can be either on or off.

Liquid Crystal Displays

LCD technology allows for a much thinner screen, which gives rise to a group of monitors called flat-panel displays.

Flat-panel technology is most often thought of as an LCD monitor, but other displays can be categorized as flat panel: LCD panels, gas-plasma, and electro-luminescent display monitors.

Liquid Crystals

A fascinating property of liquid crystals is that they exist in either a solid or a near-liquid state, depending on electrical conditions.

The crystals have a tendency to be straight in their natural state, but twist into a right angle under electrical stimulation.

This ability to pass light when they are straight, of to turn at right angles and block light, gave rise to the LCD panel.

Resolution

Scanners and monitors both define optical resolution by the number of pixels per inch.The only difference is that scanners use one CCD(charged couple device) per pixel, and the resolution is limited by the physical size of the CCD. An RBG monitor uses lighted dots, each of which is one pixel.LCD panels use a molecular crystal as a pixel device, and gas-plasma screens use a pinpoint flash of heated gas to describe a pixel.

Resolution

The Super Video Graphics Array (SVGA) standard of today’s monitors is typically 1280 X 1024 or 1600 X 1200.A standard VGA monitor has 640 pixels in a horizontal axis (line) and 480 pixels vertically. 640 X 480Different graphics modes can also have varying numbers of colors, a third number refers to the number of colors associated with pixel resolution.Putting the three numbers together for HHH x VVV x CCC

Non-interlaced and Interlaced

Both modes take the same amount of time. However, given the same refresh rate, interlaced mode provides a more stable image and less flicker to the human eye.

The problem is that manufactures slow the refresh rate in interlaced monitors, and this slower rate allows for cheaper manufacturing and therefore cheaper monitors.

The ideal would be to have an interlaced monitor with the same refresh rate as a non-interlaced.

Non-interlaced and Interlaced

When the electron beam sweeps across the pixels from top to bottom and left to right, all in one pass, we call it the non-interlaced mode.This involves sweeping past every pixel triad, one after the other, covering the entire screen once then beginning again.Interlaced mode means that the beam sweeps form top to bottom in two passes.First it refreshes the odd lines, and them the even lines, like weaving, or lacing shoes half a side at a time.Every other row of pixels is glowing, and each row in between is black.

Pixel Resolution

A pixel is a fancy name for a dot.A pixel is a loosely defined as a picture element.Depending on how closely pixels can be bunched together per inch, we can say that a monitor has a resolution measurement.Resolution can be defined as “the degree of detail visible on a monitor, and therefore it is related to the size of the electron beams, the degree of focus in their alignment, the arrangement of the pixel triads, and the video bandwidth.”

Scan Cycle and Refresh Rate

Because the electron gun is a kind of mechanical device, it can blast electrons onto only one triad at a time.

It takes a certain amount of time for the beam to sweep from the top left to the bottom right of the screen. This time is one scan cycle.

The video card tells the monitor how to time the scan cycle by sending a scan frequency to the monitor.

Scan Cycle and Refresh Rate

When the beam of electrons reaches the lowest-right set of dots, it starts over again at the top left. The entire cycle, from tip to bottom than back to top, is called the refresh rate.

The faster the electrons can refresh the phosphors, the faster the refresh rate is and the less flicker the human eye perceives. For minimum flicker, the refresh rate should be at least 70 times per second (70Hz)

Standard VGA

Following the Color Graphics Adapter (CGA) and Enhanced Graphics Adapter (EGA), a new technology was developed called Video Graphics Array (VGA). VGA was developed by IBM to provide higher pixel resolution and graphics capabilities.

Safe mode in windows has a resolution of 640 X 480 X 16.

Frame Buffers

Any image being sent to a monitor begins as a series of instructions programmed into an application.

An image on the monitor takes up the whole screen, and every part of it is placed on the screen in a specific location.

The term frame applies to the single picture being shown on a monitor at any given time. As the specifics of the picture move some areas stay the same. An example would be the task bar on the Windows desktop.

Frame Buffers

The CPU keeps an area of memory – a buffer- where it stores the information being displayed on a screen at any given time.

When it’s ready, the CPU lets data out of the buffer.

The keyboard has a buffer that allows you to press keys faster than the system can process the presses. For example if you hold down a key on the keyboard, you will eventually fill the buffer, at which time the CPU will send an alert tone to the PC’s speaker.

Frame Buffers

Likewise, the video system uses a buffer for image data, and the whole amount of data that goes to the screen is called the frame buffer.

SVGA and high resolution monitors take advantage of video RAM and include a more complex set of graphic instructions than a VGA does. These instructions, working together outside of main memory, allow for faster data transfers between the CPU and the screen.

Screen Size

After resolution, the next most popular way of differentiating monitors is by screen size.

Monitors have borrowed from the television industry by measuring screen size diagonally.

Any monitor larger than 16 inches is called a full-page monitor because it can display a full page in a one-to-one ratio.

Screen Size

A monitor that is wider than it is tall is called a landscape monitor and can usually display two pages side by side.

A monitor that is taller than it is wide is called a portrait monitor.

Image Size

The actual area used to display the image is called the raster.The raster varies according to the resolution of the monitor and the internal physics of the screen.VGA at 640 X 480 on a 15 inch screen displays differently than SVGA at 1024 X 768.Television monitors usually over scan the image, putting the actually edge out beyond the raster edge, PC monitor images are designed to be smaller than the physical edges.

Screen Resolution Settings1024 X 768

800 X 600 640 X 480

Image Size

If a true black border appears around the image, then either the monitor is failing, or the image controls need to be adjusted.If the resolution of the monitor is changed from lower to higher, it can shrink all the images on the screen.On an LCD panel, an image resolution change could potentially cause a black band to appear around the edge of the panel. Because the display is designed to match the number of pixels in an image, the LCD process turns crystals on and off, based on usage.

Color Triads

In a CRT monitor, an electron gun shoots a stream of electrons at a wall of phosphorous chemicals.Phosphors happen to glow for a short time after being struck by an electron beam; however, the glow quickly fades away.The electron beam must continually restrike the chemicals to refresh the level of light.

When three different phosphors are arranged

in a triangle of dots, they become a triad.

Color Triads

The video card can manipulate the electrons to change how each dot glows.By combining red, blue, and green glowing light, we can fool the eye into thinking that it sees all sorts of colors in between.One triad in an RGB monitor makes up one pixel.Dot pitch is the diagonal measurement between the center of each pixel triad, measured in millimeters. Generally the smaller the dot pitch, the sharper the images, though a very small dot pitch can result in a loss of brightness and contrast.

LCD Panel Construction

An LCD panel is made of two polarized planes of glass placed at right angle to each other. Sandwiched between the panes of glass is a layer of liquid crystals.

Behind the back panel is a fluorescent light source that tries to get through the two misaligned panels of glass.

In the default state, the light is blocked, and the panel appears black.

Color and Light

Liquid crystals were developed that could cut out all colors of light except one. Using the cyan, magenta, yellow process, the number of crystals in the matrix was tripled.

Triads of three crystals were put together in the matrix, and the switches were tripled to access each sub-crystal. By turning on the three crystals in each triad on or off, the same effect was produced with an electron beam and phosphor triads.

Passive Matrix and Active Matrix

LCD panels have a matrix of wires. VGA resolution is 640 x 480 pixels in a matrix. Therefore, a VGA liquid crystal display panel requires 640 transistor switches along the sides and 480 long the top and bottom to produce 640 x480 dots of light.

The rows are activated sequentially, moving from top to bottom, resulting in a refresh rate and limited contrast.

Some LCD panels divide the screen into a top half and a bottom half, allowing simultaneous refresh of two rows, one in each half, similar to interlacing.

Passive Matrix and Active Matrix

The response time of LCD panels is slow. It takes from 40 to 200 milliseconds to move the crystal through it s twist and relax cycle.

The fundamental difference between passive and active matrix is the number of switches. Passive matrix has only one switch per column, whereas active matrix has at least three times that many.

Additionally, an active matrix panel gives every liquid crystal its own switch address.

Passive Matrix and Active Matrix

This allows each crystal to be turned on and off more quickly and provides better control over how long a crystal stays on in relation to its neighboring crystals.

Individual addressing also provides better control over each crystal in a triad as a grid point. Active matrix LCD panels are basically huge integrated circuits.

Video Display Adapters

A video adapter provides the interface between your computer and monitor and transmits the signals that appear as images on the display. The following is a list of old and new adapters:

MDA (monochrome display adapter) HGC (Hercules graphics card) CGA (color graphics adapter) EGA (enhanced graphics adapter) VGA (video graphics array) SVGA (super VGA) XGA (extended graphics array) UVGA (ultra VGA)

Video Graphics Array

The VGA BIOS (basic input/output system) is the control software residing in the system ROM for controlling VGA circuits.

With the BIOS, software can initiate commands and functions without having to manipulate the VGA directly.

Programs become somewhat hardware independent and can call a consistent set of commands and functions built into the system's ROM-control software.

Video Graphics Array

A standard VGA card displays up to 256 colors onscreen, from a palette of 262,144 (256KB) colors; when used in the 640[ts]480 graphics or 720[ts]400 text mode, 16 colors at a time can be displayed.

Because the VGA outputs an analog signal, you must have a monitor that accepts an analog input.

IBM introduced higher-resolution versions of VGA called XGA and XGA-2 in the early 1990s, but most of the development of VGA standards has come from the third-party video card industry and its trade group, the Video Electronic Standards Association (VESA).

Super VGA

When IBM's XGA and 8514/A video cards were introduced, competing manufacturers chose not to attempt to clone these incremental improvements on their VGA products.

Instead, they began producing lower-cost adapters that offered even higher resolutions. These video cards fall into a category loosely known as Super VGA (SVGA).

Video Adapter Components

All video display adapters contain certain basic components, such as the following:

Video BIOSVideo processorVideo memoryDigital-to-analog converter (DAC)Bus connectorVideo driver

Integrated Video/Motherboard Chipsets

Many low-cost systems, especially those using the semi-proprietary LPX motherboard form factor, have incorporated standard VGA-type video circuits on the motherboard.

The performance and features of the built-in video differed only slightly from add-on cards using the same or similar chipsets, and in most cases the built-in video could be replaced by adding a video card.

Some motherboard-based video also had provisions for memory upgrades.

3D Graphics Accelerators

The latest trend in PC graphic-display technology is the expanded use of 3D full-motion graphics in game playing. The combination of higher screen resolutions, 24-bit or 32-bit color, and dedicated 3D graphics processors has led to games that provide incredibly realistic detail. A more processor-intensive, and much more effective type of fill, is called texture mapping.