PREKSHA KASATWARDEEP PATELTIMOTHY ADAMS(SECTION 2.4.2)

COMPUTER SYSTEM ARCHITECTUREASSIGNMENT 1(TERMINALS)

TERMINALS

Few types of I/O devices which are discussed below as-

1. Keyboards.

2. Touch Screens.

3. Flat Panel Displays.

4. Video RAM.

KEYBOARD

Varieties of keyboards.1. Original IBM PC keyboard had a snap-action switch that made click when key is depressed.

2. Cheaper ones had a mechanical contact when depressed.

3. Better ones had a sheet of elastometric material between keys and underlined printed circuit.

4. Few keyboards have magnet under each key which passes through the coil, when pressed.

PERSONAL COMPUTER KEYBOARDS

1. Pressing a key creates interrupt in keyboard, starting a keyboard interrupt handler.

2. Handler reads a hardware register inside keyboard to get number of keys(1 to 102).

3. Releasing a key, caused second interrupt.

4. If user press SHIFT key and then press M, it means the user needs uppercase M not lowercase m.

5. Handling multikeys, Shift, Ctrl and Alt is done in software.

Touch Screen1.The first finger driven touch screen was developed by E.A. Johnson in 1965 at the Royal Radar Establishment in Malvern, United Kingdom.2.Johnson originally described his work in an article entitled "Touch display—a novel input/output device for computers" published in Electronics Letters.

3.In 1982, the first human-controlled multi-touch device was developed at the University of Toronto by Nimish Mehta. This is implemented in Iphone as pinching functionality.

Categories of Touch Screen

1. Touch devices are divided into two categories: opaque and transparent.

2. Example of opaque touch device is the touchpad on a notebook computer.

3. Example of transparent touch device is screen of smartphones, tablets, etc.

4. Basically transparent touch devices are called Touch Screens.

Types of Touch Screens Technologies1. Infrared

2. Resistive

3. Capacitive

4. Surface Acoustic Wave(SAW)

Infrared Touch Screen Technology

1. Infrared touch screen technology uses infrared transmitters and receivers to create an invisible grid of light beams across the screen.

2. When any objects like finger, stylus or any opaque objects interrupts the invisible light beam the corresponding detector senses the drop in signal.

3. This sensors are able to compute (x , y) co-ordinates of the touch point of finger or stylus.

4.Infrared Touch Screen Technology is widely used in kiosks.

Infrared Touch Screen Technology(contd.)

Advantages

1. Can be used with gloved or wet hands

2. Last long and are durable because there is no need to apply pressure

3. Scales with perimeter and not area

4. Have high clarity as there is no requirement for multiple layers or patterning on the screen

Infrared Touch Screen Technology(contd.)

Disadvantages

1. Multi-touch accuracy suffers as the IR beam pattern is spaced out.

2. Can deliver false responses if the user’s finger hovers before touching the screen.

3. Cannot distinguish between user input or foreign objects like mud or insects crawling on the screen.

Resistive Touch Screen Technology1. Resistive touch screens are made up of two layers, the top one of which is flexible. It contains large number of horizontal wires. The layer under it contains vertical wires.

2. This both layers are separated by air gap in an ideal condition.

3. When pressure is applied by user by finger or stylus on screen, one or more wires from upper layer comes in contact with its perpendicular wires in lower layer.

4. This connection of wire causes a current flow which is sensed by sensors and points it out to device.

5. Example: ATM machines.

Resistive Touch Screen Technology(contd.)

Advantages:

1. Inexpensive to make.

2. Can accept an input from anything, including pens, gloved fingers etc.

3. Can be easily assembled from the component parts; screens and sensors.

4. Can work in rain or in the presence of other fluids.

Resistive Touch Screen Technology(contd.)

Disadvantages:

1. Does not support true multi touch.

2. Is not very sensitive and excessive force is needed for touch activation

3. Distortion in electric field between layers can cause errors in touch detection

4. Outer layer scratches easily resulting in dead zones.

Capacitive Touch Screen Technology1. Projected Capacitive touch screen enables user to use multiple fingers at the same time which is required for pinching and expanding gestures.

2. All touch screens that can detect two or more points of contact at the same time are known as multi-touch screens.

3. In such type of touch screen grid like pattern is formed by vertical thin wires and horizontal wires which are separated by a thin insulator.

4. When a finger touches the screen it changes capacitance at all intersections.

5.This change can be measured.

Capacitive Touch Screen Technology(contd.)

1. In operation, voltages are applied alternately to the horizontal and vertical wires while the voltage values, which are affected by the capacitance of each intersection, are read off the other ones.

2. This operation is repeated many times per second with the coordinates touched fed to the device driver as a stream of (x, y) pairs.

Capacitive Touch Screen Technology(contd.)

Advantages

1. Can support multi touch gestures like flick, pinch and swipe

2.Are durabable

3. Last longer because there are no moving parts

4.Are sensitive and even a light touch can register an input

5.Are highly responsive

Capacitive Touch Screen Technology(contd.)

Disadvantages

1. Might not be able to work with non conductors of electricity like gloved fingers.

2. Affected by high humidity, dust and viscous fluids as they interfere with conductivity.

INTRODUCING FLAT PANEL DISPLAYS

1. The first computer monitors used CRT or Cathode Ray Tube technology, which was bulky and used a lot of power.

2. CRTs were impractical to use on notebooks, because of its weight and power consumption rates.

3. Flat panel screens or displays provided a form factor and power consumption rates that were practical to use with notebooks and this technology is predominantly used today.

FLAT PANEL DISPLAY TECHNOLOGY

1. The most common flat panel display technology in use today is the LCD or Liquid Crystal Display.

2. LCDs are made of viscous organic molecules that flow like liquid but have a chemical structure like crystals.

3. By using electric fields the optical properties of the crystalline liquid can be changed and this change manipulates light to create what we see on the screen.

FLAT PANEL DISPLAY TECHNOLOGY

1. Sandwiched between two parallel glass panels of an LCD is a volume of liquid crystals.

2. Transparent electrodes are used to manipulate the liquid crystals that in turn manipulate the light behind the rear plate. This process produces the image that we see on the screen.

3. Polarization filters are used on the front of the screen and on the rear of the front screen because the LCD technology requires filters to display images that you and I can see properly.

MONOCHROME FLAT PANEL LCD AND TFT DISPLAYS1. Two schemes can be used to control the electrodes that

manipulate the liquid crystals and they are passive and active matrixes.

2. The passive system uses just two parallel wires that intersect a pixel position and the horizontal line is pulsed to make that pixel change state from light to dark (monochrome).

3. By contrast the active system has an active switch that changes the pixel state on one of the electrodes at a given pixel position. The active system is called TFT (thin film transistor) displays.

4. TFT systems dominate the display market at present.

COLOR FLAT PANEL LCD DISPLAY

1. The color version of the LCD works essentially the same way as the monochrome but with added complexity.

2. The color version adds the optical filtering that separates light into its component parts, which are red, green and blue and it does this at every pixel position.

3. Every color can be built from the various combinations of these three primary colors.

FLAT PANEL DISPLAY

1. In summary, flat panel displays are predominantly in use today and they use the LCD technology. However, there are other technologies in the pipeline.

2. In fact, one of the more promising technologies is the Organic Light Emitting Diode or OLED displays. In short, voltages cause the organic molecule(s) to move to higher energy state.

3. When the voltage is removed the molecule(s) go back to their previous state and emit light in doing so.

VIDEO RAM1. Monitor is refreshed 60-100 times/sec from a special memory called video RAM. It has one or more bitmaps which represent the screen image.2. Say 1920*1080 pixels, which contains these values each pixel. It may contains many such bitmaps for fast switching from one screen to other.3. Garden variety display, represents each pixel as 3-byte RGB pixel color of red, green and blue. 4. Video RAM of 1920*1080 pixels at 3-bytes/pixel needs 6.2MB to store image. That’s why some computer uses 8-bit number to indicate color required.

VIDO RAM(CONT.)1. Color palette is made by this number as an index into hardware table, contains 256 entries each having 24-nit RGB values.2. It reduces RAM requirement by 2/3 but only allows 256 colors at once on screen.3. Generally each window has one mapping on its screen, but with one palette when multiple windows are present, only current one has its color showed properly.4. Palette with 2^16 is also used but gained 1/3 of it.5. To display full screen, multimedia on 1920*1080 display needs 6.2MB of data on each frame.6. For full motion video, 25 frame/sec for the data rate of 155 MB/sec is needed. 7. Original PCI can handle 132MB/sec but PCIe can handle this with ease.

INDIVIDUAL CONTRIBUTION

PREKSHA KASATWAR KEYBOARDSVIDEO RAMCOLLABORATE DOCUMENT

TIM ADAMS FLAT PANEL DISPLAYREVIEW THE DOCUMENT

DEEP PATEL TOUCH SCREENSREVIEW THE DOCUMENT