Input/Output

1. Input/Output Structured Computer Organization Lecture #5 Jahan Zeb

2. Buses • A collection of parallel wires used to connect the components of a computer • The motherboard contains the CPU chip, some slots for RAM, and various support chips • Also contains a bus, and sockets into which the edge connectors of I/O boards can be inserted • Sometimes there are two buses, a high speed one (for modern I/O boards) and a low-speed one (for older boards)

3. Input/Output Buses Physical Structure

4. Logical Structure of a Simple PC • Has a single bus used to connect the CPU, memory, and I/O devices • I/O Controller(s) • Direct Memory Access (DMA) • A controller that reads or writes data to or from memory without CPU intervention is said to be performing DMA • Interrupt/Interrupt Handler: check for errors, info OS i.e I/O is finished

5. Input/Output Buses (2) Logical Structure

6. Bus Usage and Terminologies • Bus is not only used by I/O controllers, but also by CPU for fetching instructions and data • Bus Arbiterdecides which goes next if CPU and I/O controllers wants to use bus at the same time • I/O device granted bus when needed, the process is called Cycle stealing • ISA, Industry Standard Architecture Bus • PCI, Peripheral Component Interconnect Bus

7. Input/Output Buses (3) A typical modern PC with a PCI bus and an ISA bus

8. Terminals: Keyboard, Monitor • Keyboards • Cheap keyboards have mechanical contact when depressed, better ones have sheet of elastometric material between keys and underlying printed circuit board • CRT Monitors • Cathode Ray Tube • Electron gun, each for Red, Green and Blue • Device producing image line by line is called Raster Scan device

9. CRT Monitors (a) Cross section of a CRT (b) CRT scanning pattern

10. Flat Panel Displays • CRTs are far too bulky and heavy • LCD (Liquid Crystal Display) technology • Two parallel glass plates between which is a sealed volume containing a liquid crystal • An light source at back for illuminating screen • Transparent electrodes, used to create electric field in liquid crystals • To control the image displayed: Different parts of the screen get different voltages

11. Construction of an LCD screen (a) The construction of an LCD screen. (b) The grooves on the rear and front plates are perpendicular to one another.

12. Mice • Small plastic box sits on table next to keyboard • Allow users to pint screen items • Mechanical Mouse, Optical Mouse

13. Printers • Monochrome Printers • Matrix printers • If 80 characters in a 5*7 matrix across the line, print line then consists of 7 horizontal lines, 5*80=400 dots • Each dot can be printed or not printed, depending on the character • Fig(a) illustrates the letter “A” printed on a 5*7 matrix • Print quality can be enhanced using circles overlap as shown in fig(b)

14. Matrix Printers (a) The letter “A” on a 5 x 7 matrix. (b) The letter “A” printed with 24 overlapping needles.

15. Laser Printers • Rotating precision drum • Light from laser is scanned along length of the drum much like electron beam in CRT • Rotating mirror is used to scan the drum • Line of dots reaches the toner (black powder reservoir) • The toner is attracted to those dots that are charged, thus forming a visual image of that line

16. Operation of a laser printer

17. Halftoning • Solution for printing images with gray values • Halftone dots for various gray scale ranges. • (a) 0 – 6. (b) 14 – 20. (c) 28 – 34. • (d) 56 – 62. (e) 105 – 111. (f) 161 – 167. • .

18. Color Printers • Color images can be viewed in two ways: • Transmitted light: CRT • Reflected light: Color Photographs • In theory every color can be produced by mixing cyan, yellow and magenta ink • All color printing systems use four inks: CYMK (K is for blacK) • The complete set of colors that a display or printer can produce is called its gamut

19. Problems with Color Printing • Color monitors use transmitted light; Color printers use reflected light • CRTs produce 256 intensities per color; color must halftone • Monitors have a dark background; paper has a light background • The RGB and CMYK gamuts are different

20. Ink Types • Dye-based Inks • Consist of color dyes dissolved in fluid carrier, give bright colors and flow easily, main disadvantage is that they fade when exposed to ultraviolet light • Pigment-based Ink • Contains solid particles of pigment suspended in a fluid carrier that evaporates from the paper, leaving the pigment behind, do not fade in time but not as bright as dye-based inks

21. MoDems • Two-level signals suffer considerable distortion when transmitted over a voice-grade telephone line, leading to errors • A pure sine wave known as carrier can be transmitted with relatively little distortions, this fact is exploited as the basis of most telecommunication systems • By varying frequency, amplitude or phase, a sequence of 1s and 0s can be transmitted, the process is called modulation

22. Character Codes • Each computer uses set of characters, i.e. 26 upper case letters, 26 lower case letters, digits 0-9, special symbols • To transfer these characters to computer, each one is assigned a number; i.e. a=1, b=2,…..z=26, the mapping of characters onto integers is called a character code

23. ASCII • American Standard Code for Information Interchange • Each ASCII character has 7 bits, allowing 128 characters in all • Fig(1) shows the ASCII code. Codes 0 to 1F are control characters and do not print • The ASCII print characters are straight forward. They include the upper and lower case letters, digits, punctuation marks and a few math symbols

24. ASCII Character Codes (1) The ASCII Character set: characters 0 – 31.

25. ASCII Character Codes (2) The ASCII Character set: characters 32 – 127.