1. I/O Organization and Peripherals
Module V
I/O Organization and Peripherals

2. Polling Method
In this method, the controller generates the addresses for the masters.
Number of address line required depends on the number of master connected in the system. For example, if there are 8 masters connected in the system, at least 3 address lines are required.
In response to the bus request, the controller generates a sequence of master addresses.
When the requesting master recognizes its address, it activates the busy line and begins to use the bus.

3. Polling Method

4. Polling Method Advantages
The priority can be changed by altering the polling sequence stored in the controller
If one module fails, the entire system does not fail.

5. Independent Request
In this scheme each master has a separate pair of bus request and bus grant lines and each pair has a priority assigned to it.
The built in priority decoder within the controller selects the highest priority request and asserts the corresponding bus grant signal.

6. Independent Request

7. Independent Request Advantage:
Separate pairs of bus request and grant signals makes arbitration fast
Disadvantage:
It requires more bus request and grant lines.

8. Distributed Arbitration
In distributed arbitration, all devices participate in the selection of the next bus master.
In this scheme each device on the bus is assigned a 4-bit identification number.
When one or more devices request for the control of bus, they assert the start-arbitration signal and place their 4-bit ID numbers on arbitration lines, ARB0 through ARB3.

9. Distributed Arbitration
More than one device can place their 4-bit ID number to indicate that they need to control of bus.
If one device puts 1 on the bus line and another device puts 0 on the same bus line, the bus line status will be 0.
Device reads the status of all lines through inverters buffers so device reads bus status 0 as logic 1.
The device having highest ID number has highest priority.

10. Distributed Arbitration

11. Distributed Arbitration
When two or more devices place their ID number on bus lines then it is necessary to identify the highest ID number from the status of bus line.
Consider that two devices A and B, having ID number 1 and 6, respectively are requesting the use of the bus.
Device A puts the bit pattern 0001, and device B puts the bit pattern 0110.
With this combination the status of bus-line will be 1000; however because of inverter buffers code seen by both devices is 0111.

12. Distributed Arbitration
Each device compares the code formed on the arbitration line to its own ID, starting from the most significant bit.
If it finds the difference at any bit position, it disables its drives at that bit position and for all lower-order bits.
It does so by placing a 0 at the input of their drive.

13. Distributed Arbitration
In our example, device detects a different on line ARB2 and hence it disables its drives on line ARB2, ARB1 and ARB0.
This causes the code on the arbitration lines to change to This means that device B has won the race.
The decentralized arbitration offers high reliability because operation of the bus is not dependent on any single device.

14. Distributed Arbitration

15. I/O Devices
Peripheral devices refer to any external device connected to the computer.
Computer peripherals can be divided into two categories:
Devices that perform input and output operations: Examples : Keyboard, Mouse, Printer, Video Display, etc
Devices for the secondary storage of data Examples : Magnetic disk, Floppy Disk, CD ROM, etc

16. Peripheral devices Peripheral devices to be studied in detail include:
Scanner
Plotter
Joysticks
Touchpad

17. UQ : Write short note on Scanners

18. Scanners
Scanners transform printed material and photographs into digital representations.
Most scanners use a flat-bed arrangement, in which the page being scanned is placed over a flat glass surface.
A source of light scans the page, and the reflected light is focused on a linear array of charge coupled devices (CCDs).
When a CCD device is exposed to light, an electrical charge is stored in a tiny capacitor associated with it such that the amount of charge is proportional to the intensity of light.
This charge is collected by appropriate circuitry and converted to a digital representation using an analog to digital converter.

19. Scanners
For color scanners, red green and blue filters are used to separate the primary colors and process them separately.
As the light source moves across the page, the sensor array is read repeatedly, thus sampling the successive lines of pixels of image.
After scanning the image is represented in memory as an array of pixels.

20. Scanners

21. UQ : Write short note on Plotters

22. Plotters
A plotter is a printer that interprets commands from a computer to make line drawings on paper with one or more automated pens.
The plotter can draw continuous point-to-point lines directly from vector graphics files or commands.
There are different types of plotters:
a drum plotter draws on paper wrapped around a drum which turns to produce one direction of the plot, while the pens move to provide the other direction;
a flatbed plotter draws on paper placed on a flat surface; and
an electrostatic plotter draws on negatively charged paper with positively charged toner.

23. Plotter

24. Plotters
Plotters were the first type of printer that could print with color and render graphics and full-size engineering drawings.
Plotters are much more expensive than printers.
They are most frequently used for
CAD (computer-aided design) and
CAM (computer-aided manufacturing).
Hewlett-Packard is the leading vendor of plotters worldwide

25. UQ : Write short note on Joysticks

26. Joysticks
Joystick is a short pivoted stick that can be moved by hand to point in any direction in the X-Y plane.
When this information is sent to the computer, the software moves the cursor on the screen in the same direction.
The position of the stick can be sensed by a suitable linear or angular position transducer, such as the potentiometer arrangement.
The voltage outputs of the X and Y potentiometers are fed to two analog-to-digital convertors , whose outputs determine the position of the joystick and thus the desired direction of motion

27. Joysticks

28. Joysticks Joysticks are widely used in video games.
For use in video games, the joystick is shaped into a handle that suits the nature of the game.
It is usually equipped with push buttons to be used for shooting a ball or firing a gun.

29. Joysticks

30. UQ : Write short note on Touchpad

31. Touchpad
The touchpad is a small pad made of pressure sensitive material.
When the user’s finger touches some point on the pad, the pressure causes the electrical characteristics of the material at that spot.
The location of the spot is detected and communicated to the computer.

32. Touchpad
By moving a finger across the pad, the user can instruct the software to move the cursor on the screen in the same direction.
This makes touchpad a low cost replacement for the mouse, with high degree of robustness and reliability because it contains no moving parts.

33. Touchpad
The most innovative material for implementing touchpad is the one that has a large number of optical fibers embedded in it.
The material can identify the location of an object touching it as well as the amount of pressure being applied.
This material was developed for robotic applications in space.
A touchpad can be combined with a liquid crystal display to produce a touch sensitive screen that can be used for both input and output operations.

34. Touchpad