P. 6.1 Digital Technology and Computer Fundamentals Chapter 6 Computer Organization II

P. 6.2 Objectives n At the end of this chapter, you should be able to: u describe the characteristics of different input and output devices; u explain why I/O interfaces are required in a computer system;

P. 6.3 Objectives (Cont’d) u describe the three different methods for interfacing I/O; and u explain the advantage and disadvantages for each of the I/O interface methods.

P. 6.4 References u M. Marris Mano, "Computer System Architecture," third edition, Prentice Hall. u G. Shelly, T. Cashman, G. Waggoner, W. Waggoner, “Discovering Computers 98, A link to the Future,” International Thomson, 1998.

P. 6.5 Input / Output Devices n Provide communication for the CPU and the outside world u Keyboard u Mouse u Pointing Devices u Terminal u Visual Display Unit u Printers u Others

P. 6.6 Keyboard n Most commonly used n Keys are micro-switches. n Alphabetic keys. n Numeric keypad. n Arrow keys or cursor control keys n Function keys

P. 6.7 Mouse n A pointing device. n Controls the movement of an on- screen symbol called the pointer. n A ball or light reflection on the bottom to sense its movement. n Electronic circuits translate to electrical signals that are sent to the computer to direct the pointer.

P. 6.8 Trackball n Similar to a mouse n The ball is on top of the device.

P. 6.9 Touch pad n A flat surface usually attached in a notebook computer. n Controls the movement of the pointer by sensing the motion of a finger on its exterior.

P Pen n Pen input devices accept input with hand written characters. n Usually a special software must be required for this type of input. n Can also be used as a mouse

P Touch screen n Allows users to touch areas of the screen to enter data. n The action of screen-touching is equivalent to the movement and clicking the mouse. n Two types of touch screens: u combined with the monitor u attached in front of the monitor

P Image scanner n Electronically captures an entire page and converts the document into digital format. n Special software required to capture images. n To convert the image to text, Optical Character Recognition (OCR) software is needed.

P Optical recognition devices n Using a light source to read optical codes. n For example, a bar code reader reads the standard Universal Product Code (UPC) and converts them into digital format.

P Microphone n Accepts voice input n Voice recognition software is required to convert into digital format. n For voice to text conversion, familiarization is need for the conversion software to recognize the characteristics of the voice of the user.

P Terminal n Consists of a keyboard and a screen. n Dumb terminals have no independent processing capability. n Intelligent terminals have built-in processing capabilities. n Special purpose terminals uniquely designed for use in a particular industry.

P Visual Display Unit (VDU) n A visual output device. n A monitor looks like a television and consists of a cathode ray tube (CRT) display screen. n An LCD display is a thin display screen, and most often used in notebook computers.

P Printers n Used to produce hard copies. n Two categories: impact and non- impact printers. n Impact printers: striking a ribbon to deposit ink on the paper. n Non-impact printers: use some non-mechanical technique for printing.

P Dot-matrix printers n Consists of a printer head with a vertical column of 9 or 24 needles. n The needles are selectively energized and forced against the ribbon in proper combinations, to form the desired character image on the paper. n Major advantage: capability to print multiple copies simultaneously.

P Laser printers n Based on the principle of photocopying machines. n A laser beam produces mirrored images on a photo-sensitize selenium drum. n Toner gets stuck to the drum by an electrostatic process, then transferred to the paper.

P Laser printers (Cont’d) n Finally, The inked image on the paper is fused by heat. n Provide very good quality printing at a moderately fast rate.

P Ink-jet printers n Using the dot-matrix approach with droplets shot at the paper to form the desired character. n Quiet in operation with good print quality.

P Plotters n Used to produce high-quality line drawings. n Usually, the outputs of plotters are large size posters, graphics, etc.

P Data projectors n It takes the image that appears on a computer screen and project it. n It is a very effective method for presentation.

P I/O Interface n Usually, I/O devices are not connected directly to the system bus in the computer system. n An interface module for each device is needed.

P Need of interface module n I/O Operations are different from CPU and memory operations. n Operations of different peripheral devices are different. n Data format and word lengths are different. n Conversion of signal values for each device may be required.

P Need of interface module (Cont’d) n The data transfer rate of these devices are much slower than that of the memory or CPU. n Direct connection to the system bus is impractical.

P Solutions n Special hardware components are required to supervise and synchronize the input and output data transfer. n These components between the CPU and the peripheral devices are called interface.

P I/O Bus and Interface Modules n Each peripheral device connects to a separate interface module n All interfaces are attached to the I/O buses.

P Interface Module n Each interface u decodes the address and control signals received from I/O bus; u interprets and provides signals for the peripheral controller; u synchronizes the data flow and supervises the transfer.

P Accessing I/O n CPU places an address on the address bus. n The addressed interface detects it and activates the path. Other devices are disabled. n CPU provides an I/O command in the control lines. n The interface selected responds and proceeds to execute it.

P I/O Bus and Memory Bus n CPU communicates with both the I/O and the memory. n Memory bus contains data, address, and read/write control lines. n Need to separate them.

P Distinguish between I/O bus and Memory bus n Three different ways:  Two separate buses are used, one for memory and the other for I/O.  Common data bus and common address bus with separate control buses for memory and I/O.  All buses are common for memory and I/O.

P Separate buses for memory and I/O n Two independent sets of buses, one for memory, other for I/O. n A separate I/O processor (IOP) is provided in addition to the CPU. n Memory communicates with both CPU and IOP through memory bus.

P Separate buses for memory and I/O (Cont’d) n IOP also communicates with the I/O devices through a separate I/O bus with its own address, data and control lines. n The purpose of the IOP is to provide an independent pathway for the transfer of information between external devices and internal memory.

P Isolated I/O n One common bus to transfer data and address information between memory or I/O and the CPU. n Separate read and write lines are used to distinguish the memory and I/O operations.

P Isolated I/O (Cont’d) n CPU places the address information on the address bus. n It then enables one of the two possible read/write lines (memory R/W or I/O R/W) to specify the operation. n Specified device will be activated.

P Isolated I/O (Cont’d) n Distinct input and output instructions are available. n Each is associated with the address of an interface because of the small number of I/O devices. n Thus, the program size reduced and decoding speed increased.

P Isolated I/O (Cont’d) n Extra cost for the separate sets of read/write buses.

P Memory-mapped I/O n Only one set of read and write signals and common address bus for both memory and I/O n The CPU treats an interface as being part of the memory.

P Memory-mapped I/O (Cont’d) n Each interface is assigned an address same as the one in the physical memory space. n The physical memory space cannot be used. n Therefore, the total number of memory address range is reduced.

P Memory-mapped I/O (Cont’d) n Usually, a segment of memory address space is reserved for interface. n References to these addresses will be ignored by the memory and responded by the specific I/O interface.

P Memory-mapped I/O (Cont’d) n No specific input or output instructions n All access to the I/O can be made used of the large amount of memory-reference instructions. n Increases the flexibility for the programmer to design programs.