Contents
I/O Organization
Input-Output Interface
Asynchronous Data Transfer
Asynchronous Serial Transmission
Modes of Data Transfer
Programmed I/O
Interrupt-Initiated I/O
Direct Memory Access (DMA)
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Input Output Organization - Information Technology - Lecture Slides, Slides of Information Technology
This lecture is part of lecture series on Information Technology course. This lecture includes: Input Output Organization, Input - Output Interface, Major Differences, I/O Bus and Interface Module, I/O Versus Memory Bus, I/O Processor, Asynchronous Data Transfer, Strobe Signal, Disadvantage of Strobe Signal, Principle of Handshaking, Asynchronous Serial Transmission, First in First Out Buffer, Fifo, Direct Memory Access, Dma Controller
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2012/2013
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Contents ^ I/O Organization ^ Input-Output Interface ^ Asynchronous Data Transfer ^ Asynchronous Serial Transmission ^ Modes of Data Transfer ^ Programmed I/O ^ Interrupt-Initiated I/O ^ Direct Memory Access (DMA)
I/O OrganizationThe Input / output organization of computer dependsupon^ the^ size^ of^ computer
and^ the^ peripherals connected to it. The I/O Subsystem of the computer,provides^ an^ efficient
mode^ of^ communication between^ the^ central^
system^ and^ the^ outside environment.
Input - Output InterfaceInput^ Output^ Interface
provides^ a^ method^
for transferring information between internal storage andexternal^ I/O^ devices.^
Peripherals^ connected^
to^ a computer^ need^ special
communication^ links
for interfacing them with the central processing unit.
Input - Output InterfaceThe^ purpose^ of^
communication^ link
is^ to
resolve the differences that exist between thecentral computer and each peripheral.
The Major Differences are:-3.^ Data codes and formats in the peripherals differfrom the word format in the CPU and memory.4.^ The operating modes of peripherals are differentfrom each other and must be controlled so as not todisturb the operation of other peripherals connectedto the CPU.
Input - Output Interface^ To^ Resolve^ these^ differences
,^ computer^ systems include special hardware components between theCPU and Peripherals to supervises and synchronizesall input and out transfers. These components arecalled^ Interface^ Units
because^ they^ interface between the processor bus and the peripheral devices.
I/O BUS and Interface ModuleEach Interface^ decodes^ the address and control received fromthe^ I/O^ bus,^ interprets^
them^ for^ peripherals^ and providessignals for the peripheral controller. It is also synchronizesthe data flow and supervises the transfer between peripheraland processor. Each peripheral has its own controller.
For example , the printer controller
controls the paper motion, the print timing.
I/O BUS and Interface ModuleThe control lines are referred as an I/O command. Thecommands are as following:^ Control command-^ A control command is issued toactivate the peripheral and to inform it what to do.^ Status command-^ A status command is used to testvarious status conditions in the interface and theperipheral.
Processor Interface^
DataAddressControl Interface InterfaceKeyboardPrinter MagneticanddisplaydiskterminalConnection of I/O bus to input-output devices
I/O BUS and Interface Module
I/O Versus Memory BusTo communicate with I/O, the processor must communicate with the memoryunit. Like the I/O bus, the memory bus contains data, address and read/writecontrol^ lines.^ There^ are^3
ways^ that^ computer^ buses^ can
be^ used^ to communicate with memory and I/O: i.^ Use two Separate buses , one for memory and other for I/O. ii.^ Use^ one^ common^ bus^ for
both^ memory^ and^ I/O^ but^
separate control lines for each. iii. Use one common bus for memory and I/O with common control lines.
Asynchronous Data TransferThis Scheme is used when speed of I/O devices do not matchwith microprocessor, and timing characteristics of I/O devicesis not predictable. In this method, process initiates the deviceand check its status. As a result, CPU has to wait till I/Odevice is ready to transfer data. When device is ready CPUissues instruction for I/O transfer. In this method two types oftechniques are used based on signals before data transfer.i. Strobe Controlii. Handshaking
Strobe SignalThe^ strobe^ control^ method
of^ Asynchronous^ data transfer employs a single control line to time eachtransfer. The strobe may be activated by either thesource or the destination unit.
Data Transfer Initiated by Source UnitIn the block diagram fig. (a), the data bus carries the binaryinformation from source to destination unit. Typically, the bus hasmultiple lines to transfer an entire byte or word. The strobe is asingle line that informs the destination unit when a valid data wordis available.The timing diagram fig. (b) the source unit first places the dataon the data bus. The information on the data bus and strobe signalremain in the active state to allow the destination unit to receive thedata.
Data BusSourceDestinationStrobe^ UnitUnit (a) Block Diagram Data Valid data Strobe (b) Timing DiagramDestination-Initiated strobe for Data Transfer