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Input-Output Organization

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Overview

Peripheral Devices

Input-Output Interface

Asynchronous Data Transfer

Modes of Transfer

Priority Interrupts

Direct Memory Access

Input-Output Processor

Serial Communication

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Peripheral Devices

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Peripheral

On-line devices Devices under direct computer control

Read/write information to memory on CPU command

Peripheral Devices attached to the computer

Electromechanical/electromagnetic

Monitor/Keyboard

Printer Magnetic tape

Magnetic disk

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ASCII Alphanumeric Characters

American Standard Code for Information

Interchange

128 characters

94 printable 26 Uppercase, 26 Lowercase, 10 numeric, 32 special (%, *)

34 non-printable (control)

Abbreviated names

Format characters (BS - backspace, CR - carriage return) Information separators (RS - record separators, FS - file

separators)

Communication controls (STX - start of text, ETX - end of text)

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ASCII Alphanumeric Characters

Computer uses 8 bits for a character

Additional bit?

As the parity for character For other special characters (Italic, Greek)

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Input-Output Interface

Transfer information between internal storageand external peripherals

Resolves the difference between CPU andperipherals Signal value changes Transfer rate mapping

Data code format mapping

Control operating modes (not to disturb each other)

Interfaces supervise and synchronize transfers

Lies between processor bus and peripheraldevice (or its controller)

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O/I Bus and Interface Modules

I/O bus consists of

Data lines

Control lines

Address lines

Each peripheral is associated with its interface

unit

Decode address and control received

Interrupts for the device

Provide signals for device

Synchronize and supervise data flow

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Ind ependent I/O Bus

CPU

Interface Interface

Peripheral Peripheral

Memory

memorybus

Separate I/O instructions (in,out)

CPU

Interface Interface

Peripheral Peripheral

Memory

Lines distinguish betweenI/O and memory transferscommon memory

& I/O bu s

VME busMultibus-IINubus

40 Mbytes/secoptimistically

10 MIP processorcompletelysaturates the bus!

O/I Bus and Interface Modules

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Input-Output Interface

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I/O Bus and Interface Modules

Each interface has own address

Processor places address on address lines

Corresponding peripheral responds while others

are deactivated

Same time processor provides function code on

control lines

Interface executes function on peripheral

4 main command types

Control commands, status, output data, input data