1 Pertemuan 12 Input/Output Matakuliah: H0344/Organisasi dan Arsitektur Komputer Tahun: 2005 Versi: 1/1

2 Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : Menjelaskan konsep dasar Input/Output

3 Outline Materi External Devices I/O Modules Programmed I/O Interupt-Driven I/O Direct Memory Access I/O Channel and Processor The External Interface

4 Overview I/O module contains logic for performing a communication between the peripherals and the systems bus. The reasons why one does not connect peripherals directly to the system bus are as follows: 1.There is wide variety of peripherals with various methods of operation. 2.There is a difference between the data transfer rate of peripherals and that of the memory or processor. 3.Peripherals often use different data format and word lengths than the computer.

5 Overview

6 I/O module has two major functions: 1.Interface to the processor and memory via the system bus or central switch. 2.Interface to one or more peripheral devices by tailored data links. Overview

7 External devices We can classify external devices into three categories: 1.Human readable 2.Machine readable 3.Communication

8 Block diagram of an external device External devices

9 I/O modules The major functions or requirements for an I/O module fall into the following categories: 1.Control and timing 2.Processor communication 3.Device communication 4.Data buffering 5.Error detection Module function

10 I/O modules Module structure

11 Programmed I/O No interruptsUse of interrupts I/O to memory transfer through processor Programmed I/OInterrupt driven I/O I/O to memory transfer Direct memory access (DMA)

12 Programmed I/O

13 There are four types of I/O commands: 1.Control 2.Test 3.Read 4.Write Programmed I/O I/O Commands

14 Programmed I/O I/O Instructions AddressInstructionOperan d Comment 200Load AC“1”Load accumulator Stored AC517Initiate keyboard read 202Load AC571Get status byte Branch if Sign = 0202Loop until ready Load AC516Load data byte Memory mapped I/O

15 Programmed I/O I/O Instructions AddressInstructionOperandComment 200Load I/O5Initiate keyboard read 201Test I/O5Check for completion Branch Not Ready201Loop until complete In5Load data byte Isolated I/O

16 Interrupt driven I/O Interrupt processing

17 Interrupt driven I/O Interrupt processing

18 Interrupt driven I/O Design issue 1.Because there will almost invariably be multiple I/O module, how does the processor determine which device issued the interrupt? 2.If multiple interrupt have occurred, how does the processor decide which one to process? Four general categories of technique are in common use: 1.Multiple interrupt lines 2.Software poll 3.Daisy chain (hardware poll, vectored) 4.Bus arbitration (vectored)

19 Intel 82C59A Interrupt Controller

20 Intel 82C55A Programmable Peripheral Interface

21 Direct Memory Access Drawbacks of programmed and interrupt driven I/O 1.The I/O transfer rate is limited by the speed with which the processor can test and service a device. 2.The processor is tied up in managing an I/O transfer; a number of instructions must be executed for each I/O transfer.

22 Direct Memory Access Block diagram

23 Direct Memory Access DMA and interrupt breakpoints during an instruction cycle

24 Direct Memory Access Alternative DMA configuration

25 Direct Memory Access The evolution of the I/O function 1.The CPU directly controls a peripheral device. 2.A controller or I/O module is added. The CPU uses programmed I/O without interrupts. 3.The same configuration as in step 2 is used, but now interrupts are employed. 4.The I/O module is given direct access to memory via DMA. 5.The I/O module is enhanced to become a processor in its own right, with a specialized instruction set tailored for I/O. 6.The I/O module has a local memory of its own and is, in fact, a computer in its own right.

26 Direct Memory Access I/O channel architecture

27 The external interface Type of interface One major characteristic of the interface is whether it is serial or parallel. The I/O module must engage in a dialogue with the peripheral. In general, the dialogue for a write operation is as follows: 1.The I/O module sends a control signal requesting permission to send data. 2.The peripheral acknowledges the request. 3.The I/O module transfers data. 4.The peripheral acknowledges receipt of the data. Key to the operation of an I/O module is an internal buffer that can store data being passed between the peripheral and the rest of the system. This buffer allows the I/O module to compensate for the differences in speed between the system bus and its external lines.

28 The external interface Point to point and multipoint configuration The connection between an I/O module in a computer system and external devices can be either point to point or multipoint.