The History Of The Temperature Monitoring System

Published Date: 02 Nov 2017

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UNIVERSITY OF PRETORIA

The University of Pretoria places great emphasis upon integrity and ethical conduct in the

preparation of all written work submitted for academic evaluation.

While academic sta_ teach you about referencing techniques and how to avoid plagiarism, you

too have a responsibility in this regard. If you are at any stage uncertain as to what is required,

you should speak to your lecturer before any written work is submitted.

You are guilty of plagiarism if you copy something from another author's work (e.g. a book,

an article or a website) without acknowledging the source and pass it o_ as your own. In e_ect

you are stealing something that belongs to someone else. This is not only the case when you copy

work word-for-word (verbatim), but also when you submit someone else's work in a slightly altered

form (paraphrase) or use a line of argument without acknowledging it. You are not allowed to

use work previously produced by another student. You are also not allowed to let anybody copy

your work with the intention of passing if o_ as his/her work.

Students who commit plagiarism will not be given any credit for plagiarised work. The matter

may also be referred to the Disciplinary Committee (Students) for a ruling. Plagiarism is regarded

as a serious contravention of the University's rules and can lead to expulsion from the University.

The declaration which follows must accompany all written work submitted while you are a

student of the University of Pretoria. No written work will be accepted unless the declaration has

been completed and attached.

Full names of student:

Student number:

Topic of work:

Declaration

1. I understand what plagiarism is and am aware of the University's policy in this regard.

2. I declare that this assignment report is my own original work. Where other people's work

has been used (either from a printed source, Internet or any other source), this has been

properly acknowledged and referenced in accordance with departmental requirements.

3. I have not used work previously produced by another student or any other person to hand

in as my own.

4. I have not allowed, and will not allow, anyone to copy my work with the intention of passing

it o_ as his or her own work.

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Contents

1 Introduction 1

2 Flow Diagram 2

3 Implementation 3

3.1 System Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.1.1 CPU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.1.2 IO device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.1.3 Thermometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.2 Input and Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.2.1 Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.2.2 VGA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4 I/O Method Comparison 4

4.1 Programmed I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.1.1 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.1.2 Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.2 Interrupt Driven I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.2.1 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.2.2 Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.3 Direct Memory Access (DMA) . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4.3.1 Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4.3.2 Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1 Introduction

1

2 Flow Diagram

2

3 Implementation

3.1 System Hardware

3.1.1 CPU

3.1.2 IO device

3.1.3 Thermometer

3.2 Input and Output

3.2.1 Keyboard

3.2.2 VGA

3

4 I/O Method Comparison

4.1 Programmed I/O

Programmed I/O (PIO) refers to data transfers initiated by a CPU under driver software

control to access registers or memory on a device. The CPU issues a command then waits

for I/O operations to be complete. As the CPU is faster than the I/O module, the problem

with programmed I/O is that the CPU has to wait a long time for the I/O module to be

ready for either receiving or transmitting of data.

The CPU, must repeatedly check the status of the I/O module, and this process is known

as Polling. As a result, the level of the performance of the entire system is not very good.

Special instructions for the I/O are included in the ISA.

A summary of the operation of a Programmed I/O is :

_ The CPU requests I/O operation

_ The I/O module performs operation

_ The I/O module sets status bits

_ The CPU checks status bits periodically

_ The I/O module does not inform CPU directly

_ The I/O module does not interrupt CPU

_ The CPU may wait or come back later

4.1.1 Advantages

_ A program and processor dedicated to wait and repeatedly tests the status and for IO

data transfer till the IO operation completes

4.1.2 Disadvantages

_ The program waits and tests the status. The waiting period for an asynchronous event

can be large.

_ Events that occur at times that the processor cannot predict but the CPU can quickly

provide for it.

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4.2 Interrupt Driven I/O

The CPU issues commands to the I/O module then proceeds with its normal work until

interrupted by I/O device on completion of its work.

For input devices, the devices interrupts the CPU when data is being received ad must

be fetched by the CPU. The action it takes depends on whether it uses IO ports or memory

mapping.

For output devices, the devices sends an interrupt when it is ready to receive new data

or to acknowledge successful receipt of data. Although using interrupts takes away the need

for the CPU to have to wait for devices, its ine_cient for large amounts of data because the

CPU must transfer word by word, between the IO module and memory.

A summary of interrupt driven IO is given by :

_ The CPU issues a read command

_ The I/O module gets data from the peripheral while the CPU continues woking

_ The I/O module interrupts the CPU

_ The CPU requests to receive data

_ the I/O module transfers data

4.2.1 Advantages

_ Data only transferred when an interrupt is _red, only when it is ready

_ CPU can continue with work while IO receives data

4.2.2 Disadvantages

_ With many devices CPU may be disabled for large periods of time, because of many

interrupts

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4.3 Direct Memory Access (DMA)

Direct Memory Access means the CPU grants the IO module the ability to read or write

to memory without involving the CPU. The DMA module controls the exchange of data

between memory and the IO. Because of the DMA controller the data can be transferred

directly and relieves the load on the bus. The CPU only works on the beginning and end of

a transfer and is interrupted only after all the data is received.

The DMA uses hardware called the DMA controller which managed the data transfer. They

are programmed with pointers where to read/write the data, and are able to keep track of

the amount of bytes and settings which include interrupts and states. The DMAC increases

the system performance by allowing the CPU to perform tasks while data is being transferred

via the system and memory bus. In a system the DMA must be allowed to control a bus.

The CPU passes all I/O requests to the DMA controller.

When the CPU needs to read or write data, it gives a command to the DMAC with the

address of the IO device, the starting location of the data, the number of words in the data,

and whether to read or write.

4.3.1 Advantages

_ Computer system performance is improved by direct transfer of data between memory

and IO device by bypassing the CPU

_ CPU is free to perform operations that do not use the system buses

4.3.2 Disadvantages

_ Requires extra hardware to be implemented (DMAC)

_ Using the same bus as the CPU it may interrupt the CPUs use of the buses for long

periods of time, depending on data size

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