Lec 1

Chapter One
1.1 Introduction:
Numbers are used to express quantities. There are many numerations systems used in the field of digital electronics, one of the most important being the binary system of numeration on which is based the computer science. Each of the various numerations systems and codes has its advantages but also inconvenient. The aim of this chapter is to present and explain the most common numeration systems and codes used in the conception of digital circuits.
1.2 Digital versus Analogue representation:
There are two basic ways we can represent quantities: Analogue representation and digital representation. With analogue representation, the quantity is symbolised in a way that is infinitely divisible. With digital representation, the quantity is symbolised in a way that is discretely packaged.
Example 1.1:
? The height of the red column which indicates the temperature measured by a thermometer is an analogue representation.
? An electronic watch whose digits changes second after second, minute after minute, shows a digital representation.
The comparison between digital and analogue representations can be given as in the following chart:
Analogue representation
Digital representation
Infinitely divisible
Discrete (Step by step)
Prone to errors of precision
Absolute precision
1.3 Systems of numeration:
To represent quantities in the different systems of numeration, specific symbols are used, which are also called ciphers.