CS302 Midterm Notes 8 Files Merged by Jamil Hussain

CS304 Mid term Notes

Lec 1 to 22

Analogue versus Digital

Most of the quantities in nature that can be measured are continuous range having a minimum and maximum value. The temperature values in a summer month change between 23 0 C to 45 0 C. A car can travel at any velocity between 0 to 120 mph.

Digital representing of quantities

Digital quantities unlike Analogue quantities are not continuous but represent quantities measured at discrete intervals. A more accurate representation of the continuous signal is possible if the number of samples and sampling intervals are increased.

Electronic Processing of Continuous and Digital Quantities

Electronic Processing of the continuous quantities or their Digital representation requires that the continuous signals or the discrete values be converted and represented in terms of voltages.

There are basically two types of Electronic Processing Systems.

I. Analogue Electronic Systems: These systems accept and process continuous signals represented in the form continuous voltage or current signals. The continuous quantities are converted into continuous voltage or current signals by transducers. II. Digital Electronic Systems: These systems accept and process discrete samples representing the actual continuous signal. Analogue to Digital Converters are used to sample the continuous voltage signals representing the original signal.

Example The number 39 is represented by the calculator in terms of voltage as 39 mV. Digital Systems do not use discrete samples represented as voltage values. Digital Systems and Digital Values

Digital systems

Digital systems are designed to work with two voltage values. A+ 5 volts represents a logic high state or logic 1 state and 0 volts represents a logic low state or logic 0 state.

For example,

•  The numbers ‘0’ and ‘1’
•  The state of a switch ‘on’ or ‘off’
•  The color ‘black’ and ‘white’
•  The temperature ‘hot’ and ‘cold’
•  An object ‘moving’ or ‘stationary’

Digital Systems are based on the Binary Number system which allows more than two or multiple values to be represented very conveniently.

Each digit or bit in Binary Number system can represent only two values, a ‘0’ and a ‘1’. A single digit of the Decimal Number system represents 10 values, 0, 1, 2 to 9. A Combination of Binary Numbers is used to represent different quantities.

• Represent Colors: A palette of four colors red, blue, green and yellow can be represented by a combination of two digital values 00, 01, 10 and 11 respectively.
• Representing Temperature: An analogue value such as 39o C can be represented in a digital format by a combination of 0s and 1s. Thus 39 are 100111 in digital form.

The number of digits (0s and 1s) that represents a quantity is proportional to the range of values t.

Advantages of working in the Digital Domain Long Question may be

• Storing and processing data in the digital domain is more efficient: Computers are very efficient in processing massive amounts of information and data. Computers process information that is represented digitally in the form of Binary Numbers.
• Transmission of data in the digital form is more efficient and reliable: Modern information transmission techniques are relying more on digital transmission due to its reliability as it is less prone to errors.
• Detecting and Correcting errors in digital data is easier: In the Digital Logic Design course a simple method to detect single bit errors using the Parity bit will be considered
• Digital systems are easy to design and implement: Digital Systems are based on two states Binary Number System. Consequently the Digital Circuitry is based on the two voltage states, performing very simple operations.
• Digital circuits occupy small space: Digital circuits are based on two logical states. The PC motherboard having an area of approximately 1sq has most of the circuitry of a powerful computer.

Information Processing by a Digital System

I. Numbers II. Text III. Drawings, Diagrams and Pictures IV. Music and Sound

Characters used in writing text are represented through yet another standard known as ASCII which allows alphabets, punctuation marks and numbers to be represented through a combination of 0s and 1s.

Digital Components and their internal working

Digital system process binary information electronically through specialized circuits designed for handling digital information. These specialized electronic circuits are known as Logic Gates and are considered to be the Basic Building Blocks of any Digital circuit.

These gates are implemented using standard CMOS and TTL technologies that determine the operational characteristics of the gates such as the power dissipation, operational voltages (3.3v or 5 v), frequency response etc.

Combinational Logic Circuits and Functional Devices

Different gates are combined to build a circuit that is capable of performing some useful operation like adding three numbers. Such circuits are known as Combinational Logic Circuits or Combinational Circuits. Implementing large digital system by connecting