Microcontrollers and Embedded Systems

Microcontrollers and

Embedded Systems

Thorough 8051 Microcontroller

Over 135 programming examples

Includes 15 I/O devices interfacing examples

Introduction to Advance Microcontrollers and RTOS

MOHIT TYAGI

ARVIND KUMAR GUPTA

ESCS LABS-Gr. NOIDA

Microcontrollers and Embedded Systems (The 8051 Microcontroller Architectural detailed explanation, Assembly language programming, interfacing with peripheral devices,

introduction to the 8096, MC68H11 and ARM processor, an overview on embedded systems design and RTOS)

Mohit Tyagi B.Tech., M.Tech. (MANIT-Bhopal)

(Training and R&D cell, ESCS Labs-Greater Noida)

Edited by

Er. Arvind Kumar Gupta (Project Manager in RMRC-Delhi and Technical advisor in ESCS Labs-Greater Noida)

PREFACE

This text book is intended for a course entitled Microcontrollers and Embedded Systems written for engineering students (GBTU, MMTU, KU, RTU, PTU, IP, MDU, RGPV etc.).

Now-a-days the microcontrollers have become the most powerful tools available to

the engineers. A small microcontroller in the fan control provides programmable speed control and temperature level of the room. High end industrial products can

contain over fifty embedded microcontrollers. A typical middle class household has over fifty embedded devices. For every PC, smart phone in the world there are over

one hundred embedded devices. Millions of PCs are manufactured each year, but billions of microcontrollers manufactured annually. While a great deal of attention is given to personal computers, the vast majority of new designs are for embedded

applications. For every PC designer, there are thousands of designers using microcontrollers in embedded applications. The number of embedded designs is

growing quickly. Architecture of the Microcontroller, especially assembly programming seems quiet complex to understand. Therefore, this book is designed to provide the desirable

balance among the basic concepts of architecture design, programs and interfacing. The main objectives of this book are to teach students the fundamental concepts of

the 8051 microcontroller, and logical programming oriented approach, which will help students who want to firm grasp on microcontroller applications, assembly programming and interfacing to the memory and I/O devices.

The I/O devices such as motors, sensors, ADC, DAC, keyboard, memory, buzzer, speaker, programmable chips, LCD, LED, seven segment display etc., are magnify

microcontroller operations and applications.

Assembly programming is an important aspect, without the knowledge of the

internal architecture, it is not possible to make a good assembly program. Emphasis is given to the microcontrollers and entire peripherals architecture, pin configuration and mode of operations.

This book contains twenty two chapters. The objectives of the course and the book are the same to describe the right way to design embedded systems. While no prior

knowledge of microcontrollers or microprocessors is required, but the reader should be familiar with basics of electronics, logic, and computer organization.

Learning to design and develop a microcontroller system without any practical hands-on experience is a bit like trying to learn to drive a car from reading book.

Thus, another goal is to provide a practical example of a complete working module.

Students are advised to work out all the review questions and then proceed to the next chapter. The review questions will refresh the contents of that chapter

discussed. This way will help you a lot for embedded systems design.

Authors

ABOUT THE AUTHORS Mohit Tyagi has over 6 year experience in industry, research and teaching. He holds graduate

degree in department of Electronics and Instrumentation Engineering and Master Degree in VLSI

and Embedded System Design from Maulana Azad National Institute of Technology (MANIT)-

Bhopal. He has published several research papers in National/ international journals. His areas of

working and current interest in computer architecture design (VLSI), embedded system, and

analog signal processing. He is a co-founder and working in training and research cell of ESCS

Labs-Greater Noida. The ESCS Labs is dedicated to spread knowledge in the field of VLSI design,

digital design, embedded system design and consumer electronics products design.

Arvind Kumar Gupta has a Bachelor of Technology degree in Electronics and communication.

He is working as a research associate in RMRC-Delhi; also serve as technical advisor in ESCS

Labs-Greater Noida. He has published several research papers in national/ international journals

and conferences. His areas of interest SMPS design, microcontroller based product design,

computer architecture and consumer electronics product design.

ESCS LABS- Greater Noida Published in Bharat ESCS Labs 2014

All rights reserved.

For suggestions and queries you can mail at: [email protected], [email protected] , www.escslabs.com

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CONTENTS

CHAPTER 1

INTRODUCTION TO DIGITAL SYSTEM 1

1.1 Number system 1

1.2 Logic Gate 4

1.3 Flip-Flop 6

1.4 Mux and De-mux 6

1.5 Basic input and output logic devices for interface 7

1.6 Registers 8

1.7 Arithmetic and Logical unit 9

Review Questions 11

CHAPTER 2

INTRODUCTION TO THE COMPUTER SYSTEM 12 2.1 Explanation of terms related to the microprocessors 13

2.2 Microprocessor 14

2.3 Introduction to Microprocessor based system 15

2.4 Microcontroller 16

2.5 Computer Architectures 17

CISC 17

RISC 18

2.6 Memory Architecture 18

Von-Neumann or Princeton 18

Harvard 19

2.7 The 8, 16 and 32-bit Microcontrollers 19

CHAPTER 3

INTRODUCTION TO MICROCONTROLLER, EMBEDDED PROCESSOR AND SYSTEM

3.1 Introduction to the microcontroller

3.2 Embedded Processor and Application Awareness

3.3 Selecting the right Microcontroller Unit

3.4 Processor Technologies

3.5 Selection Process

3.6 Choosing the Right Processor Technology

3.7 What does the MCU Need to do in the System?

3.8 Finalizing the Selection

CHAPTER 4 THE 8051 MICROCONTROLLER

4.1 Introduction to the 8051 Microcontroller Family

4.2 Development/Classification of Microcontrollers

4.3 The 8051 Microcontroller Architecture

4.4 The Functional Block Diagram for the 8051

4.5 A Small 8051 Microcontroller (AT89C2051)

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CHAPTER 5

ASSEMBLY LANGUAGE PROGRAMMING 5.1 Structure of Assembly Language Program

5.2 Assembler

5.3 Assembling and Running an 8051 Program

5.4 Programming Model for the 8051

5.5 The 8051s Memory Organization

5.5.1 Internal RAM Organization

The PSW Register and the Flag Bits of the 8051

5.5.2 Internal ROM

5.6 Inside the 8051 Microcontroller

5.7 Internal Working of the Microcontroller 5.8 The 8051 Microcontroller Instruction Set Summary

CHAPTER 6

DATA TRANSFER INSTRUCTIONS, I/O PORT PROGRAMMING 6.1 Data Transfer (Copy) Instructions and Programs 6.2 The 8051 I/O Parallel Port Programming

CHAPTER 7

ADDRESSING MODES 7.1 Immediate/constant addressing

Register addressing

Direct addressing

Register indirect addressing

Indexed addressing

Implied addressing mode

7.2 Timing Effect of Addressing Modes

7.3 Flow Chart symbols and description

CHAPTER 8

BRANCHING INSTRUCTIONS, LOOPS AND PROGRAMS 8.1 Jump Instructions, Loop and Programs

Unconditional Jump Instructions

Conditional Jump Instructions

Nested Loop (Loop within a Loop)

Call Instructions and Programs

Time Delay Calculation (Software Method)

CHAPTER 9

ARITHMETIC INSTRUCTIONS AND PROGRAMS

9.1 Addition

9.2 Subtraction

9.3 BCD (Binary Code Decimal) Number System

9.4 Multiplication and Division

9.5 Increment/Decrement

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CHAPTER 10

LOGIC INSTRUCTIONS AND PROGRAMS

10.1 Logical Instructions

10.2 Rotate Accumulator

10.3 Swap Nibbles within Accumulator

10.4 ASCII and BCD Code for Decimal Digits

CHAPTER 11

SINGLE BIT HANDLING INSTRUCTIONS 11.1 Bit Handling Instructions 11.2 Interfacing of a LED With a Port Pin 11.3 The Code Conversion Techniques and Programming BCD to Binary/Hex Conversion Binary/Hex to BCD Conversion 11.4 BCD To Seven-Segment Code Conversion 11.5 BCD to Seven-Segment Code Conversion 11.6 Interfacing with Buzzer

CHAPTER 12

TIMER/COUNTER IN THE 8051 12.1 Timers Programming

12.2 Time Delay Generation (Hardware Approach)

12.3 Large Time Delay Generation (Mixed Approach)

12.4 Using Timers as Counters (Counter Programming)

CHAPTER 13

8051 SERIAL COMMUNICATION, SPI, I2C AND USB INTERFACE

13.1 Synchronous And Asynchronous Serial Communications

13.2 Asynchronous Serial Data Bit Format

13.3 The Rs-232 Standards

13.4 DCE and DTE Devices

13.5 Voltage Converters

13.6 Universal Asynchronous Receiver Transmitter (Uart)

13.7 Baud Rate Generation

13.8 Serial Port Programming to Transmitting and Receiving Data

13.9 Power Mode Control (Pcon) Register

13.10 SPI Bus Interface

13.11 I2C Bus Interface

13.12 The Universal Serial Bus (USB)

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CHAPTER 14

THE 8051 INTERRUPTS 14.1 Polling and Interrupt Based Data Handling Input/Output Devices

14.2 The 8051 Interrupts

14.3 Enabling and Disabling of Interrupts

14.4 Timer Interrupts

14.5 External Interrupts

14.6 Internal Interrupts

14.7 Interrupts Structure for the 8051

14.8 Interrupt Priority in the 8051

14.9 Nested Interrupt (Interrupt with an Interrupt)

14.10 Interrupt Latency

CHAPTER 15

DATA CONVERTERS AND INTERFACING

15.1 Digital To Analog Convertor

15.2 Interfacing an 8-Bit DAC (MC1408) With The 8051 Microcontroller

15.3 Analog to Digital Converter (ADC 804)

15.4 The ADC 804 Interfacing with the Microcontroller

15.5 ADC0808/0809 Chip with 8 Analog Channels

15.6 Serial ADC Chips

15.7 Temperature Measurement

15.8 Signal Conditioning

15.9 Analog Output

CHAPTER 16

INTERFACING WITH THE KEYBOARD, SEVEN SEGMENT DISPLAY, LCD AND MOTORS 16.1 Simple Keyboard and Seven Segment Display Interface

16.2 Matrix Keyboard Interfacing with the 8051

16.3 Interfacing To LCD Display

16.4 The 8051 Interfacing With THe Motors

16.5 Pulse Width Modulation (PWM)

CHAPTER 17

INTERFACING TO EXTERNAL MEMORY

17.1 Decoder as Address Decoder

17.2 Flip-Flop or Latch as the Basic Output Interface

17.3 Memory Expansion

17.4 Introduction to Address Decoding

17.5 External Memory Interfacing in 8051/8031

17.6 External Program ROM Interfacing 17.7 External Data Memory RAM

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APPENDIX A 232-244

MODEL QUESTION PAPER 252

QUESTION BANK

CHAPTER 18

THE 8051/31 INTERFACING WITH 8255 (EXPENDING I/O PORTS)

18.1 Interfacing of the 8051 Microcontroller with the 8255 PPI

18.2 Simple Keyboard and Seven Segment Display Interface

18.3 Matrix Keyboard Interfacing with the 8255

CHAPTER 19

INTRODUCTION TO ADVANCED MICROCONTROLLERS

19.1 Introduction to Intel 8096

19.2 Introduction to MC68HC11 Microcontroller

19.3 Introduction to ARM Processor

CHAPTER 20

INTRODUCTION TO EMBEDDED SYSTEM DESIGN

20.1 Inside An Embedded System

20.2 Design Parameters

20.3 Embedded Systems Design

20.4 Development Lifecycle Model

20.5 The Embedded Systems Model

20.6 Present Trends in Embedded System

20.7 Real-Time Embedded Systems

20.8 Software Partitioning

20.9 Hardware and Software Co-Design Model

CHAPTER 21

INTRODUCTION TO REAL-TIME OPERATING SYSTEM (RTOS)

21.1 Real-Time Operating System

21.2 The Scheduler

21.3 Multitasking

21.4 Scheduling Algorithms

21.5 Task and Task States

21.6 Priority Inversion

21.7 Why Operating Systems for Real-Time Applications

21.8 Task-Oriented Design

21.9 How does an RTOS Work?

21.10 CASE STUDIES of RTOS

1

CHAPTER-1 INTRODUCTION TO DIGITAL SYSTEMS

The basic concepts of digital are necessary to understand the software logic and hardware design of a

microprocessor/microcontroller based system. In this chapter, we are focusing on logic gates, number

systems, conversion and inside a CPU.

1.1 NUMBER SYSTEMS The number of digits or basic symbols in a number system is known as its base. The decimal system has a base of 10 because it uses 10 digits. Binary has a base of 2; octal has a base of 8 and hexadecimal a base of 16. The number of digits in any base (also called radix) N is exactly the same number N. For example, in the binary (N = 2) number system there are only two digits: 0 and 1; in the Octal (N=8) there are eight of them: 0, 1, 2, 3, 4, 5, 6, and 7; in the decimal (N = 10) there are ten of them: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. What if N exceeds 10? If N > 10, the missing digits come from the alphabet (usually disregarding the case.) Thus A stands for the decimal 10 in any number system with base greater than 10. The B stands for the decimal 11 in any number system with base greater than 11, and so on. Here is the list of hexadecimal (base 16) digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, and F. It is customary to prefix hexadecimal numbers with ()H or 16, octal with ()O or 8 , decimal with ()D or 10 and binary with ()B or 2. The table 1.1 show that the basics of conversion and the relation among the number systems.

Table 1.1: Number systems

Decimal (0-9)10

Binary (0-1)2

Ternary (0-2)3

Quintal (0-4)5

Octal (0-7)8

Hexadecimal (0-F)16

Base 36 number (0-Z)36

0 0 0 0 0 0 0

1 1 1 1 1 1 1

2 10 2 2 2 2 2

3 11 10 3 3 3 3

4 100 11 4 4 4 4

5 101 12 10 5 5 5

6 110 20 11 6 6 6

7 111 21 12 7 7 7

8 1000 22 13 10 8 8

9 1001 100 14 11 9 9

10 1010 101 20 12 A A

11 1011 102 21 13 B B

12 1100 110 22 14 C C

13 1101 111 23 15 D D

14 1110 112 24 16 E E

15 1111 120 30 17 F F

16 10000 121 31 20 10 G

17 10001 122 32 21 11 H

18 10010 200 33 22 12 I

19 10011 201 34 23 13 J

. . . . . . .

. . . . . . .

98 1100010 10122 343 142 62 2Q

99 1100011 10200 344 143 63 2R

100 1100100 10201 400 144 64 2S

101 1100101 10202 401 145 65 2T

. . . . . . .

. . . . . . .

999 1111100111 1101000 12444 1747 3E7 RR

1000 1111101000 1101001 13000 1750 3E8 RS

1001 1111101001 1101010 13001 1751 3E9 RT

2

Decimal to Binary Conversion Double Dabble: This is a very popular way to convert decimal numbers to binary numbers. In this method, we progressively divide the decimal number by 2, writing down the remainder after each division. The remainder, arranged in reverse order is result the required binary number. Let us convert decimal number 1310 into equivalent binary number. Step 1 Divide 13 by 2, 2) 13 ( 6 ------ Quotient is 6 12 LSB 1 remainder = 1 Step 2 2) 6 ( 3 ------ Quotient is 3 6 0 remainder = 0 Step 3 2) 3 ( 1 ------ Quotient is 1 2 1 remainder = 1 Step 4 2) 1 ( 0 ------ Quotient is 0 0 1 remainder = 1 MSB In final division, 1 does not divide by 2, therefore, the quotient is 0 with a remainder of 1. Hence, the binary equivalent of 1310 is 11012.

Example 1.1: Express the decimal number 5410 as a binary number. Solution:

54/2 = 27 ; remainder 0 27/2 = 13 ; remainder 1 13/2 = 6 ; remainder 1 6/2 =3 ; remainder 0 3/2 =1 ; remainder 1 1/2 =0 ; remainder 1

Thus 54 decimal = 110110B and in an 8-bit register the value would be 00110110B. It may be easier to use the weighted values of an 8-bit register to determine the binary equivalent of a decimal number i.e. to break the decimal number down to those weighted elements, which have logic 1 level as given in following lines:

Binary to Decimal Conversion We can express any decimal integer (a whole number) in units, tens, hundreds, thousands and so on. For instance, the decimal number 3056D may be written as

385610 = 3000 + 800 + 50 + 6

In power of 10, this becomes

385610 = 3(10)3 + 8(10)

2 + 5(10)

1 + 6(10)

0

Here each digit position has a weight or value. The sum of all the digits multiplied by their weights gives the total amount being represented. Binary Weight In a similar way we can rewrite any binary number in terms of weights. For example binary number 111B (7D) becomes 1112 = 100 + 010 + 001

3

In decimal it is 710 = 4 + 2 + 1 710 = 1(2)

2 + 1(2)

1 + 1(2)

o

= 1(4) + 1(2) +1 Procedure for Binary to decimal conversion

i) Write the binary number ii) Directly under the binary number, write weights from right to left. iii) Multiply the weight with corresponding binary digit. iv) Add the remaining weights to obtain the decimal equivalent.

Example 1.2: Convert a binary number 1012 into equivalent decimal number. Solution:

Step i) Binary Number : 1 0 1 Step ii) Binary Weight : 4 2 1 Step iii) Equivalent weight : 4 0 1 Step iv) Weight Sum : 4 + 0 + 1 = 510

Example 1.3: Convert binary number 101012 into equivalent decimal number. Solution:

Step i) : 1 0 1 0 1 Step ii) : 16 8 4 2 1 Step iii) : 16 0 4 0 1 Step iv) : 16 + 0 + 4 + 0 + 1 = 2110

Conversion of Binary Fractions into decimal Fraction How we calculate the decimal equivalent of 0.1012? In this case, the weight of digit positions to the right of the binary point is given by 1/2, 1/4, 1/8, 1/16, 1/32 and so on. In power of 2, the weights are given below:

2-1

, 2-2

, 2-3

, 2-4

and so on or in decimal form 0.5, 0.25, 0.125, 0.0625 and so on Hence, the decimal equivalent for the binary fraction 0.1012 can be calculated as bellow:

0.1 0 1 0.5 + 0 + 0.125 = 0.62510

Example 1.4: What is the decimal equivalent of binary fraction 0.11012? Solution: Step i) Binary Number : 0. 1 1 0 1 Step ii) Binary Weight : 2-1 2-2 2-3 2-4 Step iii) Equivalent weight : 0. 5 0.25 0.125 0.0625 Step iv) Weight Sum : 0. 5 + 0.25 + 0 + 0.0625 =0.812510 Hence, for conversion of binary number into decimal number we should remember the following format:

23 22 21 20 .

2-1 2-2 2-3

Binary point

Table 1.2: Binary Addition Example 1.5: Add binary numbers 10102 to 10112. Solution: Binary Decimal 1 0 1 0 1 0 +1 0 1 1 + 1 1 1 0 1 0 1 2 1 Table 1.3: Binary multiplication

A+B Carry Sum 0 + 0 0 0 0 + 1 0 1 1 + 0 0 1 1 + 1 1 0

4

Example 1.6: Multiply 1012 by 1102. Solution: Binary Decimal Hex 1 0 1 5 5 x1 1 0 x 6 x 6 0 0 0 3 0 1E 1 0 1 x 1 0 1 x x 1 1 1 1 0

1.2 LOGIC GATES The logic gate is somewhat similar to normal gate/door. When a gate is opened something is allowed to pass and when it is closed nothing is allowed to pass through. But logical gate thinks logically and then acts. It works with certain conditions. When all the conditions are fulfilled input is allowed to pass as output. A logic gate is a digital circuit with one or more inputs, but only one output. The output is high only for certain combinations of the input signals. We have different types of gates such as AND gate, OR gate, NOT gate etc. These can be designed with the help of switches, diodes, transistors and ICs. Let us discuss these gates one by one.

AND Gate The AND Gate has two or more inputs but only one output. When all the inputs are high (1), the output is high (1) otherwise it is low (0). This gate can be implemented with simple switches as shown in figure 1.2(a).

Figure 1.2: (a) AND gate drawn with simple switches A and B (b) Symbol for AND gate

In the figure 1.2 (a), the switches A and B are connected in series with the supply. When both the switches are ON (i.e. 1 or High), the bulb is ON (1 or High). If any of the switches is OFF (0 or Low), the bulb is OFF (0 or Low). Hence the combination of switches A and B is known as AND gate. The symbol of AND gate is shown in figure 1.2(b).

Truth Table A truth table gives details of various combinations of inputs and corresponding outputs. The truth table of AND gate is given in table 1.4. Table 1.4: Truth Table of AND Gate

Figure 1.3: The AND gate drawn with diodes Figure 1.4: Quad 2-input TTL/CMOS AND gates AND Gate can also be implemented with diodes as shown in figure 1.3. When either A or B input is low (0), D1 or D2 is forward biased and output Y is low (0). When both inputs A and B are high (1) together, the output Y is High (1). In the same way AND Gate can also be designed with the combinations of diodes and transistors or only transistors. The AND gate designed in IC form is shown in figure 1.4. This gate works on the logic of 'this and that' hence the name is AND gate.

Inputs Output (0 for off/low and 1 for on/high)

A B Y

0 0 1 1

0 1 0 1

0 0 0 1

AB Multiplication 0 0 0 0 1 0 1 0 0 1 1 1

5

OR Gate This gate has two or more inputs and one output. When any one or all the inputs are high (1), the output is high (1). Figure 1.5(a) and (b) show the OR gate designed with the help of switches and diodes, respectively. Table1.5: Truth table for OR gate

Figure 1.5: (a) The OR gates drawn with switches (b) The OR gate drawn with diodes From figure 1.5 (a), the bulb is glowing when switch A or/and B is ON (1 or High). In figure 1.5 (b) output Y is High (1) when either input A or B is high (1) making D1 or D2 to conduct. The symbol of OR Gate is shown in figure 1.6(a). The OR gates in IC form shows in figure 1.6 (b). This gate works on the logic of 'This or that', hence the name is OR gate.

Figure 1.6: (a) Symbol of OR gate (b) Quad 2-input TTL OR gates

NOT Gate The NOT gate has one input and one output. When the input is High (1), the out is low (0) and vice versa. The figure 1.7 shows NOT gate designed with a switch and a transistor. Table 1.6: Truth table for NOT gate

Figure 1.7: (a) The NOT gate drawn with a switch (b) The NOT gate drawn with a transistor

In figure 1.7(a), When the switch is ON (1 or High) the bulb is shorted and hence it does not glow (OFF or 0 or LOW). When switch is OFF (open or 0) the bulb is ON (1 or High). In figure 1.7 (b), When the input A is high (1) the transistor is forward biased and so it conducts making Y low (0). When the input A is low (0), the transistor is cut off and hence the output Y is high (1). Since the NOT gate inverts the sense of the output with respect to input, it is also called as an inverter. Figure 1.7 (c) and (d) shows NOT gates symbol and IC form. This gate works on the logic of negative; hence the name is NOT gate.

Figure 1.7: (c) Symbol for NOT gate (d) Quad TTL NOT gates

NAND Gate A NAND gate has two or more inputs and a single output. It is a combination of an AND gate and a NOT gate. The output of a NAND gate assumes the 0 state if and only if all the inputs assume the 1 state. Figure 1.8 shows the NAND gate designed with the help of switches, symbol of NAND gate and NAND gates in IC form.

A B Y

0 0 0

0 1 1

1 0 1

1 1 1

A (I/O) Y(O/P)

0 1

1 0

6

Table 1.7: Truth table for NAND gate

Figure 1.8: (a) NAND gate drawn with switches (b) NAND gate Symbol (c) Quad 2-input NAND gates

NOR Gate

A NOR gate has two or more inputs and a single output. It is a combination of an OR gate followed by a NOT gate. The output of a NOR gate assumes the 1 state if and only if all the inputs assume the 0 state. Figure 1.9 shows the NOR gate designed with the help of switches. NOR gate symbol and IC form in given in figure 1.9. Table 1.8: Truth table for NOR gate

Figure 1.9: (a) NOR gate drawn with switches (b) Symbol of NOR gate (c) Quad 2-input NOR gates The NAND and NOR gates are known as 'Universal Gates' as any gate or logical circuit can be implemented with them.

Exclusive OR Gate EX-OR gate (see figure 1.10) has two or more inputs and one output. The EX-OR gate produces a high output when either of the inputs is high, but not both. This is different from the traditional OR gate, which produces a 1 output when either one or both of the inputs are 1. The opposite of Ex-OR gate is Ex-NOR gate. Table 1.9: Truth Table for EX-OR gate

Figure 1.10: (a) Symbol of EX-OR gate (b) Implementation of EX-OR gate with AND, OR and NOT gates

1.3 FLIP-FLOP

A flip-flop (FF) is a bi-stable electronic circuit that has two stable states. The flip-flop also has memory unlike gates described in previous Sections, since its output will remain as set until something is done to change it. FF has two outputs, defined as Q and Q.Q and Q are complementary. D Flip-Flop: The RS flip-flop has two data inputs R and S. To store a high bit, we need a high S; to store a low bit, we need a high R. Generation of two signals to drive has disadvantages in many applications. Furthermore, something forbidden condition of both R and S high may occur in advertently. These problems are avoided in D flip-flop, which only a single data needs as input. Logic diagram, symbol and truth table of D-FF are shown in figure 1.11.

Figure 1.11: Logic diagram, symbol and truth table of D Flip-Flop

1.4 MULTIPLEXER AND DEMULTIPXER Multiplexers, sometimes called selectors, are combinatorial elements that function as a multi-position logical switches to select one of many inputs. Figure 1.12 (a) shows a common schematic representation of a multiplexer, often shortened to

Input Output

A B Y 0 0 1

0 1 1

1 0 1

1 1 0

Input Output

A B Y

0 0 1

0 1 0

1 0 0

1 1 0

Input Output

A B Y 0 0 0

0 1 1

1 0 1

1 1 0

7

MUX. A MUX has an arbitrary number of data inputs, often an even power of two, and a smaller number of selector inputs. According to the binary state of the selector inputs, a specific data input is transferred to the output. A truth table for a 4-to-1 MUX is shown in Table 1.10. Each selector input value maps to one, and only one, data input. A de-multiplexer, also called a DEMUX, performs the opposite operation of a MUX by transferring a single input to the output that is selected by select inputs. A DEMUX is drawn similarly to a MUX, as shown in figure 1.12 (b). Table 1.10: Four-to-One Multiplexer Truth Table Table 1.11: One-to-Four Demultiplexer Truth Table

Figure 1.12: (a) Four-to-one multiplexer. (b) One-to-four de-multiplexer.

A popular use for a DEMUX is as a decoder. A decoder produces a unique output corresponding to each input pattern. If the input line in figure 1.12 (b) is set to logic 0 (i.e., Din = 0), the 1-to-4 de-multiplexer will act as a decoder. For example, A = 0, B = 0 will give an output of 0 on line Y0; lines Y1, Y2, and Y3 will be at logic 1. Similarly, A = 0, B = 1 will give an output of 0 on line Y1; A = 1, B = 0 will give an output of 0 on line Y2; and A = 1, B = 1 will give an output of 0 on line Y3. Thus the 1-to-4 de-multiplexer can function as a 2-to-4 decoder. This function has great utility in microprocessor address or op-code decoding, which involves selecting one of multiple devices (e.g., a memory chip) at a time for access. The truth table for a 2- to-4 decoder is shown in table 1.12 and in figure 1.12 (c). The decoders outputs are active-low, because most memory and microprocessor peripheral chips use active-low enable signals.

Table 1.12: Two-to-Four Decoder Truth Table

1.5 BASIC INPUT AND OUTPUT LOGIC DEVICES FOR INTERFACE The interfacing logic devices are used to make compatible of I/O device to the microprocessor system. Also interfacing logic devices increase the current driving capacity of data/address lines. There are three basic interfacing devices:-

1. Tri-state buffers as bus drivers 2. Decoder 3. Latch

Tri-state/three-state buffer logic as the basic input interface: Three Logic Levels are used and they are as High, Low, and High impedance (1, 0 and z) state. The high and low are normal logic levels but high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line may be active Low or High. The various types of tri-state buffers are shown in figure 1.13.

DECODER

24

A

B

Y0

Y1

Y2

Y3

Figure 1.12(c): a 2 to 4 decoder

8

The only difference between tri-state buffer and two-state buffer (simply buffer) is that buffer does have high impedance state. Therefore, there is no need of third line to enable buffer as shown in figure 1.14. Input B Output Q Input B Output Q Input B Output Q Low Enable E High Enable E High Enable E Figure 1.13: (a) Active low, inverted output tri-state buffer (b) Active high, inverted output tri-state buffer (c) Active high, non inverted output tri-state buffer input output

Figure 1.14: A buffer

Active low, inverted O/P tri-state buffer: When enable E is low the gate is enabled and the output Q can be 1 or 0 (if B is 0, Q is 1, otherwise Q is 0). However, when E is high the gate is disabled and the output Q enters into a high impedance state. Table 1.13 is described the function of each pin of Low enabled tri-state buffer with inverting output.

Table 1.13: Functional table for active low, inverted output tri-state buffer

E ( Low Enable) B (Input) Q (Output) State description

1(High) 0 z High impedance (Open Circuit)

1 1 z High impedance (Open circuit)

0(Low) 0 1 High

0 1 0 Low

Active High, inverted O/P tri-state buffer: When enable E is high the gate is enabled and the output Q can be 1 or 0 (if B is 0, Q is 1, otherwise Q is 0). However, when E is low the gate is disabled and the output Q enters into a high impedance state.

Active High, non-inverted O/P tri-state buffer: When enable E is high the gate is enabled and the output Q can be 1 or 0 (if B is 0, Q is 0, otherwise Q is 1). However, when E is low the gate is disabled and the output Q enters into a high impedance state. The advantages of using tri-state buffer and two-state (normal) buffer

1- It can avoid undesirable change in input and control the read operation of the output of flip-flop.

2- Tri-state buffer have three states as high, low, and high impedance (open circuit). If any flip-flop

or register is not involved in any read or/and write operations, tri-state (high impedance

state) buffer disconnect this flip-flop or register from memory circuit by making open

circuit or high impedance so that there is no flow of any current in the circuit hence we

can save power dissipation.

3- Tri-state buffers or two state buffers are used to amplify current or power driving capacity of buses

to avoid loading effect. Loading effect means that when the microprocessor draws high load current

from input device is may cause overloading. Input device gives some fake or inaccurate output

value to the microprocessor as the overloading change the characteristics of the input device.

1.6 REGISTERS Registers are collections of multiple flip-flops arranged in a group with a common function. They are a

common synchronous-logic building block and are commonly found in multiples of 8-bit widths, thereby

representing a byte, which is the most common unit of information exchange in digital systems. An 8-bit

register provides a common clock and clock enable for all eight internal flip-flops. The clock enable allows

external control of when the flip-flops get reloaded with new D-input values and when they retain their

current values. It is common to find registers that have a built-in tri-state buffer, allowing them to be

placed directly onto a shared bus without the need for an additional tri-state buffer component.

Whereas normal registers simply store values, synchronous elements called shift registers manipulate

groups of bits. Shift registers exist in all permutations of serial and parallel inputs and outputs. The role of

a shift register is to somehow change the sequence of bits in an array of bits. This includes creating arrays

of bits from a single bit at a time (serial input) or distributing an array of bits one bit at a time (serial

output). A serial-in, parallel-out shift register can be implemented by chaining several flops together as

shown in figure 1.14.

9

Figure 1.14: Serial-in, parallel-out shift register.

On each rising clock edge, a new serial input bit is clocked into the first flop, and each flop in succession

loads its new value based on its predecessors value. At any given time, the parallel output of an N-bit shift register reflects the state of the last N bits shifted in up to that time. In this example (N = 4), a serial

stream of bits collected in four clock cycles can be operated upon as a unit of four bits once every fourth

cycle. As shown, data is shifted in MSB first, because Dout[3] is shown in the last bit position. Such a

simple transformation is useful, because it is often more practical to communicate digital data in serial

form where only one bit of information is sent per clock cycle, but impractical to operate on that data

serially. An advantage of serial communication is that fewer wires are required as compared to parallel.

A parallel-in, serial-out shift register is very similar, as shown in figure 1.15, with the signals connected

for MSB first operation to match the previous example. Four flops are used here as well. However, instead

of taking in one bit at a time, all flops are loaded when the load signal is asserted. The 2-to-1 muxes are

controlled by the load signal and determine if the flops are loaded with new parallel data or shifted serial

data. Over each of the next four clock cycles, the individual bits are shifted out one at a time. If these two

shift register circuits were connected together, a crude serial data communications link could be created

whereby parallel data is converted to serial and then back to parallel at each end.

Figure 1.15: Parallel-in, serial-out shift register

1.7 ARITHMETIC AND LOGICAL UNIT An arithmetic and logic unit (ALU) is a digital circuit that performs arithmetic and logical operations.

The ALU is a fundamental building block of the CPU of a processor. Most of a processor's operations are

performed by the ALU. An ALU loads data from input registers. Then an external control unit tells the ALU

what operation to perform on that data, and then

the ALU stores its result into an output register.

The control unit is responsible for moving the

processed data between these registers, ALU and

memory. In order to know that how an ALU works?

We are undergoing with its design in next sections.

The ALU Design

A basic ALU design involves a collection of "1-bit

ALU ", which each can perform the specified

operation on a single bit. Figure 1.16 shows a 1-bit

ALU that can perform AND, OR, and ADD

operations.

Figure 1.16: A 1-bit ALU circuit

10

A typical ALU is given in figure consists of various digital circuits such as decoder, multiplexer, de-

multiplexer, adder, subtractor, multiplication, division, logical AND, OR, NAND, NOR, EX-OR etc. The op-

code 01112= 7H enables the register A, register B and full adder circuit. To generate enable signal for it, a

decoder (control circuit) is used. An 8-bit ALU can be implemented (shown in figure 1.17) for the functions

as given in table 1.14. Table 1.14: Operations for ALU

Select (Op-code) Operation Instruction Function Unit 0000 Y=A MOV Y, A Transfer A

Arithmetic

0001 Y=A+1 INC A Increment A

0010 Y=A-1 DEC A Decrement A

0011 Y=B MOV Y, B Transfer B

0100 Y=B+1 INC B Increment B

0101 Y=B-1 DEC B Decrement B

0110 Y=A+B ADD A, B Add A and B

0111 Y=A+B+Cin ADDC A, B Add A and B with Carry

1000 Y=A CPL A Complement A

Logic Unit

1001 Y=B CPL B Complement B

1010 Y=A AND B AND A, B Logical AND with A and B

1011 Y=A OR B OR A, B Logical OR with A and B

1100 Y=A NAND B NAND A, B Logical NAND

1101 Y= A NOR B NOR A, B Logical NOR with A and B

1110 Y=A XOR B XOR A, B Ex-OR

1111 Y= A XNOR B XNOR A, B EX-NOR

The ALU has some stages, each stage consisting of three parts: a) input multiplexers b) full adder and c)

output multiplexers. The ALU performs the following four arithmetic operations, MOVE, ADD, INCREMENT

and DECREMENT. The four logical operations performed are NOT, Ex-OR, Ex-NOR, AND and OR. The input

and output sections consist of 8 to 1 and 2 to 1 multiplexers. A set of four select signals has been

incorporated in the design to determine the operation being performed and the inputs and outputs being

selected. Figure 1.17 shows the 8-bit ALU with the Cin bit cascading all the way from first stage to fourth

stage.

Figure 1.17: A typical 8-bit ALU

There are large numbers of digital circuits in a processor including ALU such as registers, counter,

multiplexer, decoder, adder etc. and every operation have a unique code, called Op-code. For example:

we want to move/copy the contents of a register (say B) to the output register (say Y). The instruction

MOV Y, B performs this operation and machine-code for this operation is 03H. The instruction-code

00112=03H enables the register Y, register B and parallel-in parallel-out register. To generate enable signal for it, a decoder (control circuit) is used. The internal operations of the processor circuit upon

receiving instruction code shown in figure 1.18. First, the decoder is decoding the instruction code, and

generate enable signal at the output. Shift register and register Y and B enable signal connected to the

decoder enable output.

11

0011 (Input)

(Output) Enable signal to shift register

Register B (source)

Enable

Register Y (destination) Figure 1.18: The internal circuit operation of a processor to execute MOV Y, B instruction

REVIEW QUESTIONS

1. Express decimal 167 as a binary number.

2. Represent decimal numbers 15 and 250 in binary format.

3. Convert Hex ABCD to binary.

4. Add 26H+AFH.

5. What is ALU purpose?

6. Express 101111000001 as a hexadecimal value.

7. Express decimal 100 as a hex number and then as a binary number.

8. Show that if an 8-bit register contains all logic 1s then the value stored is 255.

9. Describe the function of Mux and Demux.

10. Design a 4-bit ALU for two arithmetic and two logic operations.

D Q

CLK

D Q

CLK

D Q

CLK

D Q

CLK

D Q

CLK

D Q

CLK

D Q

CLK

D Q

CLK

D7 D6 D5 D4 D3 D2 D1 D0

D7 D6 D5 D4 D3 D2 D1 D0

Decoder

4 24

12

CHAPTER-2 INTRODUCTION TO THE COMPUTER SYSTEM

A digital computer is a digital electronic system which is designed to store, process, and communicate

information in digital form. The computer systems are constructed of digital electronics. It means that

their electronic circuits can exist in only one of two states: On or Off. Most computer electronics use voltage levels to indicate their present state. For example, a transistor with +5 volts would be considered

"on", while a transistor with 0 volt would be considered "off."

They are found in a wide range of applications, like process control, communication systems, digital

instruments, weather forecasting and consumer products such as PCs, handhold calculators, mobile

phones etc.

How many languages do we know? Most probably more than one, but digital computer knows only a

binary. A binary number has only two discrete values: 0 and 1. Each discrete value is represented by the

on (1) and off (0) status of an electronic switch called a transistor. These patterns of "on" and "off" stored inside the computer, which are used to encode binary data using the binary number system. The

binary number system is a method of storing ordinary numbers as pattern of 1's and 0's i.e. the ordinary

decimal number 810 is stored in computer as 01002 in binary. Because of their digital nature, the

electronics of computer can easily manipulate numbers stored in binary by treating 1 as "on" and 0 as

"off." The digital computer has various circuits, so that it can add, subtract, multiply, divide, and can do

many other things with numbers stored in binary. All digital computers understand only binary number patterns or binary codes. Any decimal number (base 10, with ten digits from 0 to 9) can be represented

by a binary number (base 2, with digits 0 and 1).Its Binary codes are the digital machine language. A

computer manipulates information in digital or more precisely in binary form.

Computer software consists of a collection of programs that contain instructions and data to perform a

task. All programs are written using any programming language (i.e. Assembly, C, C++, Java etc), must

be translated into binary prior to execution by a computer because the computer is a digital device.

Therefore, a translator is necessary to convert such a program into binary and this is achieved using a

translator program called a compiler.

A computer is a programmable machine. The two principle characteristics of a computer are: it responds

to a specific set of instructions in a well-defined manner and it can execute a prerecorded list of

instructions (a program). Modern computers are electronic and digital. The actual machinery wires,

transistors, and circuits are called hardware. The instructions and data are called software.

All general-purpose computers require the following hardware components:

Memory: Enables a computer to store data and programs permanent or/and temporarily. Mass storage device: Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.

Input device: Usually a keyboard and mouse is the input device through which data and instructions enter a computer.

Output device: A display screen, printer, or other device that lets you see what the computer has accomplished.

Microprocessor: The brain of the computer, this is the component that actually executes instructions (processes data according to instructions).

In addition to these components, there are many other components which make it possible for the basic

components to work together efficiently. For example, every computer requires a bus (signal lines/wires)

that transmits data from one part of the computer to another.

The basic blocks of a computer, are the central processing unit (CPU) or Microprocessor(s), the RAM and

ROM memory, and the input/output (I/O) ports or devices. The CPU or microprocessor (ALU + Reg.) of a

computer is basically the same as the brain of a human being; so computer memory is conceptually

similar to human memory.

A question asked to a human being is analogous to enter a program into a computer using an input device

such as a keyboard, touch-screen, scanner and a person answering a question is similar in concept to

outputting the program result to a computer output device such as a printer, monitor, alarm etc.

13

The main difference is that human beings can think independently, whereas computers can responds only

for those questions, which they are programmed (instructions) and designed (electronic circuit). So, one

can better understand who is more intelligent?

The computer hardware includes such components as memory, CPU, transistors, plug, socket, nuts, bolts,

and so on. These hardware components like CPU, memory are designed for software programs. The

programs can perform a specific task, such as addition, subtraction etc., if the computer has an electronic

circuit capable of adding two numbers. The programmers cannot change these electronic circuits but can

perform tasks on them using instructions.

All units (CPU, memory, and I/O devices ) of the computer work together in synchronization to perform a

task similar to human being, all parts of human body (brain as CPU and memory, Input units as eyes,

ears, nose etc. and output units as human voice, hands, lags etc) work together to perform a task.

In next paragraphs, we define some basic terms associated with microprocessor based systems.

2.1 EXPLANATION OF TERMS RELATED TO THE MICROPROCESSOR/COMPUTERS

Before we go on, it is necessary to understand some basic terms.

Signal A variable parameter by which information is conveyed through an electronic circuit or wire. Digital Signal Operating by the use of discrete signals to represent data in the form of numbers. A discrete-time signal having a set of discrete values is called a digital signal. Note that sampling an analog

signal produces a discrete-time signal. Then quantization of its values produces a digital signal.

An Address is a pattern of 0s and 1s that represents a specific location in memory or a particular I/O device. Typical 8-bit microprocessors have 16 address lines, and, these 16 lines can produce 216 unique

16-bit patterns from 0000 0000 0000 00002 to 1111 1111 1111 11112 (0000H to FFFFH) representing

65,536 different address combinations/memory locations.

An Arithmetic-logic unit (ALU) is a digital circuit that performs arithmetic and logic operations on two or

more n-bit digital words. The value of n can be 4, 8, 16, 32, or 64 Bits. Typical computing operations

performed by an ALU are addition, subtraction, ANDing, ORing, and comparison of two n-bit digital words.

The size of the ALU defines the size of the microprocessor. For example, a 32-bit microprocessor

contains a 32-bit ALU.

The Bit is an abbreviation for the term binary digit. A binary digit can have only two values, which are 0

and 1, whereas a decimal digit can have 10 values, represented by the symbols 0 through 9.

A number of bits taken as a group are called a word. For example, a 32-bit microprocessor can process a

32-bit word or 8-bit microprocessor can process an 8-bit word.

An 8-bit word is referred to as a byte, and a 4-bit word is known as a nibble. A byte contains two nibbles.

A bit is a single binary digit of value logic 1 or logic 0. A nibble is a group of bits, e.g. 10102 is a nibble. A

byte is a group of 8 bits e.g. 101001112 is a byte and the byte is made up of two nibbles 10102 and

01112.

The Microprocessor based system consist at least a microprocessor and input/output devices and Memory.

This is the difference between the microprocessor and the microprocessor based system (microcomputer).

A bus consists of a number of conductors (wires) organized to provide a means of communication or data

transfer among different elements in a microprocessor system. The conductors in a bus can be grouped in

terms of their functions. A microprocessor normally has an address bus, a data bus, and a control bus.

Address bits are sent to memory or to an external device on the address bus. The Instructions from

memory, and data to/from memory or external devices, normally travel on the data bus. The Control

signals for the other buses and among system elements are transmitted on the control bus.

Unidirectional Bus (generally used for Address Bus) Bidirectional Bus (generally used for Data bus) Unidirectional line (generally used for Address/control line) Bidirectional line (generally used for Data/control line)

14

The Clock is analogous to `human heart beats. The microprocessor requires synchronization among its

components, and this is provided by a clock or timing circuits i.e. the microprocessor is a synchronous

electronic integrated circuit.

The instruction set of a microprocessor is a list of operations/commands that the microprocessor circuit

is designed to execute. Typical instructions are ADD, SUBTRACT, and STORE individual instructions are

coded as unique bit patterns which are recognized and executed by the microprocessor. If a

microprocessor has 3 bits allocated to the representation of instructions, the microprocessor will recognize

a maximum of 23, or eight different instructions. In other word, the microprocessor will have a maximum

of eight instructions in its instruction set. It is obvious that some instructions will be more suitable than

others to a particular application. For example, if a microprocessor is to be used in a calculating mode, the

instructions/operations such as ADD, SUBTRACT, MULTIPLY, DIVIDE and LOGICAL OPERATIONS would be

desirable. In a control application, the instructions inputting digitized signals to the processor and

outputting digital control variables to external circuits are essential. The number of instructions necessary

in an application will directly influence the amount of hardware in the chip set and the number and

organization of the interconnecting bus lines.

The Pipelining is a technique that overlaps instruction fetch (instruction read) and instruction execution.

In other word, pipelining is the fetching of current instruction and execution of the previously fetched

instruction simultaneously. This allows microprocessors processing operation to be broken down into several steps (dictated by the number of pipeline levels or stages) so that the individual step outputs can

be handled by the microprocessor in parallel. The Pipelining is often used to fetch the microprocessors next instruction while executing the current instruction, which speeds up the overall operation of the

microprocessor considerably.

The Random-access memory (RAM) is storage medium for group of bits or words whose contents can

be read as well as altered at specific addresses (that is why it called read/write memory). A RAM normally

provides volatile storage, which means that its contents are lost in case power is turned off. RAMs are

fabricated on chips and have typical densities of 4096 bits to 1 megabit per chip. These bits can be

organized in many ways: for example, as 4096 x 1 bit words or as 2048 x 2 bit words. RAMs are normally

used for the storage of temporary data and intermediate results as well as programs that can be reloaded

from a backup nonvolatile source. RAMs are capable of providing large storage capacity, in the megabit

range.

The Read-only memory (ROM) is storage medium for the group of bits called words, and its contents

can easily read but cannot normally be altered once programmed. A typical ROM Is fabricated on a chip

and can store, for example, 2048 eight-bit words, which can be accessed individually by presenting to it

one of 2048 addresses. This ROM is referred to as a 2K x 8-bit ROM. 1011 01112 is an example of an 8-bit

word that might be stored in one location in this memory. A ROM is a nonvolatile storage device, which

means that its contents are retained in case power is turned off. Because of this characteristic, ROMs are

used to store programs (instructions and data) that must always be available to the microprocessor.

A register can be considered as volatile storage (RAM) for a number of bits. These bits may be entered

into the register simultaneously (in parallel) or sequentially (serially) from right to left or from left to right,

1 bit at a time. An 8-bit register storing the bits or 8-bit word 111100002 are represented as follows:

1 1 1 1 0 0 0 0

The word micro is used in electronics and in science generally, to mean one-millionth or 1 x 106. It has also entered general language to mean something very small circuit components fabricated by LSI or VLSI

technology for example, a very small processor or microprocessor. It has also become an abbreviation

for microprocessor, microcomputer, microprocessor-based system or a microcontroller indeed almost anything that has micro in its name. In the scientific sense, the word micro is represented by the Greek letter (mue). It was only a small step for microprocessor to become abbreviated to P.

2.2 MICROPROCESSOR (P) In general, it is a clock driven, multipurpose, programmable, semiconductor electronic device, fabricated

with LSI (Large Scale Integration) or VLSI (Very LSI) technology, contains several general purpose

registers (memory elements) including special purpose register such as program counter (PC) or

Instruction pointer and stack pointer, an ALU (arithmetic and logical unit), and a control and timing unit

on a single chip as shown in figure 2.1. In the world of personal computers, the terms microprocessor and

CPU are used interchangeably. One or more microprocessor typically serves as a central processing unit

15

(CPU) in a computer system or handheld device. Microprocessors made possible the advent of the

microcomputer. At the heart of all personal computers and most working stations sits a microprocessor.

The Microprocessors also control the logic of almost all digital devices, from handheld calculator to fuel-

injection systems for automobiles.

Notice that a microprocessor cannot work alone and must be interfaced with peripheral support chips

(memory, input-output devices etc.) in order to perform a function. The Microprocessor receives

instruction (binary code) from memory and accepts binary data input according to the command from

memory or input device and provide the result to the output device. Actually we do not work with only

microprocessor but a microprocessor based system (described in next topic). However, we study the

microprocessor to work with microprocessor based system. Three basic characteristics that differentiate

one microprocessor to other:

Bandwidth is the number of bits processed in a single instruction. Clock speed is given in megahertz

(MHz); the clock speed determines that how many instructions per second the processor can execute.

In above both cases, the higher the value of BW and clock speed, the more powerful will be the CPU. For

example, a 16-bit microprocessor that runs at 8MHz is more powerful than an 8-bit microprocessor that

runs at 3MHz. In addition to bandwidth and clock speed, the microprocessors are classified as being either

RISC (reduced instruction set computer) or CISC (complex instruction set computer) will discuss RISC and

CISC later in this Chapter.

Figure 2.1: Typical Microprocessor Block diagram

The microprocessor system can be divided into two categories: the microprocessor based computer for

general purpose and microprocessor based system for dedicated purpose as defined in sections 2.3 and

2.4, respectively.

2.3 INTRODUCTION TO MICROPROCESSOR BASED SYSTEM

To perform a function or useful task we have to form a system by using microprocessor as a CPU and

interfacing memory, input and output devices to it. A system designed using a microprocessor as its CPU

is called a microcomputer.

The Microprocessor based system (single board microcomputer) consists of a microprocessor as CPU,

semiconductor memories like the ROM/EPROM and the RAM, input device, output device and interfacing

devices. The memories, input device, output device and interfacing devices are called peripherals. The

popular input devices are keyboard and compact disk (CD) and the output devices are printer, LED/LCD

displays, CRT monitor, etc. Address bus Data bus Data bus Control bus

Figure 2.2: A typical Architecture of the Microprocessor based Computer system

The above block diagram (figure 2.2) shows the organization of a microprocessor based system. In this

system, the microprocessor is the master and all other peripherals are slaves. The master controls all the

peripherals and initiates all operations.

The work done by the processor can be classified into the following three groups.

Microprocessor or CPU

PC

Control and Timing unit

ALU

Registers

Instruction

Decoder

Input/output Port/Device (Peripherals)

ADC/DAC

A0-An-1

Microprocessor

(CPU)

D0-Dn-1 I/OW I/OR MW MR

ROM RAM Outside Real World (Analog) To/From

16

1. Work done internal to the processor

2. Work done external to the processor

3. Operations initiated by the slaves or peripherals.

The work done internal to the processor is addition, subtraction, logical operations, data transfer

operations, etc. The work done external to the processor are reading/writing the memory and

reading/writing the I/O devices or the peripherals. If the peripheral requires the attention of the master

then it can interrupt the master and initiate an operation. The microprocessor is the master, which

controls all the activities of the system.

To perform a specific job or task, the microprocessor has to execute a program stored in memory. The

program consists of a set of instructions. It issues address and control signals and fetches the instruction

and data from memory. The instruction is executed one by one internally to the microprocessor and based

on the result it takes appropriate action.

Buses

The buses are group of lines that carries data, address or control signals.

The CPU or system bus has multiplexed lines, i.e., same lines are used to carry data and address signals.

The CPU and memory interface is provided by de-multiplexing of the multiplexed address/data lines;

generation of the memory chip select signal and additional control signals.

The system bus has separate lines for each signal.

All the slave peripherals in the system are connected to the same system bus. At any time instant

communication takes place between the master and one of the slaves, all other slaves have tri-state logic

and hence normally remain in high impedance state when not in use. Only when the slave is selected it

comes to the normal logic.

Peripheral Devices

1. The EPROM memory is used to store permanent programs and data.

2. The RAM memory is used to store temporary programs and data.

3. The input device is used to enter the program, data and to operate the system.

4. The output device is used for examining the results.

Since, speed of the I/O devices does not match with the speed of processor, an interface device is

provided between the system bus and the I/O devices. Generally I/O devices are slow devices.

Advantages of Microprocessor based system

1. Computational/processing speed is high.

2. Intelligence has been brought to systems, automation in the industrial processes and office

administration.

3. Since the devices are programmable, there is flexibility to alter the system by changing the

software program alone.

4. Less number of components, compact in size, more reliable and low cost.

5. Operation and maintenance are easier.

Disadvantages of Microprocessor based System

1. It has limitations on the size of data.

2. The applications are limited due to the limited physical memory address space.

3. The analog signals cannot be processed directly and digitizing the analog signals introduces errors.

4. The speed of execution is slow (when external access is used) and hence real time applications are

not well performed.

5. Most of the microprocessors do not support floating point operations.

2.4 MICROCONTROLLER (C) The microcontroller is a complete microcomputer system on a single-chip that contains all the components

comprising a controller. Typical microcontrollers include a microcomputer (microprocessor, memory and

I/O port), timers, A/D (analog-to- digital) and D/A (digital to analog) converters, all on a single chip, as

shown in figure 2.3. Unlike a general-purpose computer which is also includes all of these components, a

microcontroller is designed for a very specific task - to control a particular system. A microcontroller is

meant to be more self-contained and independent, and functions as a tiny, dedicated computer. The great

advantage of microcontrollers, as opposed to using larger microprocessors, is that the parts-count and

design costs of the item being controlled, can be kept to a minimum. Now, they are designed using CMOS

(complementary metal oxide semiconductor) technology. The microcontrollers are sometimes called

17

embedded microcontrollers, which just mean that they are part of an embedded system. Microcontrollers

are typically used for dedicated applications or smart machines such as automotive systems, home

appliances, and home entertainment systems. Examples of typical microcontrollers are the Intels 8051, Motorolas 6811, Zilogs Z8 and PIC (peripheral interface controller) 16xx from Microchip Technology.

Figure 2.3: A typical block diagram of a microcontroller with its internal components

Microcontrollers Vs Microprocessors 1. Microprocessors

Targeted for high end of market where performance matters.

High power dissipation.

Almost all instructions are byte handling; only one or two instructions are bit handling in a

microprocessor.

High cost.

Need peripheral devices to work.

Mostly used in microcomputers or General Purpose.

A microprocessor requires an external memory for program/data storage. Instruction execution requires

movement of data from the external memory to the microprocessor or vice versa. Usually,

microprocessors have good computing power and they have higher clock speed to facilitate faster

computation.

2. Microcontrollers

Targeted for low end of market where performance does not matter

Low power dissipation.

Low cost.

Bit handling instructions are in vicinity in microcontroller i.e. Microcontrollers have many bit-

handling instructions, while microprocessor has one or two.

Microprocessor, memory and serial/ parallel ports, all integrated into single chip, that is why its a

complete computer on a chip.

A microcontroller does not require much additional interfacing ICs for operation and it functions as a

standalone system. Mostly used in embedded systems or real time, dedicated systems. The operation of a

microcontroller is multipurpose and application specific. A microcontroller has required on-chip memory

with associated peripherals.

2.5 COMPUTER ARCHITECTURES Some important computer/microprocessor architectures are defined in the following paragraphs:

Complex-instruction-set computer (CISC) was popular in 1970s, since the program memory was

slow, designers tried to improve performance by constructing complex and large instruction set. Each

Instruction

Decoder

RTC

Microcontroller

(Single IC)

Timer and counter A/D and D/A converter

Microcomputer

Microprocessor (CPU)

Control and Timing unit

ALU

Registers

I/O Ports Memory (ROM and RAM)

18

complex instruction took several clock cycles, while data flow path control words for each clock cycle were

stored in a much faster micro program memory as shown in figure 2.4. The concept of micro programming

allowed for emulation of arbitrary instruction sets and creation of specialized instructions, while speeding

up the execution. It is difficult to pipeline compared to RISC. Large instruction set helps assembly

language programmers by providing flexibility to write effective and short program. CISC processor

support many addressing modes for the memory access and data transfer instructions. The Intel

8085/80X86, Motorolas 68000 microprocessor are based on CISC.

Figure 2.4: The CISC architecture

Reduced-instruction-set computer (RISC) became popular in late 1980s by eliminating complex

instructions and the micro program memory. The RISC architecture maximizes speed by reducing clock

cycles per instruction and makes it easier to implement pipelining. All instructions in a RISC are simple

and execute in one clock cycle allowing Data flow path to be efficiently pipelined in few pipelined stages.

The micro program memory was replaced with micro instruction decoding stage that followed the

instruction fetch from Program Memory as shown in figure 2.5. Since instructions are simpler, a RISC

needs approximately two instructions for each complex instruction and, therefore, the size of the Program

Memory is approximately doubled. However, the Fetch- Decode-Execute-Store pipeline of the whole

processor improved the execution speed several times. Power PC and PIC microcontroller are the example

of RISC architecture. Intels 80X86 Pentium microprocessors families are CISC based, although RISC type functionality has been incorporated into Pentium CPUs. Sun Microsystemss SPARC microprocessor, MIPS R 2000, R 3000 and R 4000 families dominate the RISC end of the market. However, Digital signal

processors are in wide used in Motorolas Power PC, G4, Intels i860, and analog devices INCs. In the PC/workstation market, Apple computers and Sun employs RISC microprocessors as their choice of CPU.

Figure2.5: The RISC architecture

Table 2.1: CISC versus RISC architecture

CISC (Complex Instruction Set Computer) RISC (Reduced Instruction Set Computer ) Large Instruction set Compact Instruction set

Complex, powerful instruction Simple hard wired machine code and control Unit

Instructions sub-commands micro-coded in on board ROM Pipelining of instructions

Compact and versatile register set Numerous registers

Numerous memory addressing operations for operands Compiler and IC developed simultaneously

2.6 MEMORY ARCHITECTURE

Von - Neumann or Princeton Memory Architecture

Instruction pointer

PROGRAM

MEMORY

(Instructions)

Instruction register

DATA

MEMORY

Timing and

control for data

flow path

Instruction

decoder

Instruction

Pointer (PC)

PROGRAM

MEMORY

(Instructions)

Microinstruction generator (1 instruction = m micro instruction)

Micro-program

memory

(Micro-instruction)

DATA

MEMORY

Timing and

control for data

flow path

Micro-

instruction

decoder

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The Von Neumann Architecture is named after the mathematician and early computer scientist John

Von Neumann. The Von Neumann machines have shared signals and memory for code and data. Thus, the

program can be easily modified by itself since it is stored in read-write memory. There are no separate

instructions to provide separate control signals for data transfer from/to program and data memory as

shown in figure 2.6. For example, the 8085/86 microprocessors.

Both memories share same address and data lines

Figure 2.6: The von-Neumann memory architecture

In Harvard Memory Architecture (shown in figure 2.7), there are separate memories for program and

data with their distinct address and data bus. Both memory organizations have separate control signal as

separate instructions are used for data transfer from/to program and data memory. It is possible to access

program memory and data memory simultaneously. Microcontrollers are characterized by having small

amounts of program (flash memory) and data (SRAM) memory, with no cache, and take advantage of the

Harvard architecture to speed processing by concurrent instruction and data access. The separate storage

means the program and data memories can have different bit depths, for example using 16-bit wide

instructions (in program memory) and 8-bit wide data (in data memory). They also mean that instruction

pre-fetch can be performed in parallel with other activities. Examples include, the AVR by Atmel Corp,

the PIC by Microchip Technology, Inc. , Intel 8051 microcontroller series and the ARM Cortex-M3

processor (not all ARM chips have Harvard architecture).

Both memories use different address and data lines

Figure 2.7: Harvard memory architecture

Princeton versus Harvard memory Architecture Many years ago, in the late 1940's, the US Government asked Harvard and Princeton universities to come

up with a computer architecture to be used in computing distances of Naval artillery shell for defense

applications. Princeton suggested computer architecture with a single memory interface. It is also known

as Von Neumann architecture after the name of the chief scientist of the project in Princeton University

John Von Neumann (1903 1957 Born in Budapest, Hungary). Harvard suggested a computer with two different memory interfaces, one for the data / variables and the

other for program / instructions. Although Princeton architecture was accepted for simplicity and ease of

implementation, Harvard architecture became popular later, due to the parallelism of instruction

execution.

The Von Neumann architectures CPU can be either reading an instruction Op-code from program memory or reading/writing a data from/to the data memory. Both reading and writing operation cannot occur at

the same time since the instructions and data use the same bus system. On the other hand, the CPU with

Harvard architecture can both read an instruction op-code from program memory and perform a data

memory access at the same time, even without a cache. A Harvard architecture computer can thus be

faster for a given circuit complexity because instruction fetches and data access do not contend for a

single memory path way. Also, a Harvard architecture machine has distinct code for instruction and data

address spaces: instruction address zero is not the same as data address zero. Instruction address zero

might identify a 16- bit value, while data address zero might indicate an 8- bit byte that is not part of that

twenty-four bit value.

2.7 THE 8, 16 AND 32-BIT MICROCONTROLLERS

The 8-Bit Microcontroller

Program and Data Memory

CPU

Program Memory

CPU

Data Memory

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When the ALU performs arithmetic and logical operations on a byte (8-bits) at an instruction, the

microcontroller is an 8-bit microcontroller. The internal bus width of 8-bit microcontroller is of 8-bit.

Examples of 8-bit microcontrollers are Intel 8051 family and Motorola MC68HC11 family.


When the ALU performs arithmetic and logical operations on a word (16-bits) at an instruction, the


Examples of 16-bit microcontrollers are Intel 8096 family and Motorola MC68HC12 and MC68332 families.

The performance and computing capability of 16 bit microcontrollers are enhanced with greater precision

as compared to the 8-bit microcontrollers.


When the ALU performs arithmetic and logical operations on a double word (32- bits) at an instruction, the


Examples of 32-bit microcontrollers are Intel 80960 family and Motorola M683xx and Intel/Atmel 251

family. The performance and computing capability of 32 bit microcontrollers are enhanced with greater

precision as compared to the 16-bit microcontrollers.

REVIEW QUESTIONS 1. Why do computers use the binary number system instead of the decimal number system? 2. Differentiate Hardware and Software? 3. What are the RAM and ROM? 4. Why is RAM called volatile memory? 5. Why synchronous digital circuit needs a clock signal? 6. What is the function of Bus? 7. What do you mean by instruction and instruction set? 8. What is a Microprocessor? 9. What is the difference between a Microprocessor and a Microcomputer? 10. Differentiate between microprocessors and microcontroller in one line. 11. Define bit, byte, nibble and word. 12. Which type of memory architecture of the 8051 has? 13. What does it mean by embedded system? 14. What is the difference between microprocessor and CPU? 15. Compare RISC and CISC. 16. Differentiate Von-neumann and Harvard memory architecture. 17. Draw the typical block diagram of a microprocessor, Microcomputer and microcontroller. 18. What do you mean by the power of a Microprocessor? Mention the Architectural Parameters to distinguish

between Microprocessors. 19. Explain the organization of microprocessor based system with its block diagram. 20. Give at least three examples for embedded system. 21. What is the advantage of separate data and program memory (Harvard memory architecture)?

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CHAPTER-3 INTRODUCTION TO MICROCONTROLLER, EMBEDDED PROCESSOR AND SYSTEM

Even though often nearly invisible, embedded systems are everywhere. Embedded systems are present in

many industries, including industrial automation, defense, transportation, our home and aerospace. For

example, NASAs Mars Path Finder, ISROs Mars Orbiter mission, missile guidance system, electronic appliances, and the automobile all contain numerous embedded systems. Every day, people throughout

the world use embedded systems without even knowing it. In fact, the embedded systems invisibility is its

very beauty: users reap the advantages without having to understand the intricacies of the technology.

Remarkably adaptable and versatile, embedded systems can be found at home, at work, and even in

recreational devices. Indeed, it is difficult to find a segment of daily life that does not involve embedded

systems in some way.

INTRODUCTION TO MICROCONTROLLER

Microcontroller is a programmable digital processor with necessary peripherals. In other words, we can

say that a microcontroller is an entire computer manufactured on a single chip. Both microcontrollers and

microprocessors are complex sequential digital circuits meant to carry out job according to the program /

instructions.

Microcontrollers are usually dedicated devices embedded within an application. For example,

microcontrollers are used as engine controllers in automobiles and as exposure and focus controllers in

cameras. In order to serve these applications, they have a high concentration of on-chip facilities such as

serial ports, parallel input-output ports, timers, counters, interrupt control, analog-to-digital converters,

random access memory, read only memory, etc. The I/O, memory, and on-chip peripherals of a

microcontroller are selected depending on the specifics of the target application. Since microcontrollers are

powerful digital processors, the degree of control and programmability they provide significantly enhances

the effectiveness of the application.

Embedded control applications also distinguish the microcontroller from its relative, the general-purpose

microprocessor. Embedded systems often require real-time operation and multitasking capabilities. Real-

time operation refers to the fact that the embedded controller must be able to receive and process the

signals from its environment as they are received. That is, the environment (temperature of a furnace)

must not wait for the controller to become available. Similarly, the controller must perform fast enough to

output control signals to its environment when they are needed. Again, the environment must not wait for

the controller.

EMBEDDED PROCESSOR AND APPLICATION AWARENESS

The processors found in common personal computers (PC) are general-purpose or universal processors

such as Intels x86, Power PC microprocessor, AMD processor etc. They are complex in design because these processors provide a full scale of features and a wide spectrum of functionalities.

They are designed to be suitable for a variety of applications. The systems using these universal

processors are programmed with a multitude of applications. For example, modern processors have a

built-in memory management unit (MMU) to provide memory protection and virtual memory for

multitasking-capable, general-purpose operating systems. These universal processors have advanced

cache logic. Many of these processors have a built-in math co-processor capable of performing fast

floating-point operations. These processors provide interfaces to support a variety of external peripheral

devices. These processors result in large power consumption, heat production, and size. The complexity

means these processors are also expensive to fabricate. In the early days, embedded systems were

commonly built using general-purpose processors.

Because of the great improvement in advancements made in microprocessor technology in recent years,

embedded systems are increasingly being built using embedded processors instead of general-purpose

processors. These embedded processors are special-purpose processors designed for a specific class of

applications. The key is application awareness, i.e., knowing the nature of the applications and meeting

the requirement for those applications that it is designed to run.

One class of embedded processors focuses on size, power consumption, and price. Therefore, some

embedded processors are limited in functionality, i.e., a processor is good enough for the class of

applications for which it was designed but is likely inadequate for other classes of applications. This is one

reason why many embedded processors do not have fast CPU speeds. For example, the processor chosen

for a personal digital assistant (PDA) device does not have a floating-point co-processor because floating-

point operations are either not needed or software emulation is sufficient. The processor might have a 16-

bit addressing architecture instead of 32-bit, due to its limited memory storage capacity. It might have a

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200MHz CPU speed because the majority of the applications are interactive and display-intensive, rather

than computation-intensive. This class of embedded processors is small because the overall PDA device is

slim and fits in the palm of our hand. The limited functionality means reduced power consumption and

long-lasting battery life. The smaller size reduces the overall cost of processor fabrication.

On the other hand, another class of embedded processors focuses on performance. These embedded

processors are powerful and packed with advanced chip-design technologies, such as advanced pipeline

and parallel processing architecture. These processors are designed to satisfy those applications with

intensive computing requirements not achievable with general-purpose processors. An emerging class of

highly specialized and high-performance embedded processors includes network processors developed for

the network equipment and telecommunications industry. Overall, system and application speeds are the

main concerns.

Yet another class of embedded processors focuses on all four requirements performance, size, power

consumption, and price. Take, for example, the embedded digital signal processor (DSP) used in cell

phones. Real-time voice communication involves digital signal processing and cannot tolerate delays. A

DSP has specialized arithmetic units, optimized design in the memory, and addressing and bus

architectures with multiprocessing capability that allow the DSP to perform complex calculations extremely

fast in real time. A DSP outperforms a general-purpose processor running at the same clock speed many

times over comes to digital signal processing. These reasons are why DSPs, instead of general-purpose

processors, are chosen for cell phone designs. Even though DSPs are incredibly fast and powerful

embedded processors, they are reasonably priced, which keeps the overall prices of cell phones

competitive. The battery from which the DSP draws power lasts for hours and hours.

System-on-a-chip (SoC) processors are especially attractive for embedded systems. The SoC processor is

comprised of a CPU core with built-in peripheral modules, such as a programmable general-purpose timer,

programmable interrupt controller, DMA controller, and possibly Ethernet interfaces. Such a self-contained

design allows these embedded processors to be used to build a variety of embedded applications without

needing additional external peripheral devices, again reducing the overall cost and size of the final

product. Sometimes a gray area exists when using processor type to differentiate between embedded and

non-embedded systems. It is worth noting that, in large-scale, high-performance embedded systems; the

choice between embedded processors and universal microprocessors is a difficult one.

SELECTING THE RIGHT MICROCONTROLLER UNIT

What criteria

Microcontrollers and Embedded Systems

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