Assembly language is converted into executable machine code by a utility program referred to as an assembler like NASM, MASM etc. Audience.
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TUTORIALS POINT Simply Easy Learning ABOUT THE TUTORIAL Assembly language is a low – level programming language for a computer, or other programmable device specific to a particular computer architecture in contrast to most high – level programming languages, which are generally portable across multiple systems. Assembly language is converted into executable machine code by a utility program referred to as an assembler like NASM, MASM etc . This tutorial has been designed for software programmers with a need to understand the Assembly programming language starting from scratch. This tutorial will give you enough understanding on Assembly programming language from where you can take yourself at higher level of expertise. Before proceeding with this tutorial you should have a basic understanding of Computer Programming terminologies. A basic understanding of any of the programming languages will help you in understanding the Assembly programming concepts and move fast on the learning track.

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TUTORIALS POINT Simply Easy Learning T able of Content Assembly Prog ramming Tutorial .. .. 2 Audience .. .. 2 Prerequisites .. .. 2 Copyright & Disclaimer Notice .. 3 Assembly Introduction .. 8 What is Assembly Language? .. .. 8 Advantages of Assembly Language .. 8 Basic Features of PC Hardware .. .. . 9 The Binary Number System .. .. . 9 The Hexadecimal Number System .. .. 9 Binary Arithmetic .. .. . 10 Addressing Data in Memory .. .. .. 11 Assembly Environment Setup .. . 13 Installing NASM .. .. 13 Assembly Basic Syntax .. .. 15 The data Section .. .. . 15 The bss Section .. .. .. 15 The text section .. .. 15 Comments .. .. .. 15 Assembly Language Statements .. 16 Syntax of Assembly Language Statements .. .. 16 The Hello World Program in Assembly .. 16 Compiling and Linking an Assembly Program in NASM 17 Assembly Memory Segments .. .. 18 M emory Segments .. .. . 18 Assembly Registers .. . 20 Processor Registers .. .. .. 20 Data Registers .. .. . 20 Pointer Registers .. .. . 21 Index Registers .. .. 21 C ontrol Registers .. .. 22 Segment Registers .. .. . 22 Example: .. .. .. .. 23 Assembly System Calls .. .. 24 Linux System Calls .. .. . 24 Example .. .. .. 25 Addressing Modes .. .. . 27

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TUTORIALS POINT Simply Easy Learning Register Addressing .. .. .. 27 Immediate Addressing .. .. .. 27 Direct Memory Addressing .. .. . 28 Direct – Offset Addressing .. .. . 28 Indirect Memory Addressing .. .. .. 28 The MOV Instruction .. .. . 28 SYNTAX: .. .. .. .. 28 EXAMPLE: .. .. 29 Assembly Variables .. . 31 Allocating Storage Space for Initia lized Data .. .. 31 Allocating Storage Space for Uninitialized Data .. . 32 Multiple Definitions .. .. . 32 Multiple Initializations .. .. 33 Assembly Constants .. 34 The EQU Directive .. .. . 34 Example: .. .. .. .. 34 The %assign Directive .. .. .. 35 The %define Directive .. .. .. 35 Arithmetic Instructions .. . 37 SYNTAX: .. .. .. . 37 EXAMPLE: .. .. 37 The DEC Instruction .. .. .. 37 SYNTAX: .. .. .. . 37 EXAMPLE: .. .. 37 The ADD and SUB Instructions .. .. 38 SYNTAX: .. .. .. .. 38 EXAMPLE: .. .. . 38 The MUL/IMUL Instruction .. .. . 40 SYNTAX: .. .. .. .. 40 EXAMPLE: .. .. . 41 EXAMPLE: .. .. 41 The DIV/IDIV Instructions .. .. 42 SYNTAX: .. .. .. . 42 EXAMPLE: .. .. 43 Logical Instructions .. .. 45 The AND Instruction .. .. .. 45 Example: .. .. .. .. 46 The OR Instruction .. .. . 46 Example: .. .. .. .. 47

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TUTORIALS POINT Simply Easy Learning Creating and Opening a File .. .. . 75 Opening an Existing File .. .. . 75 Reading from a File .. .. 75 Writing to a File .. .. 76 Closing a File .. .. 76 Updating a File .. .. . 76 Example: .. .. .. .. 77 Memory Management .. . 79 Example: .. .. .. .. 79

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TUTORIALS POINT Simply Easy Learning Assembly Introduction E ach personal computer has a microprocessor that manages the computer’s arithmetical, logical and control activities. Each family of processors has its own set of instructions for handling various operations like getting input from keyboard, displaying information on screen and performing various other jobs. These set of instr uctions are called ‘machine language instruction’. Processor understands only machine language instructions which are strings of 1s and 0s. However machine language is too obscure and complex for using in software development. So the low level assembly lan guage is designed for a specific family of processors that represents various instructions in symbolic code and a more understandable form. An understanding of assembly language provides knowledge of: Interface of programs with OS, processor and BIOS; Representation of data in memory and other external devices; How processor accesses and executes instruction; How instructions accesses and process data; How a program access external devices. Other advantages of using assembly language are: It requires less memory and execution time; It allows hardware – specific complex jobs in an easier way; It is suitable for time – critical jobs; C HAPTER 1

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TUTORIALS POINT Simply Easy Learning It is most suitable for writing interrupt service routines and other memory resident programs. The main internal hardware of a PC consists of the processor, memory and the registers. The registers are processor components that hold data and address. To execute a program the system copies it from the external device into the internal memory. The processor executes the program instructions. The fundamental unit of computer storage is a bit; it could be on (1) or off (0). A group of nine related bits makes a byte. Eight bits are used for data and the last one is used for parity . According to the rule of parity, number of bits that are on (1) in each byte should always be odd. So the parity bit is used to make the number of bits in a byte odd. If the parity is even, the system assumes that there had been a parity error (though ra re) which might have caused due to hardware fault or electrical disturbance. The processor supports the following data sizes: Word: a 2 – byte data item Doubleword: a 4 – byte (32 bit) data item Quadword: an 8 – byte (64 bit) data item Paragraph: a 16 – byte (128 bit) area Kilobyte: 1024 bytes Megabyte: 1,048,576 bytes Every number system uses positional notation i.e., each position in which a digit is written has a different positional value. Each position is power of the base, which is 2 for binary number system, and these powers begin at 0 and increase by 1. The following table shows the positional values for an 8 – bit binary number, where all bits are set on. Bit value 1 1 1 1 1 1 1 1 Position value as a power of base 2 128 64 32 16 8 4 2 1 Bit number 7 6 5 4 3 2 1 0 The value of a binary number is based on the presence of 1 bits and their positional value. So the value of the given binary number is: 1 + 2 + 4 + 8 +16 + 32 + 64 + 128 = 255, which is same as 2 8 – 1. Hexadecimal number system uses base 16. The digits range from 0 to 15. By convention, the letters A through F is used to represent the hexadecimal digits corresponding to decimal values 10 through 15.

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TUTORIALS POINT Simply Easy Learning Main use of hexadecimal numbers in computing is for abbreviating lengthy binary representations. Basically hexadecimal number system represents a binary data by dividing each byte in half and expressing the value of each half – byte. The following table provides the decimal, binary and hexade cimal equivalents: Decimal number Binary representation Hexadecimal representation 0 0 0 1 1 1 2 10 2 3 11 3 4 100 4 5 101 5 6 110 6 7 111 7 8 1000 8 9 1001 9 10 1010 A 11 1011 B 12 1100 C 13 1101 D 14 1110 E 15 1111 F To convert a binary number to its hexadecimal equivalent, break it into groups of 4 consecutive groups each, starting from the right, and write those groups over the corresponding digits of the hexadecimal number. Example : Binary number 1000 1100 1101 0001 is equivalent to he xadecimal – 8CD1 To convert a hexadecimal number to binary just write each hexadecimal digit into its 4 – digit binary equivalent. Example : Hexadecimal number FAD8 is equivalent to binary – 1111 1010 1101 1000 The following table illustrate s four simple rules for binary addition: (i) (ii) (iii) (iv) 1 0 1 1 1 +0 +0 +1 +1 =0 =1 =10 =11 Rules (iii) and (iv) shows a carry of a 1 – bit into the next left position. Example:

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