![Syntax of Assembly Language
Statements
Assembly language statements are entered one statement
per line. Each statement follows the following format −
[label] mnemonic [operands] [;comment]
The fields in the square brackets are optional. A basic
instruction has two parts, the first one is the name of the
instruction (or the mnemonic), which is to be executed,
and the second are the operands or the parameters of
the command.](https://image.slidesharecdn.com/assemblylanguage-221216215100-f3bbcfc1/85/ASSEMBLY-LANGUAGE-pptx-18-320.jpg)
ASSEMBLY LANGUAGE.pptx
- 3. Introduction 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.
- 4. Introduction Each 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 such as getting input from keyboard, displaying information on screen and performing various other jobs. These set of instructions are called 'machine language instructions'.
- 5. Introduction A processor understands only machine language instructions, which are strings of 1's and 0’s. However, machine language is too obscure and complex for using in software development. the low-level assembly language is designed for a specific family of processors that represents various instructions in symbolic code and a more understandable form.
- 6. Advantages of Assembly Language Having an understanding of assembly language makes one aware of − How programs interface with OS, processor, and BIOS; How data is represented in memory and other external devices; How the processor accesses and executes instruction; How instructions access and process data; How a program accesses external devices.
- 7. Advantages of Assembly Language 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; It is most suitable for writing interrupt service routines and other memory resident programs.
- 8. Basic Features of PC Hardware The main internal hardware of a PC consists of processor, memory, and registers. 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) and a group of 8 related bits makes a byte on most of the modern computers.
- 9. Basic Features of PC Hardware 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
- 10. Assembly Language Parts An assembly program can be divided into three sections − The data section, The bss section, and The text section.
- 11. Data section The data section is used for declaring initialized data or constants. This data does not change at runtime. You can declare various constant values, file names, or buffer size, etc., in this section. The syntax for declaring data section is − section.data
- 12. bss section The bss section is used for declaring variables. The syntax for declaring bss section is − section.bss
- 13. Text section The text section is used for keeping the actual code. This section must begin with the declaration global _start, which tells the kernel where the program execution begins. The syntax for declaring text section is − section.text global _start_start:
- 14. Comments Assembly language comment begins with a semicolon (;). It may contain any printable character including blank. It can appear on a line by itself, like − ; This program displays a message on screen or, on the same line along with an instruction, like − add eax, ebx ; adds ebx to eax
- 15. Assembly Language Statements Assembly language programs consist of three types of statements − Executable instructions or instructions, Assembler directives or pseudo-ops, and Macros.
- 16. Assembly Language Statements The executable instructions or simply instructions tell the processor what to do. Each instruction consists of an operation code (opcode). Each executable instruction generates one machine language instruction.
- 17. Assembly Language Statements The assembler directives or pseudo-ops tell the assembler about the various aspects of the assembly process. These are non-executable and do not generate machine language instructions. Macros are basically a text substitution mechanism. .
- 18. Syntax of Assembly Language Statements Assembly language statements are entered one statement per line. Each statement follows the following format − [label] mnemonic [operands] [;comment] The fields in the square brackets are optional. A basic instruction has two parts, the first one is the name of the instruction (or the mnemonic), which is to be executed, and the second are the operands or the parameters of the command.
- 19. Syntax of Assembly Language Statements
- 20. Structure of a NASM Program NASM is line-based. Most programs consist of directives followed by one or more sections. Lines can have an optional label. Most lines have an instruction followed by zero or more operands. This is the project webpage for the Netwide Assembler (NASM), an assembler for the x86 CPU architecture portable to nearly every modern platform, and with code generation for many platforms old and new
- 21. Structure of a NASM Program
- 22. Memory Segments A segmented memory model divides the system memory into groups of independent segments referenced by pointers located in the segment registers. Each segment is used to contain a specific type of data. One segment is used to contain instruction codes, another segment stores the data elements, and a third segment keeps the program stack.
- 23. Memory Segments In the light of the above discussion, we can specify various memory segments as − Data segment − It is represented by .data section and the .bss. The .data section is used to declare the memory region, where data elements are stored for the program. This section cannot be expanded after the data elements are declared, and it remains static throughout the program. The .bss section is also a static memory section that contains buffers for data to be declared later in the program. This buffer memory is zero-filled.
- 24. Memory Segments Code segment − It is represented by .text section. This defines an area in memory that stores the instruction codes. This is also a fixed area. Stack − This segment contains data values passed to functions and procedures within the program.
- 25. TASM Turbo Assembler (sometimes shortened to the name of the executable, TASM) is an assembler for software development published by Borland in 1989. It runs on and produces code for 16- or 32-bit x86 MS-DOS and compatible on Microsoft Windows
- 26. MASM The Microsoft Macro Assembler (MASM) is an x86 assembler that uses the Intel syntax for MS-DOS and Microsoft Windows. Beginning with MASM 8.0, there are two versions of the assembler: One for 16-bit & 32-bit assembly sources, and another for 64-bit sources only.
- 27. Assemblers expect either the original syntax used in the Intel instruction set documentation - the Intel syntax - or the so-called AT&T syntax developed at the AT&T Bell Labs. AT&T uses mov src, dest, Intel uses mov dest, src, amongst other differences.
- 28. Windows assemblers prefer Intel syntax (TASM, MASM), most Linux/UNIX assemblers use AT&T. NASM uses a variant of the Intel syntax. Assemblers have their own syntax for directives affecting the assembly process, macros and comments. These usually differ from assembler to assembler
- 29. QUIZ
- 30. ______________1. What symbol defines Comments in Assembly Language? ______________2. This section is used to declare the memory region, where data elements are stored for the program. ______________3. This defines an area in memory that stores the instruction codes. This is also a fixed area. ______________4. Which part of the assembly language tells the kernel where the program execution begins? ______________5. Which tells the assembler about the various aspects of the assembly process. These are non-executable and do not generate machine language instructions. ______________6. What is the syntax in declaring data section? ______________7. This segment contains data values passed to functions and procedures within the program. ______________8. What is the fundamental unit of computer storage? _____9_______10. Advantages of understanding Assembly language
- 31. 1. Semicolon 2. Data segment 3. Code segment 4. global _start, 5. assembler directives 6. section.data 7. Stack 8. bit How programs interface with OS, processor, and BIOS; How data is represented in memory and other external devices; How the processor accesses and executes instruction; How instructions access and process data; How a program accesses external devices.