; multi-segment executable file template.

data segment
    ; add your data here!
    pkey db "press any key...$"
ends

stack segment
    dw   128  dup(0)
ends

code segment
start:
; set segment registers:
    mov ax, data
    mov ds, ax
    mov es, ax

    ; add your code here 
    
    
    mov al, - 1
    
    mov ah, 1
    
    
    
    cmp al,  ah
    
    
    
            
    lea dx, pkey
    mov ah, 9
    int 21h        ; output string at ds:dx
    
    ; wait for any key....    
    mov ah, 1
    int 21h
    
    mov ax, 4c00h ; exit to operating system.
    int 21h    
ends

end start ; set entry point and stop the assembler.

Assembly Online Compiler

Write, Run & Share Assembly code online using OneCompiler's Assembly online compiler for free. It's one of the robust, feature-rich online compilers for Assembly language. Getting started with the OneCompiler's Assembly compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as Assembly and start coding.

About Assembly

Assembly language(asm) is a low-level programming language, where the language instructions will be more similar to machine code instructions.

Every assembler may have it's own assembly language designed for a specific computers or an operating system.

Assembly language requires less execution time and memory. It is more helful for direct hardware manipulation, real-time critical applications. It is used in device drivers, low-level embedded systems etc.

Syntax help

Assembly language usually consists of three sections,

  1. Data section

    To initialize variables and constants, buffer size these values doesn't change at runtime.

  2. bss section

    To declare variables

  3. text section

    _start specifies the starting of this section where the actually code is written.

Variables

There are various define directives to allocate space for variables for both initialized and uninitialized data.

1. To allocate storage space to Initialized data

Syntax

variable-name    define-directive    initial-value
Define DirectiveDescriptionAllocated Space
DBDefine Byte1 byte
DWDefine Word2 bytes
DDDefine Doubleword4 bytes
DQDefine Quadword8 bytes
DTDefine Ten Bytes10 bytes

2. To allocate storage space to un-initialized data

Define DirectiveDescription
RESBReserve a Byte
RESWReserve a Word
RESDReserve a Doubleword
RESQReserve a Quadword
RESTReserve a Ten Bytes

Constants

Constants can be defined using

1. equ

  • To define numeric constants
CONSTANT_NAME EQU regular-exp or value

2. %assign

  • To define numeric constants.
%assign constant_name value

3. %define

  • To define numeric or string constants.
%define constant_name value

Loops

Loops are used to iterate a set of statements for a specific number of times.

mov ECX,n
L1:
;<loop body>
loop L1

where n specifies the no of times loops should iterate.

Procedures

Procedure is a sub-routine which contains set of statements. Usually procedures are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

procedure_name:
   ;procedure body
   ret