Assembler

Assembler:- Assembler is a program that converts assembly language program into
    
machine language.Thus input to an assembler is a program written in assembly language

and the output of program is machine language.

Assembly language:-Assembly language is low level programming language and machine

dependent. It makes use of symbols and mnemonic to represent instructions and address

because of this reason assembly language is also known as symbolic language.

Assembly   language  statements:-

1. Imperative  statements

     2. Declarative  statements  

     3. Assembler  directives  

Imperative  statements:- An imperative statement indicates that what action to be performed

during the execution of assembly language program . Examples of imperative statements

are MOVER , MOVEM , ADD , SUB , MULT etc .

Declarative statements:- Declarative statements are used to declare  a storage space or

declare a constant or variable . There are two declarative statements :  DC  and  DS

DS : - DS stands for declare storage . It reserves blocks of memory.

     Syntax : [ label ]  DS  < constant >

Eample :- A  DS  1  ,  This statement reserves the memory area of  one word and attaches

name A with it.


Example :-  A  DS  100  , this statement reserves memory block of 100 memory words  and

name  A is associated with first word of the block .

DC : - DC stands for declare constant  . It constructs the memry block containing constants.

   Syntax :  [ label ]  DC  <value>

Example :- Two  DC  ' 2'  , This statement constructs a memory words containing value 2

and associates the name Two with it .

Assembler  directives :- Assembler directives direct or instruct the assembler to perform

a particular action during the assembly of the program.

Note : No memory space is reserved for any assembler directives  during the processing of

assembler directives.

List of assemler directives :-

     1. START

    2. END

    3. ORIGIN

   4. EQU

   5. LTORG

   6. USING

   7. DROP

   8. BALR