This presentation contains basic understanding of assembly language programming.This presentation does not contain programs of assembly language.

1. ASSEMBLY
LANGUAGE
PROGRAMMING

2. Why we use Assembly Language?
 We use it for better understanding of interaction
between hardware and software and vice versa.
 We use it for optimization of processing time.
 It is used for embedded programming.

3. Origin of Assembly:-
 The word “assembly” comes from the point that in
older computers,every part of computer is
programmed and programmers assemble the code
of all parts and then compile it for doing some
specific task.

4. What is Assembly Language?
 It is a low level computer programming language, in
which mnemonics are used.
 For e.g. :- ADD,SUB,MOV etc.

5. Why we use Registers?
CPU
Hard disk RAM Cache CPURegisters

6. What is Register?
 Fastest storage area or location (for quickly
accessing by CPU)
 Derived from register which means record or
collection.
 Intel 4004 in 1971,registers were first used.

7. Types of Registers(General Purpose):-
1. Accumulator Register:-
Used for input and output operations basically. Also
used for mathematical and logical operations.
A=8 bits.
Ax=16 bits.
Eax=32 bits.
Rax=64 bits.
2. Base Register:-
Holds addresses of data present in the RAM.
B=8 bits.
Bx=16 bits.
EBx=32 bits.
RBx=64 bits.

8. Types of Registers(General Purpose):-
3. Counter Register:-
Used for counting or loop instructions.
C=8 bits.
Cx=16 bits.
ECx=32 bits.
RCx=64 bits.
4. Data Register:-
Holds data for output.
D=8 bits.
Dx=16 bits.
EDx=32 bits.
RDx=64 bits.

9. Types of Registers(Segment Registers):-
5. Code Segment:-
Hold address of code segment which is in RAM.
6. Data Segment:-
Holds address of data segment.
7. Stack Segment:-
Holds address of stack segment.
8. Extra Segment:-
Holds address extra code in the code segment.

10. Types of Registers(Index Registers):-
9. Source Index:-
Points to the source address.
10. Destination Index:-
Points to the destination operand.

11. Types of Registers(Special Purpose):-
9. Stack Pointer:-
Points the current top of stack.
10. Instruction Pointer:-
Holds the next instruction.
11. Flag Register:-
Hold current status of program.
12. Base pointer:-
Points base of top of stack.

12. Addressing Modes:-
 Ways to access data or How to access data from address.
For e.g:-
2+5
1. Register addressing:-
If both operands are assigned to a register.
E.g:- Add dl,bl
2. Immediate addressing:-
If one operand is assigned to a register and other is constant.
E.g:-Add dl,2
3. Memory addressing:-
Access static data directly from RAM.
E.g:-Add dl,address
Operands
Opcode

13. Data Transfer Instruction & Service Routine:-
 How data comes to a register.
MOV Dl,2
For Printing 2
MOV Ah,2
 Some service routines:-
1=input a character with echo.
2=output/print a single character.
8=input characters without echo.
9=Print string
4ch=Exit.
Service Routine

14. Interrupt:-
 Stop the current program and allow microprocessor to access hardware
to take input or give output.
For e.g:-
INT 21H=Interrupt for text handling
INT 20H=Interrupt for Video/Graphics handling.
For output:-
Mov ah,2
INT 21H
For input:-
Mov ah,1
INT 21H

15. ASCII:-
 Character encoding scheme.
 American standards association.
 1963.
A=65 to Z=90
A=91 to Z=122
0=48
Nextline =10
Carriage return=13.

16. Structure of Program in Assembly?
 Dosseg Manages the arrangements of segments of a
program.
 .model small (Click to understand).
model directive  How much space a program will reserve in
RAM.
 .stack 100h
stack segment directive  Specifies storage for stack.
 .data
data segment directive  Variables are defined here.
 .code
code segment directive Instructions
 Main proc
proc can be any name.
 Main endp
 End main

17. Model sizes….
Ram
Code + data<=64kbtiny
Code<=64kb , data<=64kb small
Code<=Any size , data<=64kb medium
Code<=64kb ,data<=any size compact
Code<=any size , data<=any size large
Code<=any size , data<=any size Huge
data
Code
Stack

18. General Rules for Assembly:-
1. Both operands must be of same size.
Mov Ax,Bl illegal
Mov Al,Bl legal
2. Both operands can not be memory operands simultaneously.
Mov i,j illegal
Mov Ax,j legal
3. First operand can not be an immediate value.
Mov 2,Ax illegal
Mov Ax,2 legal

19. Variables, Data types, Offset and LEA:-
 Data type=Data size
.Data
Note:-Don’t use reserved keywords like add,sub,mov etc.
Different data sizes:-
Variable Name Data Size Value
Var1 Db 49
Var2 Db ‘1’
Var3 Dw ‘12345$’
DB Define Byte 1 byte,8 bits
DW Define Word 2 Bytes,16bits
DD Define double word 4 bytes,32bits
DQ Define Quad word 7 bytes,64bits
DT Define ten bytes 10 bytes,80 bits
$ for terminating string

20. Continued…
 In code segment, we have to follow some steps to access the
data elements. Below is shown:-
1. We need the address of data segment and address contains
16 bits so we need 16 bit register to hold that address.
.code
Mov ax, @data
2. We need to access data from any variable so we need heap
memory(Fast access to data from any variable).So we need
“Ds” register which is way to create heap memory. So ax
which contains address of data should be moved to ds
register for address contained by ax to be converted to heap
memory .
Mov ds,ax.
Accumulator used for input and output of data

21. Continued…
 If we have an string and wanted to move it to a
register we use offset(which holds the beginning
address of variable) or lea(an in directed instruction
used as a pointer in which first variable points to the
address of second variable).
 As follows
mov dx,offset var3
Or
Lea dx,var3 .