This document discusses assembly language programming. It provides an overview of assembly language, how it relates to machine language, and how assemblers are used to convert assembly code into machine-readable object code. It also describes the basic components of assembly language instructions, including opcodes and operands, and different addressing modes for specifying operands in memory or registers. Common addressing modes like immediate, register, direct, register indirect, and based indexed modes are defined through examples.

2. Assembly language Programming
 Low level language.
 Depends on computer architecture.
 Compiler converts high level language into machine language.
 Assembler converts the ALP into machine language.
 Machine language instructions contain only 0’s and 1’s.
 Assembly language contain Mnemonics.
 To study the behavior of particular architecture
Machine Language Assembly Language
B9 04 00 MOV CX,0004
B9 10 00 MOV CX,0010

3. Instructions
 An instruction is divided in to two fields.
 One field – Operation code (opcode)
 Another field – Operands
 An instruction contains an opcode and one or more operand
 Mostly instructions contain only one or two operand.
 Instruction size varies from 1 to 6 byte.
Assembly Language
MOV CX,0004
MOV  Op-code
0004,CX  Operands
ADD AX,BX
Opcode
Instruction
Operand

4. Addressing Modes
 The way in which operands are specified
 The operand may be mentioned directly or specified in register/memory.
 7 types of Data Addressing Mode.

5. Data Addressing Modes
 Immediate
 Direct
 Register
 Register Indirect
 Register Relative
 Based Indexed
 Relative Based Indexed

6.  One of the operand is mentioned directly.
 Data is available as a part of instruction.
 Data is 8 0r 16 bit long.
 No memory reference is needed to fetch data
Immediate Addressing Modes

7. Immediate Mode :Eg.
Example 1 : MOV CL, 03H
03 – 8 bit immediate source operand
CL – 8 bit register destination operand
Example 2: ADD AX, 0525H
0525 – 16 bit immediate source operand
AX – 16 bit register destination operand.

8. Register Addressing Mode
 Both the operands are in registers
 No memory access
 Limited number of registers
 Very small address field is needed to address registers.
 Shorter instructions
Register Address
ES 00
CS 01
SS 10
DS 11

9. Example
Examples : 16 bit register instruction
MOV AX,BX
ADD AX,DI
8 bit register instructions
MOV CL,DL
ADD AL,CL

10. Direct addressing Modes
 One or both the operands are in memory.
 Operand in memory is specified through its effective address.
 Default Segment register – DS
 Data in that location will be used for specified operation.
 If the instruction contain stack operation, segment register will
be SS.

11. Example
MOV CX, [0400]
[DS] = 3050
PA : 30500+0400 = 30540.
[30540]  CL
[30541] CH

12. Register indirect Mode
 EA of operand(s) is/are specified in register.
 Physical address is computed using segment register and EA .
 Data in the physical address is an operand

13. Example
 Example 1 : MOV AX, [BX]
[DS] = 5004, [BX] = 0020, PA=50060.
50060 contain 0015H
0015H is moved to memory AX
 Example 2: MOV [BX],[AX]
Source and destination address is calculated by AX and BX content
respectively .
Then content of source address is moved to destination address

14. Register Relative
 Effective address = [ Base/pointer register] + 8 or 16 bit
displacement
 Base/Pointer register : BX or BP or SI or DI

15. Example
 MOV AX, 10[BP]
 [BP] = 0105 , [DS] = 2020
 P.A = 20200 + 0105 + 10 = 20315
 Content of memory address 20315 is moved to AX

16. Based Indexed MODE
 Effective address = [Base register] + [Index register]
 Base register  BX or BP
 Index register  SI or DI

17. Example
 MOV AX,[BX][SI]
[BX] = 1500 [SI] = 0020 [DS] = 2020
P.A of source : 20200 + 1500 + 0020 = 21720
Content of 21720 is moved to AX

18. Relative Based Indexed
 Effective address = [Base register] + [Index register]
+ 8 or 16 bit displacement

19. Example
1. MOV CX,1010[BX][SI]
[BX] = 102B [SI] = 0003 [DS] = 2020
PA = 20200 + 102B + 0008 + 1010 = 2223E
Content of memory address 2223E is moved to CX
2.MOV 1010[BX][SI], CX

20. Which Mode is fastest? Why?
 Register addressing mode
 Direct addressing modes require more bits to represent address of operand
 Memory reference require 20 bits
 Limited number of registers
 Very small address field needed
 Shorter instructions
 Faster instruction fetch
 Register reference require only 2 or 3 bits .

21. Problem
Given that
[BP] = 5000 [SI] = 0005 [DI]=0100 [DS] = 1000
[6000] = 520A [6005] = 5402 [6100] = 0003 [6015]=065B
[6110] = 003E
[5000] = 5505 [5100] = FB05 [5005] = 060B
After the following instructions are executed, What will be the value
of registers AX,BX,CX,DX ? DS is a segment register for all instructions.
MOV AX,[BP]
MOV DX, [5100]
MOV BX,5[BP]
MOV CX,[BP][DI]

22. ALP Program
MOV AX,4343
MOV BX,1111
ADD AX,BX
MOV [2000H],AX
HLT
Note:
HLT – Halt the process.
Indicate end of the program

23. ALP for different addressing modes
 Immediate mode
MOV AX, 200
ADD AX,300
MOV [2000],AX
HLT
 Register mode
MOV BX,500
MOV AX,200
ADD AX,BX
MOV [5000],AX
HLT

24.  Direct mode
MOV AX,[5000]
ADD AX,[5002]
MOV AX,[5004]
HLT
 Register indirect mode
MOV BX,5000
MOV DX, 5002
ADD [DX],[BX]
MOV [5004],AX
HLT

25. Register Relative mode
MOV BX,4990
MOV AX,300
ADD AX,10[BX]
MOV [5002],AX
HLT
Based indexed mode
MOV AX,300
MOV BX,5000
MOV SI,5
ADD AX,[BX][SI]
MOV [5002],AX
HLT

26.  Relative Based indexed
MOV BX,5000
MOV SI,5
MOV CX,5[BX][SI]
MOV AX,300
ADD AX,CX
MOV [5012],AX
HLT

27. Steps
 Menu display – A,D,F,I,M,P,T,U
 Enter A - Assembly
 Enter program
 Menu display – D input location
 Input data in memory
 Execute using Go command
 Menu display – D output location