with ASSEMBLY LANGUAGE

ComputerSystemOrganization

GROUP OF REGISTERS

General Purpose Registers

Data registers

1. AX (accumulator register)

2. BX (base register)

3. CX (count register)

4. DX(data register)

Arithmetic operations: addition, subtraction, multiplication, division

Address in data memory

Loop operations

Data storage

Segment registers

Holds starting addresses of a computer system

1. CS (code segment register)

2. SS (stack segment register)

3. DS (data segment register)

4. ES(extra segment register)

Points to the segment that holds the program currently being executed

Points to the current stack segment

Points to the current data segment, which usually holds variables

Usually used in string operations

Point and index registers

1. SP (stack pointer)

2. BP (base pointer)

3. SI (source index)

4. DI (destination index)

Offset of stack segment

Offset of stack segment

Offset of data segment

Offset of data segment

ASsembly language

Some characteristics

Low level language

Platform dependent: not portable

Works directly with microprocessors

Why assembly language?

Makes you a better programmerSome problems can only be resolved using assembly language

The only programming language that can talk directly to the hardware

The only programming language that can talk directly to the hardware

Each statement in assembly can either be:

1. Assembly Language Instructions

2. Assembler directives

Tells the machine what to do

Tells the assembler what to do(with your instructions and data)

Constants in source statements:

binary Sequence of numbers 0s and 1s followed by B

decimal

hexadecimal

character

Sequence of numbers 0 to 9, with or without letter D

sequence of digits 0 through 9 and letters A to F followed by H (first character must be 0 to 9)

string of letters, numbers or symbols enclosed in single or double quotes

1111B1011B

100D76

1ah41h

‘A’

“I am a programmer”

assembly instructions can have up to 4 fields:

Format: [label]Mnemonic[operand][;comments]

NOTE:only the mnemonic field is always required

Label field:

Assigns name to an assembly instruction

Maximum of 31 characters and must with a colon (:)

Can be A to Z(a to z), digits 0 to 9, and special characters like underscore(_)

Cannot begin with a digitRegisters(AX, BX, CX, DX, etc.) can not be used as labels

mnemonic field:

Contains 2 to characters acronym for assembly language instruction

operand field:

Tells the machine where to find data that it is to operate on

In two-operand operations, the first letter is the destination and the second letter is the source

comment field:

Describes the statements in the source program

Starts with semi colon (;)

Assembler directives can have 4 fields:

Format: [name]directive[operand][;comments]

NOTE:Only the directive field is always required

END