Memory Address

• Segment-offset address• Base location (segment) + logical location (offset)• Example:• For 32-bits segment-offset address, 08F1:0100

represents a 20-bits absolute address 09010• 0 8 F 1 (0)• 0000 1000 1111 0001 0000• + 0 1 0 0• 0 9 0 1 0•

Floating-Point Unit• 80-bit Registers

ST(0)

ST(1)

ST(7)

FPU Instruction Pointer

FPU Data Pointer

Tag Register

Control Register

Status Register

48-bit Pointer Register

16-bit Control Register

Opcode Register

DUP Operator

• db 20 dup(0) ; 20 bytes, all equal to zero

• db 20 dup (?) ; 20 un-initialized bytes

• db 4 dup(“ABC”) ; 12 bytes: “ABCABCABCABC”

• db 4096 dup(0);

Assembly Language

• Basic elements

• 1. Constant and expression

• 3

• 3.5

• - 3.5

• 26. E+07

Integer Constants

• 26 decimal

• 1Ah hexadecimal

• 1101b binary

• 36q octal

• 2BH hexadecimal

• 43Q octal

• 36D decimal

• 48d decimal

Constant Expression, Symbolic constants and Character or String Constants

• Constant expression

• 5 26.5 4*20 -3*4/6 -2.301E+04

• A symbolic constant

• rows = 5 columns = 10

• Number = rows * columns

• Character or string constant

• ‘ABC’ ‘X’ “ This is a test” “The dog is black”

Assembly Language Statement

• Consists of :

• 1. A name, an instruction mnemonic, operands, and a comment. It has the following form:

• [name] [mnemonic] [operands] [;comment]

• Example:

• call sub1 ; transfer of control

Names• A name identifies a label, variable, symbolic, or

a keyword.• What can be used as a name:• 1. A… Z a… z• 2. 0-9• 3. ?• 4. _ Underscore• 5. @• 6. $• Length limit----maximum of 247 characters (in

MASM)

Variables and Labels

• 1. A variable is a location in a program’s data area that has been assigned a name.

• Such as: count1 db 50 ; • message db “ Hello world!”, odh, 0ah• 2. Label. If a name appears in the code area of a

program, it is called a label.• Example: • LabelA: mov ax, 0• mov bx, ffh•

Hello World Program• title Hello World Program (hello.asm)• ; This program displays "Hello, world!"• .model small• .stack 100h• .data• message db "Hello, world!",0dh,0ah,'$'• .code• main proc• mov ax,@data• mov ds,ax• mov ah,9• mov dx,offset message• int 21h• mov ax,4C00h• int 21h• main endp• end main

Analyze the Program• .model small ----specify the program’s memory model• For that model we can have:• Tiny--- code + data less than 64k• Samll--- code <=64k, data ,<=64k One code segment and

one data segment• Medium---Data <=64k, code any size. Multiple code

segment, one data segment• Compact---Code <= 64k, data any size. Multiple data

segment, one code segment• Large---Code >64k, data >64k both multiple segment• Huge---Same as the large model, except that individual

variables such as arrays may be large than 64k• Flat--- No segments. 32-bits addresses are used for both

code and data. ***Protected mode only

•

Standard Assembler Directives• end---end of program assembly• endp--- end of procedure• page---Set a page format for the listing file• proc---Begin procedure• title---Title of the listing file• .code--- Mark the beginning of the code

segment• .data---• .model---• .stack---Set the size of the stack segment

Data Allocation Directives

• DB--------------------1 byte

• DW-------------------2

• DD--------------------4

• DF, DP---------------6---define far pointer

• DQ--------------------8 define Quadword

• DT--------------------10 define 10 bytes

Examples• Char1 db ‘A’ ; ASCII char.

• Char2 db “A’ –10 ; expression

• Smallest db –128

• Max_unsign db 255

• Myval db ? Only reserve memory, no initializeers

• List db 10,20,30,40,50

Characters and Integers are one and the same

• Char db ‘A’

• Hex db 41h

• Dec db 65

• Bin db 01000001

• Oct db 101q

Type mix is allowed

• List db 10, 20, 41h, 10011000b

• List2 db 0ah, 29h, ‘a’, 22

Strings

• Cstring db “Good morning”,0

• Pstring db 12, “Good morning”

• Longstring db “This is a long string, that”• db “ clearly is going to take”• db “ several lines to store”,0

Symbolic Constants• Equate directives• They allow constants and literals to be

given symbolic names.

• 1. Equal-Sign Directive (redefinable)• The syntax is: name = expression• Examples: string = ‘XY’• count = 500• minInt = 8000h•

To assign a 32 bits integer---.386 is required

• .386

• maxLong = 7FFFFFFFh ; maximum 32-bit signed value

• minLong = 80000000h ; Minimum 32-bit signed value

• “=“ defined symbols can be redefined any number of times.

Example of Using Directives

• count =5

• mov al , count

• mov dl , al

• count =10

• mov cx , count

• count = 2000

• mov ax, count

EQU and TEXTEQU directives• EQU is not redefinable

• TEXTEQU is redefinable

• Examples: maxint equ 32767; Numeric

• float1 equ <3.1416> ; String

• TEXTEQU syntax:

• name TEXREQU <text>

• name TEXTEQU textmacro

Intel chip Instructions

• 1. MOV---Data transfer instruction

• Instruction format:• MOV reg, reg MOV reg, immed• MOV mem, reg MOV mem, immed• MOV reg, mem

MOV mem16, segreg• MOV reg16, segreg • MOV segreg, immed16• MOV segreg, reg16• *** Flag bits are not affected by MOV instruction

Examples

• .data

• count db 10

• total dw 4126h

• bigVal dd 12345678h

• .code

• mov al, bl

• mov bl, count

• mov count, 26

• mov bl, 1

Examples—cont…• mov dx, cx

• mov bx, 8FE2h

• mov total, 1000h

• mov eax, ebx

• mov edx, bigVal ; 32-bit memory to reg

• ***Pay attention the the fact that operands size must match. Otherwise, the assembler will return an error for any size mismatch.

Example

• .data • count dw 20h ; 20h---here really mean 0020h

• .code• mov al, count; error:

XCHG Instruction

• XCHG reg, reg

• xchg ax, bx

• xchg eax, ebx

• XCHG reg, mem

• xchg ax, value1

• XCHG mem, reg

• xchg value2, cx

Program example• Title Exchange Two Variables (Exchange.asm)• .model small• .stack 100h• .data• Value1 db 0ah• Value2 db 14h• .code• Main proc• Mov ax, @data ; initialize DS register• Mov ds, ax• Mov al, value1• Xchg value2, al• Mov value1, al• Mov ax, 4c00h• Int 21h• Main endp• End main; Question: Why don’t we use xchg value1, value2?

Arithmetic Instructions

• ADD and SUB instructions

• ADD reg, reg

• ADD mem, reg

• ADD reg, mem

• ADD reg, immed

• ADD mem, immed

• ADD accum, immed• Flag O D I S Z A P C

• SUB has the similar instruction format

* * * * * *

Examples• Mov ax, 10

• Sub ax, 10 ; AX=0, ZF =1

• Mov bx, 1

• Sub bx, 2 ; BC = FFFF, SF = 1

• Mov ax, 0FFh

• Add al, 1 ; AL = 00 , CF = 1

Basic Operand Types• There are three basic types of operands:

• 1. Immediate----a constant

• 2. Register-------one of the CPU’s register

• 3. Memory---a reference to a mem.Location

• There are six different types of memory operands:

• Direct, direct-offset, register-indirect

• Indexed, base-indexed, and base-indexed with displacement

Example

• mov ax, [si] --- this is called register-indirect

• Here si register hold the beginning address for a list of numbers.

• The first number in the address will be moved to al and the second number will be moved into ah.

Immediate operands, Direct Operands, and Direct-Offset operands

• 1. Immediate operands:

• Mov al, 10 ; ----a number

• Mov eax, 12345678h ; ---a 4-byte number

• Mov dl, ‘X’ ; --- a character

• Mov ax, (40 *50) ; arithmetic expression

Direct Operands• .data

• Count db 20

• Wordlist dw 1000h, 2000h

• LongVal dd 11223344h

• .code

• Mov al, Count

• Mov bx, Wordlist +2

• Mov edx, LongVal

Direct Offset Operands

• .data

• Array db 0ah, 0bh, 0ch, 0dh

• .code

• Mov al, array ; 0ah-al

• Mov bl, array +1 ; 0bh bl

• Mov cl, array + 2 ; 0ch cl

• Mov dl, array +3 ; 0dh dl

Another Example

IA – 32 Processor Architecture

• IA – 32 processor have three basic mode of operations:

• 1. Protected Mode

• 2. Real-address Mode

• 3. System Management Mode

Protected Mode

• IA-32 processors have three basic modes of operation: Protected mode, Real-address mode and System Management mode. In addition, the Virtual-8086 mode is a special case of Protected mode.

1. Protected Mode

• Protected mode is the native state of the processor, in which all instructions and features are available.

• Programs are given separate memory areas (called segment), and the processor detects any attempt by a program to reference memory outside its assigned segment.

• Each program can address up to 4GB memory.

Virtual – 8086 Mode

• While in Protected mode, the processor can directly execute Real-address mode software such as MS-DOS programs in a safe multitasking environment.

• In other word, even is an MS-DOS program crashes, it will not affect other program running at the same time.

Real-address mode

• It offers us a few more features, such as the ability to switch into other two modes.

• Only 1 MB of memory can be addressed:

• 00000h-FFFFFh

• The processor can only run one program a time.

System Management Mode

• SSM-mode• It provides an operating system with a mechanism

for implementing such functions as power management and system security.

• These functions are usually implemented by computer manufacturers who want to customize the processor for a particular system setup.

Homework11

• Write and run an assembly program under debug that will:

• 1) Add numbers from 1 to 1000.• Note: you would need these following

instructions:• A) jz – jump if zero• B) mov cx, number of times (1000 in Hex.)• C) create the labels that tells where to go.