Assembly Language Chap # 03

8/7/2019 Assembly Language Chap # 03

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Computer Organization &Computer Organization &

Assembly LanguageAssembly Language

Assembly Language Fundamentals

Adapted from the slides prepared by Kip Irvine for the book,Assembly Language for Intel-Based Computers, 5th Ed.


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Chapter OverviewChapter Overview

Basic Elements of Assembly LanguageBasic Elements of Assembly Language

Example: Adding and Subtracting IntegersExample: Adding and Subtracting Integers

Assembling, Linking, and Running ProgramsAssembling, Linking, and Running Programs

Defining DataDefining Data

Symbolic ConstantsSymbolic Constants

RealReal--Address Mode ProgrammingAddress Mode Programming


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Basic Elements of AssemblyBasic Elements of Assembly

LanguageLanguage

Integer constantsInteger constants

Integer expressionsInteger expressions

Character and string constantsCharacter and string constants

Reserved words and identifiersReserved words and identifiers Directives and instructionsDirectives and instructions

LabelsLabels

Mnemonics and OperandsMnemonics and Operands

CommentsComments ExamplesExamples


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Integer ExpressionsInteger Expressions

Operators and precedence levels:Operators and precedence levels:

Examples:Examples:


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Real Number ConstantsReal Number Constants

[{+|[{+|--}]}] integerinteger. [. [integerinteger] [] [exponentexponent]]

Exponent:E[{+|Exponent:E[{+|--}]}]integerinteger

Examples: 2., +3.0,Examples: 2., +3.0, --44.2E+0544.2E+05

Encoded RealsEncoded Reals

IEEE floatingIEEE floating--point format (e.g. +1.0point format (e.g. +1.0Decimal = 3F800000r)Decimal = 3F800000r)


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Character and String ConstantsCharacter and String Constants

Enclose character in single or double quotesEnclose character in single or double quotes

'A', "x"'A', "x"

ASCII character = 1 byteASCII character = 1 byte

Enclose strings in single or double quotesEnclose strings in single or double quotes "ABC""ABC"

'xyz''xyz'

Each character occupies a single byteEach character occupies a single byte

Embedded quotes:Embedded quotes:

This isnt a test"This isnt a test"

'Say "Goodnight," Gracie''Say "Goodnight," Gracie'


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Reserved Words and IdentifiersReserved Words and Identifiers Reserved words cannot be used as identifiersReserved words cannot be used as identifiers

Instruction mnemonics (MOV), directives (.code), typeInstruction mnemonics (MOV), directives (.code), typeattributes (BYTE, WORD), operators (=), predefinedattributes (BYTE, WORD), operators (=), predefinedsymbols (@data)symbols (@data)

See MASM reference in Appendix ASee MASM reference in Appendix A IdentifiersIdentifiers

11--247 characters, including digits247 characters, including digits

notnot case sensitivecase sensitive

first character must be a letter, _, @, ?, or $first character must be a letter, _, @, ?, or $Examples: var1, Count, $first, _main, @@myfileExamples: var1, Count, $first, _main, @@myfile


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DirectivesDirectives

Commands that are recognized and acted uponCommands that are recognized and acted uponby the assemblerby the assembler

Not part of the Intel instruction setNot part of the Intel instruction set

Used to declare code, data areas, selectUsed to declare code, data areas, selectmemory model, declare procedures, etc.memory model, declare procedures, etc.

not case sensitivenot case sensitive

Different assemblers have different directivesDifferent assemblers have different directives

NASM not the same as MASM, for exampleNASM not the same as MASM, for exampleExamples:Examples:.data, .code.data, .code


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InstructionsInstructions Assembled into machine code byAssembled into machine code by

assemblerassembler

Executed at runtime by the CPUExecuted at runtime by the CPU

We use the Intel IAWe use the Intel IA--32 instruction set32 instruction set

An instruction contains:An instruction contains:

LabelLabel (optional)(optional)

MnemonicMnemonic (required)(required) OperandOperand (depends on the instruction)(depends on the instruction)

CommentComment (optional)(optional)Label: Mnemonic Operand(s) ;Comment


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LabelsLabels Act as place markersAct as place markers

marks the address (offset) of code and datamarks the address (offset) of code and data

Follow identifier rulesFollow identifier rules

Data labelData label must be uniquemust be unique

example:example: count DWORD 100count DWORD 100 (not followed by colon)(not followed by colon)

Code labelCode label target of jump and loop instructionstarget of jump and loop instructions

example:example: target:target: (followed by colon)(followed by colon)

..

jmp targetjmp target


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Mnemonics and OperandsMnemonics and OperandsInstruction MnemonicsInstruction Mnemonics

memory aidmemory aid

examples: MOV, ADD, SUB, MUL, INC,examples: MOV, ADD, SUB, MUL, INC,

DECDECOperandsOperands

constant (immediate value),constant (immediate value), 9696

constant expression,constant expression,2+42+4

Register,Register, eaxeax

memory (data label),memory (data label), countcount

Constants and constant ex ressions are oftenConstants and constant ex ressions are often


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CommentsComments Comments are good!Comments are good!

explain the program's purposeexplain the program's purpose

when it was written, and by whomwhen it was written, and by whom

revision informationrevision information

tricky coding techniquestricky coding techniques

applicationapplication--specific explanationsspecific explanations

SingleSingle--line commentsline comments

begin with semicolon (;)begin with semicolon (;)

MultiMulti--line commentsline comments

begin with COMMENT directive and a programmerbegin with COMMENT directive and a programmer--chosenchosencharactercharacter

end with the same programmerend with the same programmer--chosen characterchosen character

COMMENT !

This is a comment

and this line is also a comment!


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Instruction Format ExamplesInstruction Format Examples No operandsNo operands

stcstc ; set Carry flag; set Carry flag

One operandOne operand

inc eaxinc eax ; register ; register

inc myByteinc myByte ; memory; memory

Two operandsTwo operands

add ebx, ecxadd ebx, ecx ; register, register; register, register

sub myByte, 25sub myByte, 25 ; memory, constant; memory, constant

add eax, 36 * 25add eax, 36 * 25 ; register, constant; register, constant--

expressionexpression


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What's NextWhat's Next Basic Elements of Assembly LanguageBasic Elements of Assembly Language Example: Adding and SubtractingExample: Adding and Subtracting

IntegersIntegers Assembling, Linking, and Running ProgramsAssembling, Linking, and Running Programs Defining DataDefining Data Symbolic ConstantsSymbolic Constants RealReal--Address Mode ProgrammingAddress Mode Programming


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xamp e: ng an u tract ngxamp e: ng an u tract ng

IntegersIntegers

TITLE Add and Subtract (AddSub.asm)

; This program adds and subtracts 32-bit integers.

INCLUDEIrvine32.inc

.codemain PROC

mov eax,10000h ; EAX = 10000h

add eax,40000h ; EAX = 50000h

sub eax,20000h ; EAX = 30000h

call DumpRegs ; d isplay registers

exitmain ENDP

END main


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Example OutputExample OutputProgram output, showing registers and flags:

EAX=00030000 EBX=7FFDF000 ECX=00000101 EDX=FFFFFFFF

ESI=00000000 EDI=00000000 EBP=0012FFF0 ESP=0012FFC4

EIP=00401024 EFL=00000206 CF=0 SF=0 ZF=0 OF=0


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Suggested Coding StandardsSuggested Coding Standards Some approaches to capitalizationSome approaches to capitalization

capitalize nothingcapitalize nothing

capitalize everythingcapitalize everything

capitalize all reserved words, includingcapitalize all reserved words, includinginstruction mnemonics and registerinstruction mnemonics and registernamesnames

capitalize only directives and operatorscapitalize only directives and operators

Other suggestionsOther suggestions

descriptive identifier namesdescriptive identifier names

spaces surrounding arithmetic operatorsspaces surrounding arithmetic operators

blank lines between proceduresblank lines between procedures


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Suggested Coding StandardsSuggested Coding Standards(cont.)(cont.)

Indentation and spacingIndentation and spacing code and data labelscode and data labels no indentationno indentation

executable instructionsexecutable instructions indent 4indent 4--55

spacesspaces comments: begin at column 40comments: begin at column 40--45,45,

aligned verticallyaligned vertically

11--3 spaces between instruction and its3 spaces between instruction and its

operandsoperands ex: mov ax,bxex: mov ax,bx

11--2 blank lines between procedures2 blank lines between procedures


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Program TemplateProgram TemplateTITLE ProgramTemplate (Template.asm)

; ProgramDescription:

; Author:

; Creation Date:

; Revisions:

; Date: Modified by:

INCLUDEIrvine32.inc

.data

; (insert variables here)

.code

main PROC

; (insert executable instructions here)

exitmain ENDP

; (insert additional procedures here)

END main


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What's NextWhat's Next Basic Elements of Assembly LanguageBasic Elements of Assembly Language

Example: Adding and SubtractingExample: Adding and SubtractingIntegersIntegers

Assembling, Linking, and RunningAssembling, Linking, and Running

ProgramsPrograms





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, ,, ,

ProgramsPrograms

AssembleAssemble--LinkLink--Execute CycleExecute Cycle

make32.batmake32.bat

Listing FileListing File

Map FileMap File


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make32.batmake32.bat

Called aCalled a batch filebatch file

Run it to assemble and link programsRun it to assemble and link programs

Contains a command that executesContains a command that executesML.EXE (the Microsoft Assembler)ML.EXE (the Microsoft Assembler)

Contains a command that executesContains a command that executesLINK32.EXE (the 32LINK32.EXE (the 32--bit Microsoft Linker)bit Microsoft Linker)

CommandCommand--Line syntax:Line syntax:make32make32 progNameprogName

(progName(progName includes the .asm extension)includes the .asm extension)(use make16.bat to assemble and link Real-mode programs)


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Listing FileListing File Use it to see how your program isUse it to see how your program is

compiledcompiled

ContainsContains

source codesource code

addressesaddresses

object code (machine language)object code (machine language)

segment namessegment names symbols (variables, procedures, andsymbols (variables, procedures, and

constants)constants)

Example:Example: addSub.lstaddSub.lst


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Map FileMap File Information about each programInformation about each program

segment:segment:

starting addressstarting address

ending addressending address sizesize

segment typesegment type

Example:Example: addSub.mapaddSub.map (16(16--bit version)bit version)


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Assembling, Linking, and RunningAssembling, Linking, and RunningProgramsPrograms


Symbolic ConstantsSymbolic Constants RealReal--Address Mode ProgrammingAddress Mode Programming


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Defining DataDefining Data Intrinsic Data TypesIntrinsic Data Types Data Definition StatementData Definition Statement

Defining BYTE and SBYTE DataDefining BYTE and SBYTE Data

Defining WORD and SWORDDefining WORD and SWORDDataData

Defining DWORD and SDWORDDefining DWORD and SDWORDDataData

Defining QWORD DataDefining QWORD Data

Defining TBYTE DataDefining TBYTE Data

Defining Real Number DataDefining Real Number Data

Little Endian OrderLittle Endian Order


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Intrinsic Data TypesIntrinsic Data Types (1 of 2)(1 of 2) BYTE, SBYTEBYTE, SBYTE

88--bit unsigned integer; 8bit unsigned integer; 8--bit signedbit signedintegerinteger

WORD, SWORDWORD, SWORD 1616--bit unsigned & signed integerbit unsigned & signed integer

DWORD, SDWORDDWORD, SDWORD

3232--bit unsigned & signed integerbit unsigned & signed integer QWORDQWORD

6464--bit integerbit integer

TBYTETBYTE


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Intrinsic Data TypesIntrinsic Data Types (2 of 2)(2 of 2) REAL4REAL4

44--byte IEEE short realbyte IEEE short real

REAL8REAL8

88--byte IEEE long realbyte IEEE long real

REAL10REAL10

1010--byte IEEE extended realbyte IEEE extended real


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Data Definition StatementData Definition Statement A data definition statement sets aside storageA data definition statement sets aside storage

in memory for a variable.in memory for a variable.

May optionally assign a name (label) to theMay optionally assign a name (label) to thedatadata

Syntax:Syntax:[[namename]]directivedirective initializerinitializer [,[,initializerinitializer] . . .] . . .

value1 BYTE 10value1 BYTE 10

All initializers become binary data in memoryAll initializers become binary data in memory


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Defining BYTE and SBYTE DataDefining BYTE and SBYTE Data

value1 BYTE 'A' ; character constant

value2 BYTE 0 ; smallest unsigned byte

value3 BYTE 255 ; largest unsigned byte

value4 SBYTE -128 ; smallest signed byte

value5 SBYTE +127 ; largest signed byte

value6 BYTE ? ; uninitialized byte

Each of the following defines a single byte of storage:

A variable name is a data label that implies an offset (an address). If you declare a SBYTE variable, the Microsoft debugger will

automatically display its value in decimal with a leading sign.


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Defining Byte ArraysDefining Byte Arrays

list1 BYTE 10,20,30,40

list2 BYTE 10,20,30,40

BYTE 50,60,70,80

BYTE 81,82,83,84

list3 BYTE ?,32,41h,00100010b

list4 BYTE 0Ah,20h,A,22h

Examples that use multiple initializers:


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Defining StringsDefining Strings (1 of 3)(1 of 3)

A string is implemented as an array ofA string is implemented as an array ofcharacterscharacters For convenience, it is usually enclosed inFor convenience, it is usually enclosed in

quotation marksquotation marks

It often will beIt often will be nullnull--terminatedterminated

Examples:Examples:

str1 BYTE "Enter your name",0

str2 BYTE 'Error: halting program',0

str3 BYTE 'A','E','I','O','U'

greeting BYTE "Welcome to the Encryption Demo program "

BYTE "created by Kip Irvine.",0greeting2 \

BYTE "Welcome to the Encryption Demo program "

BYTE "created by Kip Irvine.",0


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Defining StringsDefining Strings (cont.)(cont.) To continue a single string across multipleTo continue a single string across multiple

lines, end each line with a comma:lines, end each line with a comma:

menu BYTE "Checking Account",0dh,0ah,0dh,0ah,

"1. Create a new account",0dh,0ah,"2. Open an existing account",0dh,0ah,

"3. Credit the account",0dh,0ah,

"4. Debit the account",0dh,0ah,

"5. Exit",0ah,0ah,

"Choice> ",0


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Defining StringsDefining Strings (cont.)(cont.) EndEnd--ofof--line character sequence:line character sequence:

0Dh = carriage return0Dh = carriage return

0Ah = line feed0Ah = line feed

str1 BYTE "Enter your name: ",0Dh,0AhBYTE "Enter your address: ",0

newLine BYTE 0Dh,0Ah,0

Idea: Define all strings used by your program in the samearea of the data segment.


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Using the DUP OperatorUsing the DUP Operator

Use DUP to allocate (create space for) an arrayUse DUP to allocate (create space for) an arrayor string. Syntax:or string. Syntax: countercounterDUP (DUP ( argumentargument ))

CounterCounterandand argumentargumentmust be constants ormust be constants or

constant expressionsconstant expressionsvar1 BYTE 20 DUP(0) ; 20 bytes, all equal to zerovar2 BYTE 20 DUP(?) ; 20 bytes, uninitialized

var3 BYTE 4 DUP("STACK") ; 20 bytes: "STACKSTACKSTACKSTACK"

var4 BYTE 10,3 DUP(0),20 ; 5 bytes


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Defining WORD and SWORDDefining WORD and SWORD

DataData Define storage for 16Define storage for 16--bit integersbit integers

or double charactersor double characters

single value or multiple valuessingle value or multiple values

word1 WORD 65535 ; largest unsigned valueword2 SWORD 32768 ; smallest signed value

word3 WORD ? ; uninitialized, unsigned

word4 WORD "AB" ; double characters

myList WORD 1,2,3,4,5 ; array of words

array WORD 5 DUP(?) ; uninitialized array


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Defining DWORD andDefining DWORD and

SDWORDDataSDWORDData

val1 DWORD 12345678h ; unsigned

val2 SDWORD 2147483648 ; signed

val3 DWORD 20 DUP(?) ; unsigned array

val4 SDWORD 3,2,1,0,1 ; signed array

Storage definitions for signed and unsigned 32-bitintegers:


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Defining QWORD, TBYTE, RealDefining QWORD, TBYTE, Real

DataData

quad1 QWORD 1234567812345678h

val1 TBYTE 1000000000123456789AhrVal1 REAL4 -2.1

rVal2 REAL8 3.2E-260

rVal3 REAL10 4.6E+4096

ShortArray REAL4 20 DUP(0.0)

Storage definitions for quadwords, tenbyte values,and real numbers:


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Little Endian OrderLittle Endian Order All data types larger than a byte store theirAll data types larger than a byte store their

individual bytes in reverse order.individual bytes in reverse order.

The least significant byte occurs at theThe least significant byte occurs at the

first (lowest) memory address.first (lowest) memory address.

Example:Example:

val1 DWORD 12345678hval1 DWORD 12345678h


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Adding Variables to AddSubAdding Variables to AddSubTITLE Add and Subtract, Version 2 (AddSub2.asm)

; This program adds and subtracts 32-bit unsigned

; integers and stores the sumin a variable.

INCLUDEIrvine32.inc

.data

val1 DWORD 10000h

val2DWOR

D40000

hval3 DWORD 20000h

finalVal DWORD ?

.code

main PROC

mov eax,val1 ; start with 10000h

add eax,val2 ; add 40000h

sub eax,val3 ; subtract 20000hmov finalVal,eax ; store the result (30000h)

call DumpRegs ; d isplay the registers

exit

main ENDP

END main


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Declaring Uninitialized DataDeclaring Uninitialized Data Use the .data? directive to declare anUse the .data? directive to declare an

unintialized data segment:unintialized data segment:

.data?.data?

Within the segment, declare variables with "?"Within the segment, declare variables with "?"initializers:initializers:

smallArray DWORD 10 DUP(?)smallArray DWORD 10 DUP(?)

.data.data

smallArray DWORD 10 DUP(0)smallArray DWORD 10 DUP(0)

.data?.data?

bigArray DWORD 5000 DUP(?)bigArray DWORD 5000 DUP(?)

Advantage: the program's EXE file size is reduced.


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Mixing code and dataMixing code and data

.code.code

mov eax, ebxmov eax, ebx

.data.data

temp DWORD ?temp DWORD ?.code.code

mov temp, eaxmov temp, eax


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Symbolic ConstantsSymbolic Constants EqualEqual--Sign DirectiveSign Directive

Calculating the Sizes of Arrays andCalculating the Sizes of Arrays andStringsStrings

EQU DirectiveEQU Directive

TEXTEQU DirectiveTEXTEQU Directive


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EqualEqual--Sign DirectiveSign Directive namename == expressionexpression

expression is a 32expression is a 32--bit integer (expression orbit integer (expression orconstant)constant)

may be redefinedmay be redefined namename is called ais called a symbolic constantsymbolic constant

good programming style to use symbolsgood programming style to use symbols

Easier to modifyEasier to modify

Easier to understand,Easier to understand, ESC_keyESC_key

Array DWORDCOUNTDUP(0)Array DWORDCOUNTDUP(0)

COUNT=5COUNT=5

Mov al, COUNTMov al, COUNT

COUNT = 500

.

.

mov al,COUNT


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Calculating the Size of a ByteCalculating the Size of a Byte

ArrayArray Current location counter: $Current location counter: $

subtract address of listsubtract address of list

difference is the number of bytesdifference is the number of bytes

list BYTE 10,20,30,40

BYTE 100 DUP(0)

ListSize = ($ - list)


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Calculating the Size of a WordCalculating the Size of a Word

ArrayArrayDivide total number of bytes by 2 (the size of aDivide total number of bytes by 2 (the size of a

word)word)

list WORD 1000h,2000h,3000h,4000h

ListSize = ($ - list) / 2

a cu a ng e ze o aa cu a ng e ze o a


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a cu a ng e ze o aa cu a ng e ze o a

Doubleword ArrayDoubleword Array

Divide total number of bytes by 4Divide total number of bytes by 4

(the size of a doubleword)(the size of a doubleword)

list DWORD 1,2,3,4ListSize = ($ - list) / 4


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EQU directiveEQU directive name EQU expressionname EQU expression

name EQU symbolname EQU symbol

name EQU name EQU

Define a symbol as either an integer or textDefine a symbol as either an integer or textexpression.expression.

Can be useful for nonCan be useful for non--integer constantinteger constant

Cannot be redefinedCannot be redefined


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EQU directiveEQU directivePIEQU

pressKey EQU

.data

prompt BYTE pressKey

Matrix1 EQU 10*10

matrix1 EQU

.data

M1 WORD matrix1 ; M1 WORD 100

M2 WORD matrix2 ; M2 WORD 10*10


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TEXTEQUDirectiveTEXTEQUDirective Define a symbol as either an integer or textDefine a symbol as either an integer or text

expression.expression.

Called aCalled a text macrotext macro

Can be redefinedCan be redefinedcontinueMsg TEXTEQU

rowSize = 5

.data

prompt1 BYTE continueMsg

count TEXTEQU %(rowSize * 2) ; evaluates the expression

setupALTEXTEQU

.code

setupAL ; generates: "mov al,10"


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Symbolic ConstantsSymbolic Constants RealReal--Address Mode ProgrammingAddress Mode Programming

R lR l Add M dAdd M d


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RealReal--Address ModeAddress Mode

ProgrammingProgramming Generate 16Generate 16--bit MSbit MS--DOS ProgramsDOS Programs AdvantagesAdvantages

enables calling of MSenables calling of MS--DOS and BIOSDOS and BIOS

functionsfunctions no memory access restrictionsno memory access restrictions

DisadvantagesDisadvantages

must be aware of both segments andmust be aware of both segments andoffsetsoffsets

cannot call Win32 functions (Windows 95cannot call Win32 functions (Windows 95onward)onward)

limited to 640K program memorylimited to 640K program memory


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Add and Subtract, 16Add and Subtract, 16--Bit VersionBit VersionTITLE Add and Subtract, Version 2 (AddSub2r.asm)INCLUDEIrvine16.inc

.data

val1 DWORD 10000h

val2 DWORD 40000h

val3 DWORD 20000h

finalVal DWORD ?

.code

main PROC

mov ax,@data ; initialize DS

mov ds,ax

mov eax,val1 ; get first value

add eax,val2 ; add second value

sub eax,val3 ; subtract third value

mov finalVal,eax ; store the result

call DumpRegs ; d isplay registers

exit

main ENDP

END main


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SummarySummary

Integer expression, character constantInteger expression, character constant

directivedirective interpreted by the assemblerinterpreted by the assembler

instructioninstruction executes at runtimeexecutes at runtime

code, data, and stack segmentscode, data, and stack segments

source, listing, object, map, executablesource, listing, object, map, executablefilesfiles

Data definition directives:Data definition directives: BYTE, SBYTE, WORD, SWORD, DWORD,BYTE, SBYTE, WORD, SWORD, DWORD,

SDWORD, QWORD, TBYTE, REAL4, REAL8,SDWORD, QWORD, TBYTE, REAL4, REAL8,and REAL10and REAL10

$$

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Assembly Language Chap # 03

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