4615-4713_chapter 2.ppt

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The x86 Microprocessor - Lyla B Das 1

PROGRAMMING

CONCEPTS 1

CHAPTER 2

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ASSEMBLY LANGUAGE

PROGRAMMINGTo code efciently in assembly langage !o" a

#a"ticla" #"ocesso"$ t%e #"e"e&isites a"e

a good 'no(ledge o! t%e inte"nal a"c%itect"eo! t%e #"ocesso" and add"essing modes

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T%e Assembly P"ocessAn assemble" is a t"anslato" t%at t"anslates

so"ce inst"ctions )in symbolic langage*

into ta"get inst"ctions )in mac%ine langage*on a one+to+one basis

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,eat"es o! assemble"s-abels a"e sed !o" memo"y add"esses

-abels a"e sed !o" constants

Mac"os a"e allo(ed

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Inst"ctions and .i"ecti/esInst"ctions a"e e0ectable statements

.i"ecti/es a"e non+e0ectable

.i"ecti/es a"e also called #sedo inst"ctions.i"ecti/es aid t%e assembly #"ocess

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%at t%e assemble" doesIt ta'es t%e so"ce code )in assembly

langage* and

con/e"ts it to t%e ob3ect code in mac%inelangage

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ASSEM4-ERS ,OR 056NASM$ ,ASM$ MASM$ TASM and H-A

,ASM and NASM can "n nde" .OS$ -in0

and indo(sTASM and MASM a"e /e"y #o#la"

It is found now that Windows 7, a new64-bit operating system, does not

directly support 16-bit programs so 16bit assemblers may not work withWindows 7 directly

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DOS.OS stands !o" .is' O#e"ating Systems It

cold be an ac"onym !o" any OS$ bt it is mosto!ten sed as a s%o"t%and !o" MS+.OS)Mic"oso!t .is' O#e"ating Systems*

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BIOS and DOS function calls

A set o! !nctions !o" sing I7O de/ices

Can be sed !o" dis#laying data

Can be sed !o" in#tting data !"om t%e'eyboa"d

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T%e E8IT command is a s%o"t%and notation!o"

MO9 AH $:CHINT 21H

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.OS ,nction Calli* Read t%e 'eyboa"d (it% ec%o

MO9 AH$ ;1 INT 21H

T%is call e0its (it% t%e ASCII /ale o! t%e 'ey#"essed$ being a/ailable in A-

T%e 'ey #"essed is also echoed on t%e sc"een

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.OS ,nction Call < Contdii* Read =eyboa"d (it%ot ec%o

MO9 AH$ ;5

INT 21HT%is call e0its (it% t%e ASCII /ale o! t%e 'ey

#"essed being a/ailable in A-

T%e 'ey #"essed is not echoed on t%e

sc"een

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.is#laying a c%a"acte"iii* "ite a c%a"acte" to t%e standa"d dis#lay

nit

,o" t%is $t%e ASCII /ale o! t%e c%a"acte" to bedis#layed s%old be in .-

MO9 .-$ >S?

MO9 AH$ ;2

INT 21H

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STRING .ISP-A@i/* .is#lay a c%a"acte" st"ing on t%e standa"d

dis#lay nit

T%e logical add"ess .S.8 s%old #oint to t%ebeginning o! t%e st"ing

T%is is to be !ollo(ed by t%e !ollo(inginst"ctions

MO9 AH$ ;B

INT 21H

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%y MASM Mic"oso!t %as ("itten conside"able

docmentation

T%i"d #a"ties %a/e ("itten assembly langage"e!e"ence manals !o" MASM

T%e /e"sions o! MASM 6; and abo/e %a/e alot mo"e !eat"es )aimed at sim#liDcation o!

("iting code* t%an #"e/ios /e"sions

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He"e (e se MASM 61:$ (%ic% is .OS basedIn t%is$ .OS and 4IOS inte""#ts can be sed

MASMF2$ (%ic% is (indo(s basedIn t%is$ .OS and 4IOS inte""#ts cannot be

sed

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ASSEM4-@ -ANGAGE

PROGRAMMINGSTEPS

"ite t%e code (it% t%e %el# o! an edito"

O#en t%e .OS (indo(

Go to t%e MASM and t%en to t%e 4IN di"ecto"yAssemble t%e code

-in' t%e code

Rn t%e e0ectable Dle

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Memo"y Models,o" deDning segments

.ot models %a/e s%o"t cts

T%e tiny model is sed (%en only onesegment is needed

To s#eci!y a segment$ ("ite

. MO.E- MO.E- NAME

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E0am#le 21 < T%e Tiny Model MO.E- TIN@

CO.E

STARTPMO9 A-$6H

MO9 4-$:H

A.. A-$4-

MO9 .-$A-E8IT

EN.

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Sa/e it as tinyasm

O#en MASM and go to t%e 4IN di"ecto"yse t%e !ollo(ing commands

l tin!.as "fo# asse$lin% and lin&in% l'(l tin!.as J!o" t%e list Dle

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T%e "eslt o! assembling and

lin'ing)*+as,.-+BIN/l tin!.asMic"oso!t )R* Mac"o Assemble" 9e"sion 61:5:::Co#y"ig%t )C* Mic"oso!t Co"# 1B51+1BB All "ig%ts "ese"/edAssembling tinymasmMic"oso!t )R* Segmented E0ectable -in'e" 9e"sion 6;FFB

.ec 1BB:Co#y"ig%t )C* Mic"oso!t Co"# 1B5:+1BBF All "ig%ts "ese"/edOb3ect Modles Kob3L tinymob3 7tRn ,ile KtinymcomL tinymcom

-ist ,ile Knlma#L N--ib"a"ies KlibL.eDnitions ,ile Knlde!L

21

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E0am#le 2FPa"t o! t%e -ist Dle

MO.E- TIN@

;;;; CO.E

;1;; 4; 6 MO9 A-$6H;1;2 4F : MO9 4-$:H

;1;: ;2 CF A.. A-$4-

;1;6 5A .; MO9 .-$A-

E8IT

EN.

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S%o"t cts in t%e modelE8IT

STARTP

T%e (o"'ing o! all t%ese can be obtained bysing t%e listall di"ecti/e in t%e #"og"am

E8IT gets t"anslated to

MO9 AH$:CH

INT 21H

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sing t%e debgge"To ente" t%e debgge"$ ty#e de$u%

tin!.co

e get an nde"sco"e as t%e #"om#tOn ty#ing >"?$ (e can see t%e contents o! t%e

"egiste"s$ be!o"e e0ection o! t%e #"og"am

No( ty#e >?$ (%ic% is t%e command !o"

nassembling

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E0am#le 2C:\masm6.14\BIN>debug tinym.com

-r

AX=0000 BX=0000 CX=010C DX=0000 SP=0000 BP=0000SI=0000 DI=0000

DS=13AD ES=13AD SS=13BD CS=13BD IP=0100 NV UP EI PLNZ NA PO NC

13BD:0100 B067 MOV AL,67

-u

13BD:0100 B067 MOV AL,67

13BD:0102 B345 MOV BL,45

13BD:0104 02C3 ADD AL,BL

13BD:0106 8AD0 MOV DL,AL

13BD:0108 B44C MOV AH,4C

13BD:010A CD21 INT 21

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)OM and E0E 1lesA tiny model gene"ates only a com Dle$

(%ile any ot%e" memo"y model gene"ates an

e0e Dle

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,eat"es o! a com Dle Sie is limited to 6:=

Only one segment$ (%ic% is t%e code

segment .ata is deDned in t%is code segment

Code sta"ts at oset ;1;; H$

Smalle" Dle com#a"ed to e0e Dles

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E0am#le 2

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.ata deDnitions in MASM Table

21

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T%e small modelHe"e t(o segments a"e sed ?*

4-AN= .4 1;.P)*

R.S . : .P),,;,H*

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2he E6U Di#ecti3esed to e&ate names to constants

T%e assemble" 3st "e#laces t%e names by t%e/ales mentioned

E0am#les

TEMP EQ F:

PRICE EQ 1BB

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E0am#le 21;

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2he ORG Di#ecti3eORG is a di"ecti/e (%ic% means >o"igin?

In t%e conte0t o! assembly langage

#"og"amming$ it can c%ange t%e location o!sto"age o! data o" code in memo"y

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E0am#le 211a

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E0am#le211b

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2a$le 7.7 Othe# Models

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E0am#le 212 ,ll segment model

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Gene"al "les !o" ("iting assembly

langage1 All labels s%old begin (it% a lette" o" t%e

s#ecial c%a"acte"s $ $ and

2 A label can %a/e 1 to F1 c%a"acte"s (%ic%may be digits $lette"s in ##e" o" lo(e" caseo" t%e s#ecial c%a"acte"s at )*$dolla")* $nde"sco"e )* $dot)* o" &estion ma"')*

F No "ese"/ed (o"ds o! MASM may be sed: Eac% label mst be ni&e

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E0am#le 21F

4615-4713_chapter 2.ppt

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