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© 2006 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.Brey: The Intel Microprocessors, 7e

Chapter 3Chapter 3

Addressing Modes Addressing Modes

Barry B. BreyBarry B. [email protected]@ee.net

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Addressing Modes Addressing Modes

In order to write a program addressing modesIn order to write a program addressing modes

must be thoroughly understood.must be thoroughly understood.

There are many addressing modes, but the mostThere are many addressing modes, but the most

common are easy to master and represent mostcommon are easy to master and represent most

instructions in most programs.instructions in most programs.

Register addressing, immediate addressing,Register addressing, immediate addressing,

direct addressing, and simple forms of indirectdirect addressing, and simple forms of indirectaddressing are the most common addressingaddressing are the most common addressing

modes.modes.

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Stack addressing is also used with theStack addressing is also used with the

PUSH and POP instructions and as a wayPUSH and POP instructions and as a wayto link a program to its procedures or to link a program to its procedures or

functions.functions.

Program flow instructions are either Program flow instructions are either

unconditional or conditional.unconditional or conditional.

Conditional program flow instructions areConditional program flow instructions are

the ³if´ statements of assembly language.the ³if´ statements of assembly language.

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Data Addressing ModesData Addressing Modes

Data addressing modes are presents withData addressing modes are presents with

the MOV instruction because it is by far the MOV instruction because it is by far

the most common instruction in a program.the most common instruction in a program. MOV really moves nothing. MOV copiesMOV really moves nothing. MOV copies

the source into the destination. It probablythe source into the destination. It probably

should be named COP for copy, but it isshould be named COP for copy, but it is

not.not.

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Register Register

MOV EAX,EBXMOV EAX,EBX

MOV CX,DXMOV CX,DX

MOV AH,ALMOV AH,AL MOV AX,DSMOV AX,DS

MOV ES,CXMOV ES,CX

ADD AL,CL (most instructions use it) ADD AL,CL (most instructions use it) OR AX,DXOR AX,DX

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ImmediateImmediate

MOV EAX,234HMOV EAX,234H

MOV CX,2MOV CX,2

MOV AL,34HMOV AL,34H ADD AL,3 ADD AL,3

SUB CL,4SUB CL,4

AND EAX,1 AND EAX,1

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DirectDirect

MOV BOB,EAXMOV BOB,EAX

MOV FRED,CXMOV FRED,CX

MOV BILLY,ALMOV BILLY,AL MOV EDI,RALPHMOV EDI,RALPH

MOV AX,STEVEMOV AX,STEVE

MOV DS,BARNEYMOV DS,BARNEY MOV AL,DS:[1000H]MOV AL,DS:[1000H]

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Register IndirectRegister Indirect

MOV AL,[BX]MOV AL,[BX]

MOV AX[EBX]MOV AX[EBX]

MOV [EDI],EAXMOV [EDI],EAX MOV [EAX],EDXMOV [EAX],EDX

MOV BYTE PTR [EAX],6MOV BYTE PTR [EAX],6

MOV WORD PTR [ECX],12MOV WORD PTR [ECX],12 MOV DWORD PTR [ESI],2345HMOV DWORD PTR [ESI],2345H

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Base Plus IndexBase Plus Index

MOV AL,[BX+SI]MOV AL,[BX+SI]

MOV [BX+DI],AXMOV [BX+DI],AX

MOV [BP+SI],EAXMOV [BP+SI],EAX MOV AL,[BP+DI]MOV AL,[BP+DI]

MOV WORD PTR [BX+SI],5MOV WORD PTR [BX+SI],5

ADD AL,[BX+DI] ADD AL,[BX+DI]

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Register RelativeRegister Relative

MOV AL,[BX+3]MOV AL,[BX+3]

MOV AX,[DI+20H]MOV AX,[DI+20H]

MOV [EDI+200H],EAXMOV [EDI+200H],EAX MOV [BXMOV [BX--33],ECX33],ECX

ADD BYTE PTR [BX+2],5 ADD BYTE PTR [BX+2],5

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Relative Plus IndexRelative Plus Index

MOV AL,[BX+SI+22]MOV AL,[BX+SI+22]

MOV [BX+DIMOV [BX+DI--22],AX22],AX

MOV EAX,[EBX+EDI+100H]MOV EAX,[EBX+EDI+100H]

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Scaled IndexScaled Index

MOV EAX,[EBX+ 4*ECX]MOV EAX,[EBX+ 4*ECX]

MOV AX,[EDI+2*EBX]MOV AX,[EDI+2*EBX]

MOV [EAX+2*EBX],DXMOV [EAX+2*EBX],DX MOV [4*ECX],EBXMOV [4*ECX],EBX

ADD AL,[ECX+EBX] ADD AL,[ECX+EBX]

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Program FlowProgram Flow

Program flow instruction are unconditionalProgram flow instruction are unconditional

(JMP) or conditional (JNZ).(JMP) or conditional (JNZ).

Flow instructions are short (Flow instructions are short (+127,+127, --128),128),near (near (±±32K), or far (anywhere in the32K), or far (anywhere in the

memory).memory).

Conditionals do not contain the far type.Conditionals do not contain the far type.

Labels are followed by a colon if they areLabels are followed by a colon if they are

jumped to in a program. jumped to in a program.

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PUSH AXPUSH AX

PUSH EAXPUSH EAX POP AXPOP AX

POP EAXPOP EAX

PUSH BOBPUSH BOB POP BOBPOP BOB

PUSHFPUSHF

POPFPOPF

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