Micro 133 Prelim Lecture 4 - Microprocessor_s Addressing Modes

7/23/2019 Micro 133 Prelim Lecture 4 - Microprocessor_s Addressing Modes

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MICROPROCESSORS

ADDRESSING MODESMicro 133: Microprocessor Systems

Prelim Lecture 4

by:Engr. Ricrey E. Marquez, CpE, MSCS


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Accessing data in high-level language suchC, C++, or Pascal

C = A + B

Accessing data in DEBUG or Assembly

MOV AX,[0200] ;the A value

MOV BX, [0202] ;the B value

ADD AX, BX ; A + B

MOV [0300], AX ;store result at C

Choice of addressing mode used depends upon the type of data being

accessed.

A constant,

A variablepiece o i!or"atio! or

A! ite" #ithi! a! array of data$

INTRODUCTION TO ADDRESSING

MODESMICROPROCESSORS ADDRESSING MODES


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Intel family supportsfouraddressing modes (in general)

Modes differ in the location data and address calculations

All nodes involvesphysical addressgeneration

8086 Instruction Syntax

Lines of code

Label:Instruction ;Comment/s

InstructionOpcode [operand 1], [operand 2]Mnemonic Destination Source

8088/8086 INSTRUCTION SYNTAXMICROPROCESSORS ADDRESSING MODES


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OperandsThese are destination address and source address of

data.

Opcode(Operation code)This tells the microprocessor which operation to perform

The way in which these addresses are specified is

named the addressing mode for thesourceanddestinationaddress.

Source operandis to the right

Destination operandis to the left

8088/8086 INSTRUCTION SYNTAXMICROPROCESSORS ADDRESSING MODES


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Data Addressing Modes Register Addressing Mode (General)

Immediate Addressing Mode (Constant)

Memory Addressing Modes Direct Addressing Mode (Variable)

Register Indirect Addressing Mode (Arrays)

Base-plus-Index Addressing Mode (Complex Array)

Register Relative Addressing Mode (Complex Array)

Base-Relative-plus-Index Addressing Mode (More Complex Array)

Scaled-index Addressing Mode (More Complex Array for 32 bit)

Program Memory Addressing Modes Direct Program Memory Addressing Mode

Register Indirect Program Memory Addressing Mode

Memory Indirect Program Memory Addressing Mode

Relative Program Memory Addressing Mode (Conditional)

Stack Memory Addressing Modes

TYPES OF PS ADDRESSING



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Register Addressing Mode (General)

It uses the name of a register to identify the location of data the

data is held in the register.

Copy the content source register to a destination register

8 Working Registers AX, BX, CX, DX, SI, DI, BP, SP 16 bit wide.

Four of the registers AX, BX, CX, DXcan be thought of as single

16 bit registers or dual 8 bit registers.

Length of the registers must match

MOV AX, CX

MOV BL, CL

MOV AL, SI ;ILLEGAL

MOV AX, CH ;ILLEGAL

MOV DS, AX

MOV CS, AX ;ILLEGAL

DATA ADDRESSING MODESMICROPROCESSORS ADDRESSING MODES


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Immediate Addressing Mode (Constant)

Transfer data (constant) to into a destination register

Value moved into a register (from instruction)

Most instructions assume that the operands of an instruction are the address of the

data involved, not the data itself.

The exception to this rule is the immediate addressing mode, where the actual datanumber is specified in the instruction and is hard coded as part of the instruction

(source operand).

ITEM E!" #$%H

ITEM& E!" ########B

ITEM% E!" #D

STA'T( MOV AX, ITEMMOV BL, )*D

MOV CH, ITEM& ; ILLEGAL

MOV #CDH, BL ; ILLEGAL

MOV ITEM&, AL ; ILLEGAL

Note:EQUdirective assigns names to constant numbers and does not save memory space

DATA ADDRESSING MODESMICROPROCESSORS ADDRESSING MODES


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Labels -These are names given to an address of anopcodein code memory

Constants -These are names assigned to absolutely constant numbers, hard coded into

instructions

Variables

These are names of an address in memory However, a program reference to the variable name, as an operand, will use the contents of address

LOO+HE'E( MOV AX,BX

-M+ LOO+HE'E

CO. E!" #ABCDH

MOV AX,CO.

VA' D/ #ABCDH

MOV AX,VA'

MOV VA',BX

SOME SYMBOLS USED IN

ADDRESSING MODEMICROPROCESSORS ADDRESSING MODES


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Accessing data that is in memory is done by specifying

the address of the data.Addressis actually the offset of the data relative to the base

of the data segment.

This mode is invoked when the operand is placed in

square brackets[xxxx].

Direct Memory Addressing Mode(Variable)

Move byte or word between memory location and a register

Memory address appears in the instructions instead of data

Data accessed from a location in memory

[xxxx]is afixed addressnumber

MEMORY ADDRESSING MODESMICROPROCESSORS ADDRESSING MODES


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Examples of Direct Addressing Modes

MOV 0&%1H2, AX ;MOVE CONTENT OF AX TO

;DS:1234H; NOT ;SUPPORTED!

VA' D/ 3

VA'& DB #$$H

MOV VA',&%1H ;MOVE NUMBER 1234H TO

;VARIABLE VAR1

MOV 0VA'2,AX

MOV VA'4,&%1H

MOV /O'D +T' 0VA'42,&%1H

MOV B5TE +T' 0VA'2,&H

MOV VA'&,&%1H

MOV AH,VA'&



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Register Indirect Addressing Mode (Arrays)

Transfer data between a register and a memory location

address by a register

Sometimes need using the special assembler directiveswhen size is not clear such asBYTE PTR, WORD

PTR, DWORD PTR.

VA'DD &%167*)H

VA'&DD 8ABCDE$#H

S"M DD 3

;MOVE LOW WORD OF VAR1 TO AX

STA'T( MOV AX, /O'D +T' 0VA'2

;MOVE LOW WORD OF VAR2 TO BX

MOVBX, /O'D +T' 0VA'&2



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MOV CX, /O'D +T' 0VA'4&2

;MOVE LOW WORD OF VAR1 TO AX

MOV DX, /O'D +T' 0VA'&4&2

;ADD THE LOW WORDS

ADD AX, BX ;ADD THE HIGH WORDS

ADC CX, DX

;MOVE LOW WORD OF RESULT TO LOW WORD

;OF SUM

MOV /O'D +T' 0S"M2, AX

;MOVE HIGH WORD OF RESULT TO HIGH

;WORD OF SUM

MOV /O'D +T' 0S"M4&2, CX

'ET



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Base-plus-Index Addressing Mode

(Complex Array)

Transfer data between a register and amemory location addressed by base register

and index register

MOV 0BX4SI2,AX

MOV DX,0BX4DI2



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Register Relative Addressing

Mode (Complex Array)

Move data between a register and a

memory location addressed by specified

register plus displacement (offset)

MOV AX,0BX412

MOV BX,0S+4%2



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Base-Relative-plus-Index Addressing

Mode (More Complex Array)

Transfer data between a register and amemory location addressed by base and index

register plus displacement

MOV 0BX4SI4&2,AX

MOV DX,0BX4DI412



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Scaled-index Addressing Mode (More

Complex Array for 32 bit)

The address in the second register is modified by

scale factor

Scale factor are 1, 2, 4, or 8 for word, double word, or

quad-word access respectively.

Only available in 80386 and above microprocessor (32

bit)

MOV 0EBX4&9ECX2, AX

MOV EAX, 0EB+4)9ECX2



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The flow of a program can be controlled through

the use of differentbranching instructions

Different addressing modes are also used here to

direct the CPU to various locations of program

code

Direct Program Memory Addressing ModeJump to a location specified by a constant

-M+ #E##: ;JUMPS DIRECTLY TO CS:E1H

PROGRAM MEMORY ADDRESSING



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Register Indirect Program Memory Addressing

ModeJump to a location specified by the contents of a register

-M+ BX ;J"#$ %& %'( )**+($$ ,&-%).-(* .- BX

Memory Indirect Program Memory Addressing

ModeJump to a location given by the contents of two memory

locations pointed at by a register

-M+ 0DI2 ;REPLACES IP WITH THE CONTENTS OF THE

;MEMORY LOCATIONS POINTED

;AT BY DI AND DI / 1

PROGRAM MEMORY ADDRESSING



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Relative Program Memory Addressing Mode

(Conditional)

Jump according to some condition to a memory

location that is within128 or +127 bytesof thecurrent location

-E;-


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Stackis LIFO (LastIn,FirstOut) in the memory

Data are place byPUSHand removed byPOP

instruction

Stack memory is maintained by stack segment (SS) andstack pointer (SP) SS:SP

When a word ispushed,high 8-bitsare stored atSP-1

andlow 8-bitsare stored atSP-2, thenSPisdecremented

by 2

When a word ispoped,low 8-bitsare removed from the

locationSPandhigh 8-bitsare removed from the location

address bySP+1, atSP-2, thenSPisincremented by 2

STACK MEMORY ADDRESSINGMICROPROCESSORS ADDRESSING MODES


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Figure 1+"SH BX - place the contents of BX onto a stack


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Figure 2+O+ CX removed data from the stack and

place them intoCX


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Normally a complete program is written as a set of subroutines

To execute a subroutine aCALLinstruction is used

CALLis similar to aprocedure callin a high-level language

When executed it pushes IP and the return segment (forFAR calls) onto the stack, then

executes a jump to the call address

Two types of CALLs can be executed

CALLto aNEARaddress Only Offset (IP) specified, segment assumed to be the same

CALLto aFARaddress New Segment and Offset (IP) specified

CALLsubroutine is terminated with aRETinstruction

RET(RETurn) instruction causes the CPU to pop the RETURN address off the stack (IP

or Segment and IP) and execute a jump back to it

CALL ##

CALL #&8(##

CALLING SUBROUTINESMICROPROCESSORS ADDRESSING MODES


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If the subroutine is situated in the same segment

as the routine that it has been called from, then

the subroutine is considered to beNEAR.

If the subroutine is not situated in the same

segment as the routine that it has been called

from, then the subroutine is considered to be

FAR.

Jump to a location out of the current code segment,

meaning that not only IP but also CS is replaced with

new values

FAR VS NEAR SUBROUTINE

DIRECTIVESMICROPROCESSORS ADDRESSING MODES

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Micro 133 Prelim Lecture 4 - Microprocessor_s Addressing Modes

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