m p lab presentation

8/9/2019 M P Lab Presentation

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T. Krishna Chaitanya

Micro Processors Lab Demo


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Assembly Language Today

A program written directly in assembly language has thepotential to be smallerand to run fasterthan a HLL program

But it takes too long to write a large program in assemblylanguage

Only time-critical procedures are written in assemblylanguage (optimization for speed)

Assembly language are often used in embedded systemprograms stored in PROM chips

Computer cartridge games, micro controllers,

Assembly Language is a low level programming language


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General Purpose Registers

8086 CPU has 8 general purpose registers, each register has its own name:

AX - the accumulator register (divided into AH / AL).

BX - the base address register (divided into BH / BL).

CX - the count register (divided into CH / CL).

DX - the data register (divided into DH / DL).

SI - source index register.

DI - destination index register.

BP - base pointer.

SP - stack pointer.


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Segment Registers

CS - points at the segment containing the current program.

DS - generally points at segment where variables are defined.ES - extra segment register, it's up to a coder to define its usage.

SS - points at the segment containing the stack.


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8086 Instruction - Basic Structure

Label Operator Operand[s] ;Comment

Label- optional alphanumeric string1st character must be a-z,A-Z,?,@,_,$Last character must be :

Operator- assembly language instructionmnemonic: an instruction format for humansAssembler translates mnemonic into hexadecimal opcodeexample: mov is f8h

Operand[s]- 0 to 3 pieces of data required by instructionCan be several different formsDelineated by commasimmediate, register name, memory data, memory address

Comment- Extremely useful in assembler language

These fields are separated by White Space (tab, blank, \n, etc.)


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8086 Instruction - Example

Label Operator Operand[s] ;Comment

INIT: mov ax, bx ; Copy contents of bx into ax

Label - INIT:Operator - movOperands - ax andbx

Comment - alphanumeric string between; and \n

Not case sensitive

Unlike other assemblers, destination operand is firstmov is the mnemonicthat the assembler translates into an

opcode


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Assembler Language Segment Types

Stack

For dynamic data storage

Source file defines size

Must have exactly 1

Data

For static data Storage

Source file defines size

Source file defines content (optional)

Can have 0 or more

Code

For machine Instructions

Must have 1 or more


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x86 Instruction Type Classifications

DATATRANSFER

General mov ax, [DA T1] ;ax gets contents of mem

Strings cmpsb ;if DS:SI=ES:DI then ZF=1

Special Purpose xchg ax, bx ;ax gets bx and bx gets ax

ARITHMETIC/LOGIC

Integer add ax, bx ;ax gets ax+bx

ASCII, BCD aaa ;changes ASCII # to int.

Floating Point fadd DA T ;ST get ST+DAT

Logical and ax, bx ;ax gets ax A ND bx

Shifting ror ax, 2 ;ax contents shifted-2 right CONTROL TRANSFER

Branching jnz LABEL1 ;if ZF=1 then IP=LABEL1

Interrupt int 21h ;invoke INT handler 21h

Subroutine call SUB1 ;invoke subroutine, SUB1

Modify Flag cli ;IF gets zero

Halt Processor hlt ;need R ESET to run again

No Operation nop ;


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Data Transfer Instructions

MOV target, source

reg, reg mem, reg

reg, mem

mem, immed

reg, immed

Sizes of both operandsmust be the same

reg can be any non-

segment registerexcept IP cannot be the

target register

MOV's between a

segment register and

memory or a 16-bitregister are possible


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DataAllocation Directives

db define byte

dw define word (2 bytes)dd define double word (4 bytes)

dq define quadword (8 bytes)

dt define tenbytes

equ equate, assign numeric expression to a name

Examples:

db 100 dup (?) define 100 bytes, with no initial values for bytes

db Hello define 5 bytes, ASCII equivalent of Hello.


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Sample MOV Instructions

b db 4Fh

w dw 2048

mov bl,dh

mov ax,w

mov ch,b

mov al,255mov w,-100

mov b,0

When a variable is created with a

define directive, it is assigned adefault size attribute (byte, word,

etc)

You can assign a size attribute

using LABEL

LoByte LABEL BYTE

aWord DW 97F2h


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MOVAX, 0B800h ; setAX to hexadecimal value of B800h.

MOV DS,AX ; copy value ofAX to DS.

MOV CL, 'A' ; set CL toASCII code of 'A', it is 41h.

MOV CH, 1101_1111b ; set CH to binary value.

MOV BX, 15Eh ; set BX to 15Eh.

MOV [BX], CX ; copy contents of CX to memory at B800:015E

RET ; returns to operating system.


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eXCHanGe

XCHGtarget, source

reg, reg reg, mem

mem, reg

MOV and XCHG

cannot perform memory

to memory moves

This provides an

efficient means to swapthe operands

No temporary storage is

needed

Sorting often requires

this type of operation This works only with the

general registers


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Arithmetic Instructions

ADD dest, source

SUB dest, sourceINC dest

DEC dest

NEGdest

Operands must be ofthe same size

source can be a

general register,memory location, or

constant

destcan be a register

or memory location

except operands cannotboth be memory


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Program Segment Structure

Data Segments

Storage for variables Variable addresses are

computed as offsets from

start of this segment

Code Segment

contains executableinstructions

Stack Segment

used to set aside storagefor the stack

Stack addresses are

computed as offsets into

this segment

Segment directives.data.code

.stack size


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Program Skeleton

.model small

.stack 100H

.data;declarations

.codemain proc

;codemain endp

;other procsend main

Select a memory model

Define the stack size Declare variables

Write code organize into procedures

Mark the end of the

source file optionally, define the entry

point


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Write programme on the screen


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eg: File name: [ d:\ add.asm..]


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Next step is to create executable file using the linker:


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This causes linker to create: ADD.EXE


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Press F 7


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Press F 7


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Press F 7


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Press F 7


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Press F 7


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Press F 7


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;add two 8-bit numbersdata segment

addend db 20h

adder db 10h

sum db ?

data ends

code segment

assume cs:code, ds:data

start: mov ax,data ;

mov ds,ax ;ds


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data segment

n dw 5

res dw ?

data ends

code segment

assume cs:code,ds:data

mov ax,data

mov ds,ax

mov ax,n

sub ax,1mov bx,ax

add ax,1

yy: mul bx

dec bx

jz down

loop yydown:mov res,ax

mov ax,4c00h

int 21h

code ends

end


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Next step is to create executable file using the linker:


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This causes linker to create: ADD.EXE


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Press F 7


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Press F 7


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Press F 7


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Press F 7


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Press F 7


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Press F 7


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;add two 8-bit numbersdata segment

addend db 20h

adder db 10h

sum db ?

data ends

code segment

assume cs:code, ds:data

start: mov ax,data ;

mov ds,ax ;ds


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data segment

n dw 5

res dw ?

data ends

code segment

assume cs:code,ds:data

mov ax,data

mov ds,ax

mov ax,n

sub ax,1mov bx,ax

add ax,1

yy: mul bx

dec bx

jz down

loop yy

down:mov res,ax

mov ax,4c00h

int 21h

code ends

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