Instruction addressing and execution

Chapter 2Instruction Addressing and Execution

Recalling main concepts

Recalling main concepts

Recalling main concepts

• Segment: special areas defined to contain CODE, DATA and STACK• Paragraph boundary: location evenly divisible by 16

or 10H

Recalling main concepts

Stack Segment

Data Segment

Code Segment

SSDSCS

Segment Registers

Types of programs

• *.COM and *.EXE files• *.COM: consists of one segment containing code, data

and stack• *.exe: separate code, data and stack segments

Loading *.exe program• Access *.exe from disk• 256-byte Program Segment Prefix (PSP) on a

paragraph boundary• Store the program immediately following the PSP• Load address of PSP in the DS & ES• Load code segment in CS, set IP • Load address of the stack to SS, set SP• Transfer control to the program for execution

.model small,

.stack

.datamessage db "Hello everybody! I am learning assembly

language!","$"

.code

main proc mov ax, seg message mov ds,ax mov ah,09 lea dx,message int 21h mov ax,4c00h int 21hmain endpend main

Assembly directive to

define memory

model to use in the

program

Real and Protected mode

Real Mode 16-bit Protected

Mode

32-bit Protected Mode

Segment base address

20-bit24-bit,

from descriptor

32-bit,from descriptor

Segment size (limit)

16-bit, 64K bytes (fixed)

16-bit, 1-64K bytes

20-bit, 1-1M bytes or 4K-4G bytes

Segment protection

no yes yes

Segmentregister

segment base address / 16

selector selector

Protected mode-Is a type of memory utilization, available on Intel 80286 and later

-Support:protection: each program is protected

from interference from other programs. extended memory : Enables a single

program to access more than 640K of memory. virtual memory : Expands the address

space to over 1GB. Multitasking:

Booting processWhat is booting?

• The process of starting or restarting a computer

cold boot

Process of turning on a computer after it

has been powered off completely

warm boot

Process of restarting a

computer that is already powered on

Also called a warm start

Booting processHow does a personal computer boot up?

processor

BIO

S

hard disk

CD-ROM drive

(RAM) memory modules

CMOS

floppy disk drive

Step 6

expansion cards

BIOS Boot process

BIOS routineFFFF0H

Interrupt VectorTable

BIOS Data Areas

Access the bootstrap

loader

Check portsInitialize devices

.model small,

.stack

.datamessage db "Hello everybody! I am learning assembly

language!","$"

.code

main proc mov ax, seg message mov ds,ax mov ah,09 lea dx,message int 21h mov ax,4c00h int 21hmain endpend main

Assembly directive to define stack to use in the

program

STACK

• The word is from data structure• Last In, First Out (LIFO) mechanism• STACK in OS has three main functions:• Contains return address • Data• Content of present registers

STACK

• PUSH• Decrease SP by 2 and store a value there

• POP• Return a value from stack and increase SP by 2

Lesson plan

• Review loading an *.exe file• Concept of execution of instructions• Practice:

• Execution of instructions

Access *.exe from disk256-byte Program Segment Prefix (PSP) on a paragraph boundaryStore the program immediately following the PSPLoad address of PSP in the DS & ESLoad code segment in CS, set IP Load address of the stack to SS, set SPTransfer control to the program for execution

Loading *.exe file

Loading *.exe file

• The sequence of segments (code, data, and stack) is given• SS: contains the address of the beginning of the

stack• CS: contains the address of the beginning of the

code segment• DS: contains the address of the beginning of the

data segment• SP: contains the size of stack

Practice2B360H

PSP

Stack Segment

Data Segment

Code Segment

Memory

Practice2B360H

PSP

Stack Segment

Data Segment

Code Segment

Memory

PSP 2B360HPSP size 100HOffset 0HSS 2B460H

(stored as 2B46)

2B46HSS

Practice

2B360H

PSP

Stack Segment

Data Segment

Code Segment

Memory

2B46HSS

PSP 2B360HPSP size 100HOffset 30H

70HCS 2B500H (stored as 2B50)

CS 2B50H

Practice

2B360H

PSP

Stack Segment

Data Segment

Code Segment

Memory

2B46HSS

CS 2B50H

2B36H

2B36H

DS

ES

SP 0030H

Instruction Execution and Addressing

• Executing an instruction include• Fetch the next instruction, put to a queue (QUEUE: FIFO

vs. STACK LIFO)• Decode the instruction• Execute the instruction

Example

4AF0CS 0013IP

4AF13H

CS segment address: 4AF00HIP offset: 0013H________________________

+

Instruction address:

04B1DS

Example

4AF0CS 0013IP

4AF13H

A01200

Memory

04B1DS

Decode instruction:

AO: MOV [0012] to AL

Example

4AF0CS 0013IP

4AF13H

A01200

Memory

04B1DS

DS segment address:04B10HIP offset: 0012H________________________

+

Data address: 04B22H

Example

4AF0CS 0013IP

4AF13H

A01200

Memory

04B1DS

04B22Data address:

04B22H

| 1B

AXAX

AH AL

1B

Practice

• Viewing memory location using DEBUG

At DOS prompt, type: DEBUG• Checking Serial and parallel port:

D 40:00• Checking system equipment

D 40:10

Practice

• Viewing memory location using DEBUG

At DOS prompt, type: DEBUG

• Checking Serial and parallel port:

D 40:00

• Checking system equipment

D 40:10

Practice

• Viewing memory location using DEBUG

At DOS prompt, type: DEBUG

• Checking Serial and parallel port:

D 40:00

• Checking system equipment

D 40:10

22 C8 C822

reverse

Number of parallel printer ports=11(binary)=3 (15,14)

Number of serial ports=100(binary)=4 (11-9)

Number of diskette devices=00(binary)=1 (7,6)

Initial video mode =10 (5,4) (80x25 color)

Coprocessor present: 1 (1)Diskette drive is present: 0 (0)

Practice (cont.)

• Checking the keyboard status• D 40:17 (With Numlock and Caplock)

• Checking video status• D 40:49• D 40:84

Practice (cont.)

• Checking copyright notice & serial number• D FE00:0

• Checking ROM BIOS dateD FFFF:5

Practice (cont.)

Running the first assembly program step by step using EMU 8086