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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