X86 assembly language - Notes from real mode to protected mode

Segment address ： offset

16  Bit register

General registers

• AX  accumulator （Accumulator）

• BX  Base register （Base Address Register）

• CX  Counter （Counter）

• DX  data （Data） register

• SI  Source index register （Source Index）

• DI  Target index register （Destination Index）

• BP  Base pointer register  (Base Pointer)

• SP  Stack register  (Stack Pointer)

Segment register

• Code segment （Code Segment,CS）

• Data segment （Data Segment,DS）

• Additional segment （Extra Segment, ES）

• Stack segment  （Stack Segment,SS）

Pointer register

• IP： Instruction pointer （Instruction Pointer）

20  Physical address of bit ：1MB  Of memory

16  Bit segment address  << 4 + 16  Bit offset address

• Arithmetic logic unit  (arithmetic and logic unit) ALU

Professional terms

• Dynamic random access memory （Dynamic Random Access Memory,DRAM）

• read-only memory （Read Only Memory,ROM）

• floppy disk （Floppy Disk）

• Hard disk （Hard Disk,HDD）

• “ turn / minute ”（Round Per Minute,RPM）

• Magnetic track （Track）

• cylinder （Cylinder）

• A sector （Sector）

• Master boot record （Master boot record, Abbreviation for MBR）

• Main boot sector :  The first sector is 0 Noodles 0 Avenue 1 A sector , Or rather, 0 head 0 column 1 A sector

• virtual machine （Virtual Machine,VM）

Main guide fan

• Main boot sector （Main Boot Sector,MBR）

• Display memory （Video RAM：VRAM）, abbreviation  
  memory

Computer startup

• Electrify

• Read ROM Inside BIOS, Used to check the hardware

• Hardware check passed

• BIOS According to the specified order , Check the first sector of the boot device （ Master boot record ）, Load in memory address  0x7C00

• The master boot record gives the operation right to the operating system

at that time , The matching operating system is

86-DOS

. This operating system requires at least 32KB. We know , Memory address from 0x0000 Numbered starting ,32KB Your memory is

0x0000～0x7FFF

.

8088 The chip itself needs to occupy

0x0000～0x03FF

, For preservation

Various interrupt handlers

Storage location of .（ The master boot record itself is an interrupt signal INT 19h Processing program .） therefore , There's only... Left in memory

0x0400～0x7FFF

have access to .

** In order to leave as much continuous memory as possible for the operating system , The master boot record is placed at the end of the memory address .** Because a sector is 512 byte , The master boot record itself generates data , Need to set aside 512 Byte save . therefore , Its reserved position becomes ：

0x7FFF - 512 - 512 + 1 = 0x7C00


After the computer starts ,32KB The memory usage is as follows .

+--------------------- 0x0| Interrupts vectors+--------------------- 0x400| BIOS data area+--------------------- 0x5??| OS load area+--------------------- 0x7C00| Boot sector+--------------------- 0x7E00| Boot data/stack+--------------------- 0x7FFF| (not used)+--------------------- (...)

Display text on screen

The display principle of characters on the screen

The mapping of video memory to memory in text mode

80×25 Text mode for . In this mode , The screen can show 25 That's ok , Each row 80 Characters , A total of... Per screen 2000 Characters .

0xB8000～0xBFFFF

  This physical address space , It's for the graphics card

Initialize segment register

label

lst  List file

Pseudo instruction （pseudo Instruction）

• DB:  Declaration byte （Declare Byte）

• DW（Declare Word） Used to declare word data

• DD（Declare Double Word） Used to declare double words （ Two words ） data

• DQ（Declare Quad Word） Used to declare quadword data

8086 Addressing mode of processor

• Register addressing

• Address immediately

• Memory addressing

• Direct addressing

• Base addressing

• BX

• BP

• Addressing

• SI

• DI

• Base addressing

Access and control of hard disk and graphics card

Declare constants （const）:  Do not occupy any assembly address

equ


port

in
out