Introduction to assembly language （1）

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1. Configure the compilation environment

1.1 Software download

1.1.1DOSBOX download

Enter the official website and select the corresponding version to download . Download path ：DOSBox, an x86 emulator with DOS

1.1.2 DEBUG、TASM、TLINK download

link ：https://pan.baidu.com/s/16Z8IeUGzgaJriKRItQ5oLw

Extraction code ：F777

1.2 Environment configuration

take debug、tasm、tlink After downloading, move to the same folder , If it is convenient, you can also set this folder as the program storage folder .

Then set the environment as follows ：

open dosbox, It will be as shown in the figure below . Then you can enter instructions on the command line

1.3 Generate exe file

1. To write .asm file , Or write .txt file , Then change the suffix to .asm

2. Enter the following command on the above command line , take .asm The documents are compiled as .obj file

   

3. Enter the following command again , Will make use of .obj File connection generation .exe file

   

2. Source program structure

	[.586]		; Select instruction set , Choose which CPU To perform 
DATA SEGMENT	;  Define data segments 
……				; Data definition pseudo instruction sequence 
DATA ENDS		
STACK SEGMENT	;  Define stack segments 
……				; Data definition pseudo instruction sequence 
STACK ENDS
CODE SEGMENT	; Define code snippets 
ASSUME CS:CODE,SS:STACK,DS:DATA; Segment register description , Code snippets are essential , It is convenient to list all the pictures directly 
START:				
	MOV AX,DATA		; Take the base address of the data segment 
	MOV DS,AX		; Establish addressability of data segment 
	……
	MOV AH,4CH		; return DOS operating system 
	INT 21H
CODE ENDS
	END START		; When the source program is the main module , Start label is required START

3. Common pseudo instruction statements

3.1 Logical segment definition pseudo instruction

1. Segment definition statement ：

   from SEGMENT Statements begin , To ENDS End of sentence .

2. Segment register description statement ：

   ASSUME Segment register ： Paragraph name

   Explain which register is used to address the segments defined in the source program

3. Set the initial value of the segment register

   1. Use SEG The operator finds the segment base address of the logical segment 
   MOV AX,SEG	DATA	;DATA Data segment name 
   MOV DS,AX
   2. Assign the segment name directly to the segment register 
   MOV AX,DATA
   MOV ES,AX
   

3.2 Data definition directives

1. Constant definition pseudo instruction

Don't allocate memory

1. Assignment pseudo instruction EQU

   Use EQU Pseudo instructions define symbolic constants , Its value cannot be changed later , That is equivalent to c Linguistic const

2. Equal sign pseudo instruction ——=

   Its symbolic name can be redefined , The definition statement can be placed in any logical segment

2. Variable definition pseudo instruction

DB/DW/DD Data item

1. DB It is to allocate a byte unit for each character from left to right
2. DW Assign a word unit for every two characters
3. DD Assign every four characters 1 Double word units

$$byWhenfrontThe\; earthsitemeterCountdeviceOfvalue,MeetingatakeWhenfrontInsidesaveThe\; earthsite$

3.3 Procedures and macros define pseudo instructions

1. Procedure definition directives

 The process of 	PROC  [ attribute ]
……
[RET]
……
RET
 The process of 	ENDP

Pass in the main program CALL call

2. Macro definition directives

 Macro name  MACRO [ Form parameter table ]
……
ENDM

The label in the macro body should be LOCAL Pseudo instructions are described as local labels , To avoid multiple calls , A definition error occurred ; Hongzhankai ,LOCAL The definition label is defined by ??0000 To ??FFFF To replace .

Main program passed CALL call

2. Macro definition directives

 Macro name  MACRO [ Form parameter table ]
……
ENDM

The label in the macro body should be LOCAL Pseudo instructions are described as local labels , To avoid multiple calls , A definition error occurred ; Hongzhankai ,LOCAL The definition label is defined by ??0000 To ??FFFF To replace .