Assembly language segment definition

Link to the original text —— SevenOne’Blog

Three steps for segment definition

Segment definition

1. keyword ：segment( Start ) ends( end )

2. Paragraph name ： No more than eight characters . In general ,

   • code Represents a code snippet .
   • data Represents a data segment

3. grammar

    Paragraph name  segment
   
    Paragraph name  ends
   

Segment Association

1. keyword ：assume

2. type ：CS（ Code segment ）、DS（ Data segment ）、SS（ stack segment ）、ES（ Additional segment ）

3. grammar ：

   assume  type : Paragraph name 
   

4. example ： Define a code snippet code, Define a data segment data

   code segment
   	assume cs:code,ds:data
   code ends
   
   data segment
   
   data ends
   

Segment transmission

1. Transfer is to transfer the data in the segment to the specified segment register . for example , speak data The data in is transmitted to DS In data segment , There is no real transfer of data during Association .

2. Code segments do not need segment transfer when defining , Other segments need to be transferred manually .

3. adopt mov Segments cannot be passed directly to segment registers , It can be transmitted indirectly .

   ……
   mov ax,data
   mov ds,ax
   ……
   

   This code means , Will now data Save the data segment to ax in , then ax Save the data in to ds in .

Data segment

Pseudo instructions for opening up space

1. db： Open up a byte space .
2. dw： Open up a word space .（ Two bytes ）
3. dup： Cycle to store characters

Store the data

1. Storage 10 Hexadecimal data , Direct write .
2. When storing character data, use single quotation marks , In the end in debug In this mode, the real thing is this character ASCII code 16 Base representation .

Grammar format

1. No address symbol

   

2. With address symbols

   

Code demonstration

1. Use db Definition 5 An odd number , Save the first number to AH in , The last number is saved to AL in .

   

   Final ,AX=0109, Exactly AH And AL The joining together of .

2. Use dw Definition 5 An odd number , Deposit in AX in .

   

3. utilize dup Open up three single byte spaces

   data segment
       str db 3 dup(5)
   data ends
   code segment
       assume cs:code,ds:data
       main:
           mov ax,data
           mov ds,ax
           
       edit:
           mov ah,4ch
           int 21h
   code ends
       end main