[Assembly language] by Wang Shuang | Experiment 12: Write a handler for interrupt No. 0

Preface: This experiment is experiment 12 (p251) in the third edition of "Assembly Language" written by Mr. Wang Shuang

Experimental environment: DOSBox 0.74-3

Experimental tasks:

        Write the handler for interrupt 0 , so that when the division overflow occurs, the string " divide error! " is displayed in the middle of the screen, and then returns to DOS.

        Requirements: Carefully track and debug, and do not study the following courses until you understand the whole process.

code:

assume cs:code

code segment
start: ;将do0段代码安装到0000:0200h处
       ;ds:si指向cs:offset do0
       ;es:di指向0000:0200h
       ;代码长度=offset do0end - offset do0start
       ;传送方向:正向
       mov ax,cs
       mov ds,ax
       mov si,offset do0
       mov ax,0
       mov es,ax
       mov di,200h
       mov cx,offset do0end - offset do0
       cld
       rep movsb
       
       ;设置中断向量表
       ;0号中断对应的中断向量表地址:0000:0000 ~ 0000:0003
       ;0000:0000字单元存储0000
       ;0000:0002字单元存储200h
       mov ax,0
       mov ds,ax
       mov word ptr ds:[0],200h
       mov word ptr ds:[2],0h

       ;除法溢出测试
       mov ax,1000
       mov bh,1
       div bh
 
       mov ax,4c00h
       int 21h

     do0: jmp short do0start
          db "divide error!"  
do0start: mov ax,0b800h
          mov es,ax
          mov di,12*160+36*2  ;设置es:di指向显示的显示缓存单元
          
          mov ax,cs
          mov ds,ax  ;字符串和代码数据都在一个段内:cs段
          mov si,202h  ;ds:si指向显示的字符串

          mov cx,13  ;设置字符串长度
       s: mov al,ds:[si]
          mov es:[di],al
          mov al,01000010b
          mov es:[di+1],al
          inc si
          add di,2
          loop s

          mov ax,4c00h
          int 21h

  do0end: nop

code ends
end start

operation result: