DF标志和串传送指令(1105)

本文为《汇编语言程序设计》1105小节例程。点击链接…进课程主页。

编程：将data段中的第一个字符串复制到它后面的空间中。

   data segment
        db 'Welcome to masm!'
        db 16 dup (0)
   data ends

程序：

code segment
start: mov ax,data
         mov ds,ax
         mov si,0
         mov di,16
         mov cx,8
    s:  mov ax,[si]
         mov [di],ax
         add si,2
         add di,2
         loop s

         mov ax,4c00h
         int 21h
code ends
end start

用串传送指令

assume cs:code, ds:data
data segment
    db 'Welcome to masm!'
    db 16 dup (0)
data ends
code segment
start:
   mov ax,data
   mov ds,ax
   mov si,0
   mov es,ax
   mov di,16
   mov cx ,16
   cld
s: movsb
   loop s

   mov ax,4c00h
   int 21h
code ends
end start

另外一个功能相同的程序

assume cs:code, ds:data
data segment
    db 'Welcome to masm!'
    db 16 dup (0)
data ends
code segment
start:
   mov ax,data
   mov ds,ax
   mov si,0
   mov es,ax
   mov di,16
   cld
   mov cx,8
   rep movsw

   mov ax,4c00h
   int 21h
code ends
end start

用rep指令重复串传送
任务：用串传送指令，将F000H段中的最后16个字符复制到data段中。

assume cs:code, ds:data
data segment
   db 16 dup (0)
data ends
code segment
start:
     mov ax,0f000h
     mov ds,ax
     mov si,0ffffh
     mov ax,data
     mov es,ax
     mov di,15
     mov cx,16
     std
     rep movsb

     mov ax,4c00h
     int 21h
code ends
end start