编写安装中断7ch的中断例程：将一个以0结尾的字符串，转化为大写

中断的安装程序：

assume cs:code

code segment
start:
    mov ax, cs
    mov ds, ax
    mov si, offset chstr

    mov ax, 0
    mov es, ax
    mov di, 200h
    mov cx, offset chstrend - offset chstr
    cld
    rep movsb

    mov ax, 0
    mov es, ax
    mov word ptr es:[7ch * 4 + 0], 200h
    mov word ptr es:[7ch * 4 + 2], 0

    mov ax, 4c00h
    int 21h

chstr:
    mov si, 0
lh:
    mov cx, 0
    mov cl, [si]
    jcxz ok
    and byte ptr [si], 11011111b
    inc si
    jmp lh
ok:
    iret

chstrend:
    nop

code ends

end start

测试程序：

assume cs:code,  ds:data

data segment
    db 'conversation', 0
data ends

code segment
start:
    mov ax, data
    mov ds, ax
    mov si, 0
    int 7ch
    
    mov ax, 4c00h
    int 21h
code ends

end start

其实都是一个思路……

这货不难。