(1)ffffh
(2)
assume cs:code
code segment
;编写7ch中断例程的安装
start:
mov ax,cs
mov ds,ax
mov si,offset dot
mov ax,0
mov es,ax
mov di,200h
mov cx,offset dotend-offset dot
cld
rep movsb
;设置7ch中断例程的中断向量
mov ax,0
mov es,ax
mov word ptr es:[7ch*4],200h
mov word ptr es:[7ch*4+2],0
mov ax,4c00h
int 21h
;编写7ch中断例程
dot:
push bp
mov bp,sp
add [bp+2],bx
pop bp
iret
dotend:
nop
code ends
end start