;功能：安装一个新的int7ch中断例程，实现一个子程序 setScreen ，提供如下功能：
; （1）清屏。
; （2）设置前景色。
; （3）设置背景色。
; （4）向上滚动一行; 入口参数说明：
; （1）每个子程序用 ah 寄存器传递功能号：
; （2）对于2、3号功能，用al传送颜色值，

assume cs:code,ds:datadata segment  err db '   ~~~~~ ah args is error! ~~~~~','$'init dw 10 dup(0)data endscode segmentstart:mov ax,datamov ds,axmov ax,0mov es,axmov ax,es:[7ch*4]mov init[0],axmov ax,es:[7ch*4+2]mov init[1],axmov es:[7ch*4],offset setScreenmov es:[7ch*4+2],csmov ax,102hint 7ch;call breakPointmov ax,201hint 7ch;call breakPointmov ax,300hint 7ch;call breakPointmov ax,0hint 7chmov ax,400hint 7chmov ax,0mov es,axmov ax,datamov ds,axmov ax,init[0]mov es:[7ch*4],axmov ax,init[1]mov es:[7ch*4+2],axok: mov ax,4c00hint 21hsetScreen:jmp short setmainlist dw sub0,sub1,sub2,sub3setmain:cmp ah,3ja subErrmov bl,ahmov bh,0shl bx,1call word ptr list[bx]iretsub0:    ;清屏mov cx,0b800hmov es,cxmov cx,2000mov bx,0sub0s:mov byte ptr es:[bx],' 'add bx,2loop sub0sretsub1:    ;设置前景色。mov cx,0b800hmov es,cxmov cx,2000mov bx,1sub1s:and byte ptr es:[bx],11111000bor es:[bx],aladd bx,2loop sub1sretsub2:    ;设置背景色。mov cx,0b800hmov es,cxmov cx,2000mov bx,1shl al,1shl al,1shl al,1shl al,1sub2s:and byte ptr es:[bx],10001111bor es:[bx],aladd bx,2loop sub2sretsub3:    ;向上滚动一行mov cx,0b800hmov es,cxmov ds,cxmov di,0mov si,160climov cx,24sub3s:push cxmov cx,160rep movsbpop cxloop sub3smov cx,160mov bx,0sub3s1:mov byte ptr es:3840[bx],' 'add bx,2loop sub3s1retsubErr:    ;显示错误信息mov ax,datamov ds,axmov ah,9mov dx,offset errint 21hjmp okbreakPoint:    ;设置断点，用于调试pushfpop bxor bh,3push bxpopfretcode endsend start