中断程序的编写步骤：主程序：(1)设置中断向量(DOS调用AH=25H)(2)设置CPU中断允许位FLAGS中的IF位=1允许中断（STI开中断）=0禁止中断（CLI关中断）(3)设置中断屏蔽位I/O端口21H中断屏蔽寄存器中断屏蔽位=0允许中断=1禁止中断76543210中断程序设计：datasegmentmessdb‘itis',0AH,0DH,'$'dataendscodesegmentassumecs:code,ds:datastart:movax,seg中断子程序movds,axmovdx,offset中断子程序moval,0fh;设中断程序的类型号为0fhmovah,25hint21hcli;清中断标志位inal,21h;读中断屏蔽寄存器（21H为中断屏蔽寄存器）andal,7fh;开放IRQ7中断（0为开放中断）out21h,alsti;置中断标志位delay:jmpdelayint7:………….moval,20hout20h,al;发出EOI结束中断…………..inal,21horal,80h;关闭IR7中断out21h,alsti;置中断标志位movah,4ch;返回DOSint21hnext:iretcodeendsendstart7