1 assume cs:code
2 //奇怪之处ax的值为47h?使用指令pushf,popf
3 code segment
4 start:
5 mov ax,0
6 push ax
7 popf //从栈中弹出数据,送入标志寄存器,易知PSW将会被置为0
8 mov ax,0fff0h
9 add ax,0010h //结果为0000h,并发生进位,不溢出,此时寄存器的状态为NV UP DI PL ZR NA PE CY(即PSW:00000000 01000111,如果默认第01位为0则是01000101结果为45)
10 pushf //将psw=47h值压入栈
11 pop ax //将之前压入的值赋给al=47h(01000111)ah=0h(00000000)
12 and al,11000101b //异与后al=45h(01000101)ah不变
13 and ah,00001000b //异与后ah=0h(00000000)al不变
14 mov ax,4c00h
15 int 21h
16 code ends //所以ax最后值为45h
17
18 end start
