我用DEBUG跟踪以下程序
assume cs:codesg                                                           
codesg segment                                                             
   mov  ax,2000h                                                           
   mov  ss,ax                                                              
   mov  sp,0                                                               
   add  sp,4                                                               
   pop  ax                                                                 
   pop  bx                                                                 
   push ax                                                                 
   push bx                                                                 
   pop ax                                                                  
   pop bx                                                                  
   mov  ax,4c00h                                                           
   int  21h                                                                
codesg ends                                                                
end                                                                        
                                                                           
                                                                             当执行POP AX的时候报错，内容为
NIVDM CPU 遇到无效指令
CS：0000 IP：0077 OP：F0 37 05 14 02
难道我的代码是错误的吗？此代码编译出的*。EXE文件是可以执行的啊
哪为大哥能指点一下小弟啊~！！！