X0                                                                                
-------------------------------I  I-----------------------------------------------------------------[  PLS    M10   ]
                                   启动    



                     M10          M20
------------------I  I-----------I / I-------.-------------------------------------------------------------(   M20  )
                                       启动      I                                                                             启动                                                              
                                                    I                                                                          
                                                    I
                                                    I
                                                    I
                     M10           M20      I
------------------I / I------------I  I------'  
                                       启动                                                          

                            是已验证过的程序，写出来，与大家共享。

感谢楼主！