西門子程序

我搞不明白以下程序，請高手幫忙解答：BLD 7
                                                                        = L 26.0
                                                                       UC  SFC 64
                                                                        P#L27.0
                                                                        L     LD 27
                                                                       OPN  DB  491;
這程序是什麼意思？
還有==I是什麼意思？謝謝！