 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] SMS: B08632      ]
 ] S. SMITH           ]    BFS PROGRAM NOTE         ]                  ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE:            ]
 ] RI/DNY/3701        ]      RELEASE NOTE ( )       ] 09/10/86         ]
 ]                    ]                             ] REV: 06/01/88    ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] OI76 & SUBS                   ]  CREW ( )  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]           MAJOR SOFTWARE AREA:            ] OPS MODES AFFECTED:     ]
 ]BSL( ) BSS(X) GNC( ) SEQ( ) SM/SP( ) IPL( )]1,3,6                    ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: BOS, GPC, BCE, COMMFAULTS                        ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: MG038101/3.1.8                                 ]
 ]_____________________________________________________________________]
 ] TITLE: ILLEGAL OPCODE LSN ERROR                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ]                                                                     ]
 ]  WHEN BFS IS TRACKING PASS AND PASS TRANSITIONS TO OPS 2 OR 9, BFS  ]
 ]  WILL RECEIVE HFE LISTEN ERRORS FOR 2 CONSECUTIVE MINOR CYCLES      ]
 ]  BEFORE GOING STANDALONE. THE I/O ERROR LOG ENTRIES WILL INDICATE   ]
 ]  THE BCE STATUS REGISTER CONTAINS ZERO. DURING THE PASS TRANSITION A]
 ]  LISTEN COMMAND IS SENT ACROSS THE FLIGHT CRITICAL BUSES, FOR HOUSE-]
 ]  KEEPING PURPOSES, WHICH BFS DOES NOT EXPECT.  PASS/BFS TIMING IS   ]
 ]  SUCH THAT THE COMMAND IS NOT ALWAYS SEEN BY BFS. WHEN IT IS SEEN   ]
 ]  BFS GUARDS AGAINST EXECUTING UNEXPECTED LISTEN COMMANDS BY FORCING ]
 ]  THE BCE'S TO EXECUTE AN ILLEGAL INSTRUCTION.  THE CONTENTS OF THE  ]
 ]  BCE STATUS REGISTER WILL HAVE THE "ILLEGAL OPCODE" BIT SET FOR THE ]
 ]  LAST GROUP OF HFE LISTEN ERRORS LOGGED.                            ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]USER RESPONSE:                                                       ]
 ]                                                                     ]
 ]                  NONE                                               ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]RI: <S> C. PURTELL        DATE 06/03/88]                             ]
 ] --------------------         ---------]                             ]
 ]SSD: SAM ANKNEY           DATE 07/13/88]                             ]
 ] --------------------         ---------] JACK BOYKIN        08/17/88 ]
 ]PF MGR: MICHAEL BRIEDEN   DATE 08/05/88]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_____________________________________________________________________]
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