 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] SMS:  D027       ]
 ] P. WILSON          ]    BFS PROGRAM NOTE         ] DR:              ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE : 04/07/83  ]
 ] RI/KSC/1-4656      ]      RELEASE NOTE ( )       ] REV B: 12/05/95  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] ALL                           ]  CREW (X)  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]           MAJOR SOFTWARE AREA:            ] OPS MODES AFFECTED:     ]
 ]BSL( )BSS( )GNC( )SEQ( )SMSP( )IPL( )DCP(X)] ALL                     ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: DCP (DCP 8.07)                                   ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: MG017300                                       ]
 ]_____________________________________________________________________]
 ] TITLE: DEU POLL RESPONSE CHECKSUM ANOMALIES                         ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ]                                                                     ]
 ] PASS AND BFS ANNUNCIATE AN 'I/O ERROR CRT' FAULT MESSAGE (WITH NO   ]
 ] ASSOCIATED I/O ERROR LOG ENTRY) WHEN THE CHECKSUM IT RECEIVES FROM  ]
 ] THE DEU DOES NOT COMPARE WITH THE GPC COMPUTED CHECKSUM. DCP        ]
 ] ANALYSIS HAS DISCOVERED THAT THERE ARE TIMING WINDOWS OF 5, 28 AND  ]
 ] 239-420 MICRO-SECONDS IN WHICH THE POLL REQUEST PROCESSING CAN      ]
 ] INTERRUPT THE KEYBOARD PROCESSING SUCH THAT THE CONTENTS OF THE     ]
 ] "POLL RESPONSE" AND "POLLUTION" BUFFERS DIFFER, CAUSING DIFFERENT   ]
 ] CHECKSUMS. UNDER THIS CONDITION, THE DCP TRANSMITS THE "POLLUTION"  ]
 ] CHECKSUM, WHICH IS GUARANTEED TO BE DIFFERENT FROM THE CHECKSUM     ]
 ] COMPUTED BY THE GPC. PASS AND BFS VERIFY POLL RESPONSE CHECKSUMS    ]
 ] WHEN THE "MESSAGE PRESENT" BIT IS SET IN THE RESPONSE HEADERWORD.   ]
 ] THEREFORE, THIS CONDITION WILL ONLY BE ANNUNCIATED ON COMPLETE      ]
 ] KEYBOARD MESSAGES.                                                  ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] USER RESPONSE:                                                      ]
 ]                                                                     ]
 ] IGNORE THE FAULT MESSAGE. DEPRESS 'MSG RESET' AND RE-ENTER THE      ]
 ] KEYBOARD ENTRY.                                                     ]
 ]                                                                     ]
 ] FOR PASS, THE VARIABLE DMIB_ERR_MSG IS TYPICALLY ADDED TO THE       ]
 ] VARIABLE DOWNLIST AND, IF AVAILABLE, CAN BE USED TO VERIFY THE      ]
 ] CHECKSUM ERROR CONDITION. THIS VARIABLE WILL INDICATE THE FAILURE   ]
 ] CONDITION UNTIL A COMPLETE KEYBOARD MESSAGE IS RECEIVED WITH A      ]
 ] VALID CHECKSUM.                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]RI: <S> G. ALBRIGHT       DATE 01/23/96]                             ]
 ]    --------------------      ---------]                             ]
 ]ASD:   ERIC C. BINGHAM    DATE 02/06/96]                             ]
 ]    --------------------      ---------] DARRELL E. STAMPER 02/08/96 ]
 ]PF MGR:   M. C. KERR      DATE 02/07/96]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_____________________________________________________________________]
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