 +_____________________________________________________________________
  AUTHOR:                                          SMS:  B20051     
    KEN KRESSIN          BFS PROGRAM NOTE          DR:   106208     
 ____________________                             __________________
  ORG/PHONE:          OPS NOTE (X)  USER NOTE ( )  DATE: 5/22/91    
   RID/(213)922-2146       RELEASE NOTE ( )                         
 ___________________________________________________________________
  OI/FLIGHT EFFECTIVITY:          USER AFFECTED:                     
    OI-20, OI-21, OI-22           CREW (X)  GROUND ( )  DUMP ONLY ( )
 ____________________________________________________________________
            MAJOR SOFTWARE AREA:             OPS MODES AFFECTED:     
 BSL( ) BSS(X) GNC( ) SEQ( ) SM/SP( ) IPL( )      0, 1, 3, 6         
 _____________________________________________________________________
  SOFTWARE SUB-AREA: DISP                                             
 _____________________________________________________________________
  PRINCIPAL FUNCTIONS: STS83-0020/3.5                                 
 _____________________________________________________________________
  TITLE:                                                              
             D&C BUFFER NOT INITIALIZED BY SYS RESET                  
 _____________________________________________________________________
  DESCRIPTION:                                                        
   CRT DISPLAY CONTROL (CDC) BUFFERS CONTAIN INFORMATION ABOUT THE BFS
   DISPLAYS SUPPORTED ON THE DEU'S.  ONE CDC BUFFER IS USED FOR EACH  
   DISTINCT DISPLAY.  AS LONG AS FOUR CDC BUFFERS ARE AVAILABLE, FOUR 
   DISTINCT DISPLAYS CAN BE SUPPORTED. IF THE NUMBER OF USABLE CDC'S  
   IS REDUCED, SO IS THE NUMBER OF DISTINCT DISPLAYS THAT BFS CAN     
   SUPPORT.                                                           
                                                                      
   THE NUMBER OF USABLE CDC'S IS REDUCED WHENEVER THE BFS CONTROLLED  
   DEU(S) IS NOT DEASSIGNED PRIOR TO PLACING THE BFS IN HALT.  WHEN   
   THE BFS IS SUBSEQUENTLY SWITCHED TO STANDBY OR RUN (CAUSING A      
   SYSTEM RESET), THE NUMBER OF USABLE CDC'S WILL BE REDUCED BY THE   
   NUMBER OF CDC'S WHICH WERE ACTIVE WHEN THE BFS WAS PLACED IN HALT. 
                                                                      
   IN THE CASE WHERE THE BFS IS SWITCHED TO HALT ON FOUR SEPARATE     
   OCCASIONS WHILE CONTROLLING ONE DEU, A SUBSEQUENT TRANSITION TO    
   STANDBY OR RUN WILL CAUSE A "STORE PROTECT" GPC ERROR AND THE LOSS 
   OF ALL DISPLAY CAPABILITIES AND COULD CAUSE THE OVERWRITING OF     
   VALID DATA WITH GARBAGE DATA.  SEE PAGE 2 FOR MORE INFORMATION.    
 _____________________________________________________________________
  USER RESPONSE:                                                      
    THE PROBLEM WILL BE AVOIDED IF THE BFS CONTROLLED DEU(S) IS       
    DEASSIGNED PRIOR TO PLACING THE BFS IN HALT.  THE DEU(S) CAN BE   
    DEASSIGNED BY TURNING THE BFC CRT SWITCH TO THE "OFF" POSITION    
    OR BY ENTERING THE APPROPRIATE GPC/CRT KEYSTROKE SEQUENCE.  IF    
    THE PROBLEM IS ENCOUNTERED, THE FOUR CDC BUFFERS WILL BECOME      
    AVAILABLE ONLY IF AN IPL IS PERFORMED ON THE BFS GPC.             
 _____________________________________________________________________
 CONCURRENCE:                           APPROVAL:                    
 RI: <S> C. PURTELL        DATE 06/26/91                             
     --------------------      ---------                             
 FDSD: W. R. PRUETT        DATE 07/09/91                             
      -------------------      --------- DARRELL E. STAMPER 07/10/91 
 PF MGR: D. STEPHENSON     DATE 07/10/91------------------- -------- 
        -----------------      --------- CHAIRMAN, SASCB      DATE   
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 +_____________________________________________________________________
                                                                      
                        SUPPLEMENTAL SHEET                            
                                                                      
 _____________________________________________________________________
  AUTHOR:                                          SMS:  B20051     
    KEN KRESSIN          BFS PROGRAM NOTE          DR:   106208     
 ____________________                             __________________
  ORG/PHONE:          OPS NOTE (X)  USER NOTE ( )  DATE: 5/22/91    
   RID/(213)922-2146       RELEASE NOTE ( )                         
 ___________________________________________________________________
  TITLE:                                                              
                                                                      
           D&C BUFFER NOT INITIALIZED BY SYS RESET                    
 _____________________________________________________________________
  DESCRIPTION:                                                        
                                                                      
   IN THE CASE WHERE THE BFS IS SWITCHED TO HALT ON TWO SEPERATE      
   OCCASIONS WHILE CONTROLLING ONE DEU, A SUBSEQUENT TRANSITION TO    
   STANDBY OR RUN WILL NOT CAUSE AN ERROR SINCE TWO CDC BUFFERS ARE   
   STILL AVAILABLE TO SUPPORT THE OPS DISPLAY.  IF, HOWEVER, SECOND   
   AND THIRD DEU'S ARE THEN ASSIGNED TO THE BFS AND IF SECOND AND     
   THIRD DISTINCT DISPLAYS ARE REQUESTED ON THOSE DEU'S, THEN NO CDC  
   BUFFER WILL BE AVAILABLE TO SUPPORT THE THIRD DISTINCT DISPLAY.    
   THE REQUEST FOR THAT DISPLAY WILL NOT BE PROCESSED AND A "STORE    
   PROTECT" GPC ERROR WILL OCCUR, BUT IN MOST CASES THE TWO DISTINCT  
   DISPLAYS WILL CONTINUE TO BE SUPPORTED ON THE THREE BFS CONTROLLED 
   DEU'S.  THE GPC ERROR WILL OCCUR ONCE FOLLOWING THE DISPLAY        
   REQUEST, AND WILL NOT CAUSE A SOFTWARE RESTART.  THE POSSIBILITY   
   OF OVERWRITING VALID DATA EXISTS IN THIS CASE ALSO.                
                                                                      
   ALL OTHER POSSIBLE SCENARIOS RESULT IN ONE OR MORE OF THE          
   CONSEQUENCES DESCRIBED ABOVE.                                      
                                                                      
                                                                      
                                                                      
 _____________________________________________________________________
  USER RESPONSE:                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
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