Sequence Regsiter Usage 

    Number     Use
     0-13    Local Registers
    14-15    Copy of Sequence ID
    16-26    Global Registers
    27-47    Build In variables

      48       Spare

      49     Block Repeat Count
    50-53    Small Buffer Lock Status  

    54-99      Spare
   
   100-159   Execute List
     100       Delay Between Frames
     101       Delay Between Repoints
     102-0     Pause if $SAA set
     102-1     Exit if $SAA set
     102-2     Exit if $FLR set
     102-3     Exit if $SFL set
     105       Number of Frames
  106 - 121    Frame ID's
     125       Number of Targets
  126 - 159    Target ID's (16 bit?)

  160 - 239    Spare

  239 - 247    Used by Sequence Code
  248 - 255    Used by Compiler