CERC Trigger Flow:
------------------

External Trigger                    Enabled by DB Reg 1 bit 0
      +
DB Serial Trig                      Issued by DB Serial Command

=  DB Trigger

--- LVDS via Backplane DB->BE ---

=  BE External Trigger              Enabled by BE Reg 1 bit 0
         +
   BE Oscillator Trigger            Enabled by BE Reg 1 bit 1
         +
   BE Serial Trig                   Issued by BE Serial Command

   =  BE Trigger                    Reset by BE Reg 0

   =  BE Trigger to FEs             Enabled by BE Reg 4 bits 0-7

   --- LVDS on board BE->FE ---

      =  Trigger Input              Enabled by BE Reg 1
               +
         FE Serial Trig             Issued by FE Serial Command

         =  FE Trigger