BPLxDAT

         The Amiga hardware is currently able to display
         eight bitplanes.  These registers are typically
         written to by the bitplane DMA, but they may also be
         written to by the programmer directly.  The parallel
         data from the six bitplanes is shifted out the left
         and converted to a color.  BPL1DAT is the trigger
         register.  That means that you should write to
         BPL2DAT - BPL8DAT first, then write to BPL1DAT to
         trigger the serial conversion.


          BPL1DAT   Bitplane DMA trigger.  Color Weight = 1
          BPL2DAT   Weight = 2
          BPL3DAT   Weight = 4
          BPL4DAT   Weight = 8
          BPL5DAT   Weight = 16
          BPL6DAT   Weight = 32
          BPL7DAT   Weight = 64
          BPL8DAT   Weight = 128