This section summarizes the registers used in this chapter and the meaning
of their bit settings. The  color registers  are summarized in the next
section. See  appendix a  for a summary of all registers.

BPLCON0 - Bitplane Control

   (Warning: Bits in this register cannot be independently set.)

   Bit 0 - unused

   Bit 1 - ERSY (external synchronization enable)
      1 = External synchronization enabled (allows genlock
          synchronization to occur)
      0 = External synchronization disabled

   Bit 2 -  lace  (interlace enable)
      1 = interlaced mode enabled
      0 = non-interlaced mode enabled

   Bit 3 -  lpen  (light pen enable)

   Bits 4-7 not used (make 0)

   Bit 8 - GAUD (genlock audio enable)
      1 = Genlock audio enabled
      0 = Genlock audio disabled
      (This bit also appears on Denise pin ZD during blanking period)

   Bit 9 -  color_on  (color enable)
      1 = composite video color-burst enabled
      0 = composite video color-burst disabled

   Bit 10 -  dblpf  (double-playfield enable)
      1 = dual playfields enabled
      0 = single playfield enabled

   Bit 11 -  homod  (hold-and-modify enable)
      1 = hold-and-modify enabled
      0 = hold-and-modify disabled; extra-half brite ( ehb ) enabled
          if  dblpf =0 and  bpux =6

   Bits 14, 13, 12 -  bpu2, bpu1, bpu0 
      Number of bitplanes used.

      000 = only a background color
      001 = 1 bitplane, PLANE 1
      010 = 2 bitplanes, PLANES 1 and 2
      011 = 3 bitplanes, PLANES 1 - 3
      100 = 4 bitplanes, PLANES 1 - 4
      101 = 5 bitplanes, PLANES 1 - 5
      110 = 6 bitplanes, PLANES 1 - 6
      111 not used

   Bit 15 -  hires  (high resolution enable)
      1 = high resolution mode
      0 = low resolution mode


 bplcon1  - bitplane control

   Bits 3-0 - PF1H(3-0)  Playfield 1 delay

   Bits 7-4 - PF2H(3-0)  Playfield 2 delay

   Bits 15-8 not used


 bplcon2  - bitplane control

   Bit 6 - PF2PRI
      1 = Playfield 2 has priority
      0 = Playfield 1 has priority

   Bits 0-5  Playfield sprite priority

   Bits 7-15  not used


 ddfstrt  - data-fetch start
   (Beginning position for data fetch)

   Bits 15-8 - not used

   Bits 7-2 - pixel position H8-H3 (bit H3 only respected in Hires Mode.)

   Bits 1-0 - not used


 ddfstop  - data-fetch stop
   (Ending position for data fetch)

   Bits 15-8 - not used

   Bits 7-2 - pixel position H8-H3 (bit H3 only respected in Hires Mode.)

   Bits 1-0 - not used


 bplxpth  - bitplane pointer
   (Bitplane pointer high word, where x is the bitplane number)


 bplxptl  - bitplane pointer
   (Bitplane pointer low word, where x is the bitplane number)


 diwstrt  - display window start
   (Starting vertical and horizontal coordinates)

   Bits 15-8 - VSTART (V7-V0)

   Bits 7-0 - HSTART (H7-H0)


 diwstop  - display window stop
   (Ending vertical and horizontal coordinates)

   Bits 15-8 - VSTOP (V7-V0)

   Bits 7-0 - HSTOP (H7-H0)

 bpl1mod  - bitplane modulo
   (Odd-numbered bitplanes, playfield 1)


 bpl2mod  - bitplane modulo
   (Even-numbered bitplanes, playfield 2)