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)