For more flexibility in designing your background display, you can specify
two playfields instead of one.  In dual-playfield mode, one playfield is
displayed directly in front of the other.  For example, a computer game
display might have some action going on in one playfield in the
background, while the other playfield is showing a control panel in the
foreground. You can then change either the foreground or the background
without having to redesign the entire display. You can also move the two
playfields independently.

A dual-playfield display is similar to a single-playfield display,
differing only in these aspects:

   *  Each playfield in a dual display is formed from one, two or three
      bitplanes.

   *  The colors in each playfield (up to seven plus transparent) are
      taken from different sets of color registers.

   *  You must set a bit to activate dual-playfield mode.

Figure 3-12 shows a dual-playfield display.

     figure 3-12: a dual-playfield display 

In Figure 3-12, one of the colors in each playfield is "transparent"
(color 0 in playfield 1 and color 8 in playfield 2). You can use
transparency to allow selected features of the background playfield to
show through.

In dual-playfield mode, each playfield is formed from up to three
bitplanes.  Color registers 0 through 7 are assigned to playfield 1,
depending upon how many bitplanes you use.  Color registers 8 through 15
are assigned to playfield 2.

 bitplane assignment in dual-playfield mode 
 color registers in dual-playfield mode 
 dual-playfield priority and control 
 activating dual-playfield mode 
 dual playfield summary