Figure 6-13 shows the basic building blocks for a single bit of a 16-bit
wide operation of the blitter.  It does not cover the line-drawing
hardware.

     figure 6-13: blitter block diagram 

*  The upper left corner shows how the first-- and last-- word  masks  are
   applied to the incoming A-source data.  When the blit shrinks to one
   word wide, both  masks  are applied.

*  The shifter (upper right and center left) drawing illustrates how 16
   bits of data is taken from a specified position within a 32-bit
   register, based on the A  shift  or b  shift  values shown in  bltcon0 
   and  bltcon1 .

*  The  minterm  generator (center right) illustrates how the  minterm 
   select bits either allow or inhibit the use of a specific  minterm .

*  The drawing shows how the fill operation works on the data generated
   by the  minterm  combinations.  fill operations can be performed
   simultaneously with other complex logic operations.

*  At the bottom, the drawing shows that data generated for the
   destination can be prevented from being written to a destination by
   using one of the blitter control bits.

*  Not shown on this diagram is the logic for zero detection, which
   looks at every bit generated for the destination.  If there are any
   1-bits generated, this logic indicates that the area of the blit
   contained at least one 1-bit (zero detect is false.)