The maximum size of a playfield display is determined by the maximum
number of lines and the maximum number of columns. Vertically, the
restrictions are simple. No data can be displayed in the
 vertical blanking  area. The following table shows the allowable vertical
display area.


                              NTSC                 PAL
                              ----                 ---

     Vertical Blank Start     0                    0
      Vertical Blank Stop     $15 (21)             $1D (29)


                              NTSC     NTSC        PAL      PAL
                              Normal   Interlaced  Normal   Interlaced
                              ------   ----------  ------   ----------
        Displayable lines
          of screen video     241      483         283      567
                                       =525-(21*2)          =625-(29*2)


        Table 3-13: Maximum Allowable Vertical Screen Video


Horizontally, the situation is similar. Strictly speaking, the hardware
sets a rightmost limit to  DDFSTOP  of ($D8) and a leftmost limit to
 DDFSTRT  of ($18). This gives a maximum of 25 words fetched in low
resolution mode. In high resolution mode the maximum here is 49 words,
because the rightmost limit remains ($D8) and only one word is fetched at
this limit. However, horizontal blanking actually limits the displayable
video to 368 low resolution pixels (23 words). These numbers are the same
both for NTSC and for PAL. In addition, it should be noted that using a
data-fetch start earlier than ($38) will disable some  sprites .


        Table 3-14: Maximum Allowable Horizontal Screen Video

                                   Lores            Hires
                                   -----            -----
         DDFSTRT  (standard)       $0038            $003C
         DDFSTOP  (standard)       $00D0            $00D4

         DDFSTRT  (hw limits)      $0018            $0018
         DDFSTOP  (hw limits)      $00D8            $00D8

         max words fetched         25               49
         max display pixels        368 (low res)


The limits on the display window starting and stopping positions described
in this section apply to the Amiga's original custom chip set. In the
Enhanced Chip Set (ECS), the limits for playfield display windows have
been changed.  For more information on  ECS and playfield display windows 
refer to Appendix C, Enhanced Chip Set.

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