87



     POKEing DINDEX with a number from zero to 11. POKE with
     seven after you have entered GRAPHICS mode eight, and it will
     give you a split screen with mode seven on top and mode eight
     below. However, in order to use both halves of the screen, you
     will have to modify location 89 (below) to point to the area of the
     screen you wish to DRAW in. (See Your Atan 400/800, pp. 280 -
     283.)
     Watch for the cursor out-of-range errors (number 141) when
     changing GRAPHICS modes in this manner and either PRINTing
     or DRAWing to the new mode screen. POKE 87 with the BASIC
     mode number, not the ANTIC mode number.
     Did you know you can use PLOT and DRAWTO in GR.0? Try
     this:

     10   GR.0 
     20   PLOT 0,0: DRAWTO 10,10: DRAWTO 0
        ,10
     30   DRAWTO 39,0: DRAWTO 20,23: DRAWT
        O 0,20
     40   GOTO 40

     You can also set the text window for PRINT and PLOT modes by
     POKEing 87 with the graphics mode for the window. Then you
     must POKE the address of the top left corner of the text window
     into 88 and 89 ($58, $59). The screen mode of the text window is
     stored at location 659 ($293).

     You may have already discovered that you cannot call up the
     GTIA modes from a direct command. Like the + 16 GRAPHICS
     modes, they can only be called up during a program, and the
     screen display will be reset to GR.0 on the first INPUT or PRINT
     (not PRINT#6) statement executed in these modes.

     Since this location only takes BASIC modes, you can't POKE it
     with the other ANTIC modes such as "E", the famous "seven-and-
     a-half" mode which offers higher resolution than seven and a four
     color display (used in Datasoft's Micropainter program). If you're
     not drawing to the screen, simply using it for display purposes,
     you can always go into the Display List and change the
     instructions there. But if you try to draw to the screen, you risk an
     out-of-bounds error (error number 141).

     See Creative Computing, March 1982, for an excellent look at
     mode 7.5. The short subroutine below can be used to change the
     Display List to GR.7.5:

     1000  GRAPHICS 8+16: DLIST = PEEK(560)
          ) + PEEK(561) * 256:POKE DLIST +
           3,78