703



703            2BF            BOTSCR
     Flag for the number of text rows available for printing. 24 ($18) is
     normal for text mode GR.0; four for the text window, zero for all
     graphics modes. In all GRAPHICS modes except zero, if there is
     no text window then 703 will also read zero. The large-text
     displays in GR.1 and GR.2 are treated as graphics displays for
     this purpose. The display handler specifically checks for split-
     screen mode by looking for the variable 24 or four here. If it finds
     24 here, it assumes there is no text window; if not, it looks for the
     variable four.

     You can add a text window to GR.0 by POKEing here with four.
     The top portion (20 lines) of the screen will not scroll with the
     bottom. To write to the top part of the screen you will have to use
     the PRINT#6 statement as with modes one and two. One possible
     application of this would be to keep a fixed menu at the top of the
     screen while scrolling the bottom part, as done with the DOS
     menu.

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Locations 704 to 712 ($2C0 to $2C8) are the color registers for players,
missiles, and playfields. These are the RAM shadow registers for
locations 53266 to 53274 ($D012 to $D01A). For the latter, you can use
the SETCOLOR command from BASIC. For all registers you can
POKE the desired color into the location by using this formula:

COLOR = HUE * 16 + LUMINANCE

It is possible to get more colors in GR.8 than the one (and a half) that
Atari says is possible by using a technique called artifacting. There is a
small example of artifacting shown at location 710 ($2C6). See De Re
Atari, Your Atari 400/800, Creative Computing, June 1981, and
COMPUTE!, May 1982.

Here are the 16 colors the Atari produces, along with their POKE
values for the color registers. The POKE values assume a luminance of
zero. Add the luminance value to the numbers to brighten the color.
The color registers ignore BIT 0; that's why there are no "odd" values
for luminance, just even values.

Color             Value         Color             Value
Black           0,      0	Medium blue     8,    128
Rust            1,     16       Dark blue       9,    144
Red-orange      2,     32       Blue-grey      10,    160
Dark orange     3,     48       Olive green    11,    176
Red             4,     64       Medium green   12,    192
Dk lavender     5,     80       Dark green     13,    208
Cobalt blue     6,     96       Orange-green   14,    224
Ultramarine     7,    112       Orange         15,    240