88,89



          Z = Z + 1
     30  GOTO 10

     You will notice that you get the Atari internal character code, not
     the ATASCII code. See also locations 560, 561 ($230, $231) and
     57344 ($E000).

     How do you find the entire screen RAM? First, look at the chart
     below and find your GRAPHICS mode. Then you multiply the
     number of rows-per-screen type by the number of bytes-per-line.
     This will tell you how many bytes each screen uses. Add this
     value, minus one, to the address specified by SAVMSC.
     However, if you subtract MEMTOP (locations 741, 742; $2E5,
     $2E6) from RAMTOP (106; $6A * 256 for the number of bytes),
     you will see that there is more memory reserved than just the
     screen area. The extra is taken up by the display list or the text
     window, or is simply not used (see the second chart below).

     Mode          0    1    2    3    4    5    6    7    8 9-12

     Rows
     Full         24   24   12   24   48   48   96   96  192  192
     Split        --   20   10   20   40   40   80   80  160  --

     Bytes per
     Line         40   20   20   10   10   20   20   40   40   40

     Columns
     per Line     40   20   20   40   80   80  160  160  320   80

     Memory (1)  993  513  261  273  537 1017 2025 3945 7900 7900

     Memory (2)
     Full        992  672  420  432  696 1176 2184 4200 8138 8138
     Split        --  674  424  434  694 1174 2174 4190 8112  --

     (1) According to the Atari BASIC Reference Manual, p.45; OS
     User's Manual, p.172, and Your Atari 400/800, p.360.

     (2) According to Your Atari 400/800, p.274, and Atari Microsoft
     Basic Manual, p.69. This is also the value you get when you
     subtract MEMTOP from RAMTOP (see above).

     For example, to POKE the entire screen RAM in GR.4, you
     would find the start address of the screen (PEEK(88) + PEEK(89)
     * 256), then use a FOR-NEXT loop to POKE all the locations
     specified above:

     10   GRAPHICS 4: SCRN = PEEK(88) + PE
        EK(89) * 256
     20   FOR LOOP = SCRN to SCRN + 479: R
        EM 48 ROWS * 10 BYTES - 1
     30   POKE LOOP,35: NEXT LOOP