560,561



        TXT = PEEK(660) + PEEK(66l) * 256
     40  PRINT DLIST$;" "; DLIST,SAVMSC$;"
        ";SAV
     50  PRINT TXT$;" "; TEXT
     60  INPUT A: GRAPHICS A: GOTO 20

     Since an LMS is simply a map mode (graphics) or character
     mode (text) instruction with BIT six set, you can make any or all of
     these instructions into LMS instructions quite easily, pointing
     each line to a different RAM area if necessary. This is discussed
     in De Re Atari on implementing horizontal scrolling.

     DL's can be used to help generate some of the ANTIC screen
     modes that aren't supported by BASIC, such as 7.5 (ANTIC
     mode E) or ANTIC mode three, the lowercase with descenders
     mode (very interesting; ten scan lines in height which allow true
     descenders on lowercase letters).

     If you create your own custom DL, you POKE its address here.
     Hitting BESET or changing GRAPHICS modes will restore the
     OS DL address, however. The display list instruction is loaded
     into a special register called the Display Instruction Register (IR).
     which processes the three DL instructions (blank, jump, or
     display). It cannot be accessed directly by the programmer in
     either BASIC or machine language. A DL cannot cross a 1K
     boundary unless a jump instruction is used.

     There are only four display list instructions: blank line (uses BAK
     color), map mode, text mode, and jump. Text (character mode)
     instructions and map mode (graphics) instructions range from
     two to 15 ($2 to $F) and are the same as the ANTIC GRAPHICS
     modes. A DL instruction byte uses the following conventions
     (functions are enabled when the bit is set to one):

     Bit   Decimal   Function
     7       128     Display List Interrupt when set (enabled
                     equals one)
     6        64     Load Memory Scan. Next two bytes are the
                     LSB/MSB of the data to load.
     5        32     Enable vertical fine scrolling.
     4        16     Enable horizontal fine scrolling.
     3-0     8-1     Mode
                     0  0  1  0  Character
                       to        Modes
                     0  1  1  1
                     . . . . . . .
                     1  0  0  0  Map
                       to        Modes
                     1  1  1  1