APPENDIX EIGHT ____________________________________________________________



Display Lists

A display list is a short program for the ANTIC chip, telling it how to
display data on the screen. This program includes such instructions as
how many blank lines to place on the screen for top boundaries, where
the screen display data is stored, what mode the line(s) to be displayed
are in, whether or not there is an interrupt to execute and where to find
the display list itself.

There are nine pre-programmed display lists (ten with the GTIA) you
use in BASIC, one for each GRAPHICS mode. You can examine the
display lists for each mode by running the program at location 560.
You can change these lists to suit your own needs without much effort.
It is quite easy to design and implement your own display list once you
know where it's located and what the proper instructions are.

Certain techniques, such as horizontal and vertical fine scrolling,
require that you modify the display list in order to properly display
your screen data. Sometimes you want to be able to display data in
more than one mode or mix graphics and text in the same screen.
These are all done by modifying the display list.

The smallest display list is for GRAPHICS 2, so I'll use it as an
example. It consists of a mere twenty odd bytes, but the format is the
same for every list; it's just the instructions that change. Use the
program listed in the Memory Map to examine the list or use a simple
two-liner such as:

10   GRAPHICS 2: P = PEEK(560) + PEEK
   (561) * 256
20   FOR N = 0 TO 23: PRINT PEEK(P +
   N);"	";: NEXT N

When you RUN this example, you should get this:

112 112 112 71 112 158 7 7 7 7 7 7 7 7 7 66
  96 159 2 2 2 65 88 158

Or something similar depending on your available memory. If you
change the GR.2 to GR.2 + 16, you will get:

112 112 112 71 112 158 7 7 7 7 7 7 7 7 7 7 7
  65 92 158

The display list instruction set is discussed at location 560, but here's a
chart to summarize it:

 Instruction   BASIC   Scan   Pixels  Bytes  Comments
Decimal   Hex   mode   lines   line   line
                                             Blank instructions
  0        0     --       1     --     --    1 blank line
 16       10     --       2     --     --    2 blank lines
 32       20     --       3     --     --    3 blank lines