Atari XL - Page 133

Characters
123
obtained. For example, in the bottom row, the sum
IS:
64 + 2 = 66
and for the top row where no bits are set the answer
is O.
In this way, you can obtain eight numbers which
define your character.
All that remains is to choose the character you
wish to reprogram, find the start address of the
data defining it, using the formula on page 117,
and replace the data with your own.
If you add the following lines to the program on
page 120, the @ symbol will be turned into an
invader.
200 CHAR = 32*8+RAMSET
210 FOR Z=O TO 7
220 READ D
230 POKE CHAR+Z,D
240 NEXT Z
250 DATA 0,153,189,219,126,36,60,
66
From now on, until you press RESET, enter
another graphics mode or redefine it, the @ symbol
will appear as an invader.
While on the subject of invaders, it is quite easy to
achieve their limited form of animation - by
reprogramming several character sets, each
containing a slightly different version of the
character. To animate, simply move the character
set data pointer (location 756) to each set in turn.