Atari XL

Characters
115
85 FOR DELAY=O TO 30:NEXT DELAY
90 NEXT LUM
100 GOTO 70
110 DATA 104,97,112,112,121,32,
32,118
120 DATA 97,108,101,110,116,105,
110,101
The screen full of hearts occurs because the
character corresponding to space in the first half of
the character set is a heart, so everywhere which
would normally be blank contains a heart. The
colour of the hearts is set in line 25, and the second
half of the character set specified in line 30.
If you change line 30 to:
30 POKE 756,224
and run the program again, the first half of the
character set will be used but the resulting display
doesn't have the same romantic appeal!
CHARACTER DEFINITIONS
The shapes of all the displayable characters are
defined by numbers held in a special area of
memory. The XL allows you to create new symbols
by entering new definitions for the characters to
replace those held in memory. Each symbol in the
character set is defined by the contents of eight
memory locations, which correspond to a grid of
eight rows; each row consisting of eight dots which
may be set to the foreground or the background .
colour. (Each of these dots is called a pixel, which is
a
contraction of picture element. The display is
built up from 69120 of these pixels.) Each location
defines one row of the character, and each bit of the
number in the location represents one pixel. If the
bit is set to 1, the pixel is displayed in the