Atari XL - Page 142

132 The Atari XL Handbook
GRAPHICS command will allow the entire
display to be used for multicolour characters.
Mode 12 allows 40 columns by 24 rows of
characters - the same as mode o. Mode 13 allows 40
columns by 12 rows of multicolour characters, the
characters being twice as tall as those in mode 12.
Type in the following program to see some
multicolour characters.
10 GRAPHICS 12
20 PRINTit6i"MULTICOLOUR
CHARACTERS"
You may just be able to discern the message - it is
certainly multicoloured, but hardly legible!
This is because in mode 12 (and mode 13) the
information defining a character is interpreted
differently by the computer. A multicolour
character is still defined by eight bytes of character
memory, but each pixel comprising the character is
represented by two bits rather than one. This
means that multicolour characters are only four
pixels wide, but the pixels are double the normal
width so characters are the same size as in other
modes. The extra information available in two bits
is used to select the colour of that pixel.
The multicolour characters can be designed on a
similar eight by eight grid to that used for standard
characters, as shown opposi te.
There are four possible combinations of two bits,
00, 01, 10 and 11, and each of these represents a
different colour or rather specifies a different
colour register.
Press the RESET key (to return the colour registers
to their default values) and type in the following