Commodore Plus 4 - Page 216

204 Programming Graphics
20 The entire 128 character set is copied (8*128 = 1024).
30 The upper/lower case characters are copied from ROM to RAM at 8192
($2000).
40 Get the next byte.
50 The BASIC function PEEK is restored to normal operation.
60 The graphic chip character base address is set to 8192 ($2000).
70 The graphic chip reads character patterns from RAM.
80 The S§ and SHIFT key combination does not switch the charaacter set
base address.
90 A new custom character is inserted into the first character (@) position.
100 A message including the new character is printed to the screen.
110 A prompt instructs the user of the program.
120 The program waits for keyboard input.
130 The graphic chip character base address is restored to 53248 ($D000).
140 The graphic chip reads character patterns from the character ROM.
150 The CS and SHIFT key combination is reenabled.
160 Program execution ends.
170 The data for the custom character (a degree symbol).
Multicolor Characters One of the major reasons for creating a custom charac
ter set is to use more than a single foreground color and the background color in a
character cell. In multicolor text mode, a pair of bits determine which of four
colors a pair of pixels will be. The character pattern is organized in a parallel
fashion with a high-resolution character, except that 2 bits together determine the
color of the corresponding pair of pixels on the screen. Each byte in the character
pattern determines the appearance of 8 pixels on the screen. The first 2 bits are the
first 2 pixels, the second 2 the next 2, and so on.
The bit patterns are assigned as follows:
Bit Pair Color Source
00 background 0 (65301)
01 background 1(65302)
10 background 2 (65303)
11 foreground