Commodore Plus 4 - Page 236

224 Programming Graphics
high-resolution bit map, except that each pair of dots on the screen is controlled
by a pair of bits in memory. This cuts the resolution to 160 by 200 (32000 dots).
But the color flexibility is increased by the addition of two global colors.
Within each byte of the bit map, the high 2 bits determine the color of the leftmost
pair of dots on the screen. The 2 low bits determine the color of the rightmost pair
of dots on the screen. The colors are determined as follows:
Bit Pair Luminance Source Color Source
00 $FF15 $FF15
01 low nybble of luminance high nybble of color
10 high nybble of luminance low nybble of color
11 SFF16 $FF16
Summary of Memory Map Considerations
This section is organized by each type of graphics mode and details the use of
memory. It is intended for quick reference. The previous section explains the
actual operation of each mode.
High-Resolution Characters
$FF07 Bit 7 determines hardware reverse on and 128 characters (0), or
reverse off and 256 characters (1).
SFF12 Bit 2 determines RAM (0) or ROM (1).
$FF13 Bits 7-2 determine location of character set (bits 15-10).
$FF14 Bits 7-3 determine location of color/screen memory (bits 15-11).
$FF15 Background luminance and color.
$FF19 Border luminance and color.
Character color* luminance, and flashing are determined by color memory (nor
mally $0800-$0BE7). Characters displayed are determined by screen memory
(normally $0C00-$0FE7).
Extended Color Characters
$FF06 Set bit 6 for extended color mode.
$FF07 Bit 7 determines 128 characters (0), or 256 characters (1).