
HD66841
27
Gray-Scale Palette
The HD66841 thins out LCD data on certain dots or lines of an LCD panel every frame, changing integral
voltages applied to liquid-crystal cells, to generate intermediate levels of luminosities. Consequently the
difference in depth between adjacent gray-scale shades may not be uniform in some cases since voltage-
transmittance characteristics vary with different panels. To allow for this, the HD66841 is designed to
generate 13 gray-scale levels and provide palette registers that assign desired levels to certain of the eight
CRT display colors.
The relationships between gray scales and corresponding effective applied voltages are shown in Figure 12
(a). Each gray scale is displayed according to the characteristics of its effective applied voltage and the
optical transmittance of the panel (Figure 12 (b)). Using the palette registers to select any 8 out of 13 levels
of applied voltages enables an optimal gray-scale display conforming to the characteristics of the LCD
panel. The palette registers can also be used to provide 4-level grayscale display and reverse display.
Table 12
Default Values of Palette Registers
CRT Display Data
G
0
0
0
0
1
1
1
1
Register No.
P1
P2
P3
P4
P5
P6
P7
P8
R
0
0
1
1
0
0
1
1
B
0
1
0
1
0
1
0
1
Register Name
Black palette
Blue palette
Red palette
Magenta palette
Green palette
Cyan palette
Yellow palette
White palette
Default Value
0
0
0
0
0
1
0
1
0
1
1
0
1
0
1
1
0
1
0
1
1
0
1
0
0
0
1
0
1
0
0
0
1
3
5
7
9
11
13
1
1
Gray-scale number
(a)
Transmittance
(b)
E
E
Figure 12 Relationships between Gray Scale, Transmittance, and Effective Applied Voltage