HD66420 Datasheet, PDF (21/52 Pages) Hitachi Semiconductor – (RAM-Provided 160 Channel 4-Level Grey Scale Driver for Dot Matrix Graphics LCD)

HD66420
Gray scale/Colour palette
The HD66420 uses PWM, Pulse Width Modulation, technique for gray scale display. A period of one line
is divided into thirty-one or four and HD66420 outputs turn-on levels for one period and turn-off levels for
rest of these period. This technique changes gray scale on monochrome display and colour on super
reflective colour panel. The characteristics of these panel vary with different panel. To allow for this, the
HD66420 designed to generate 32-levels gray scale levels and provides palette registers that assign desired
levels to certain of the four colours, GRAY = 0, or generate dedicated 4-level grayscale , GRAY = 1. Using
the palette registers to select any 4 out of 32 levels of applied voltages enables an optimal grayscale/colour
display. Because of this grayscale technique using 32-levels gray scale needs higher clock rate. If 32-levels
gray scale is not needed, lower clock rate can be used. Table 3 shows default value of palette registers and
Table 4 and 5 show relationship between value of a palette register and grayscale level.
Table 3 Default Value of Palette Registers
DB7, 5, 3, 1
0
1
DB6, 4, 2, 0
0
1
0
1
Register Name
Grayscale Palette 1
Grayscale Palette 2
Grayscale Palette 3
Grayscale Palette 4
Default Value
0
0
0
0
0
0
1
0
1
1
1
0
1
1
1
1
1
1
1
1
21