HD66421 Datasheet, PDF (20/46 Pages) Hitachi Semiconductor – (RAM-Provided 160 Channel 4-Level Grey Scale Driver for Dot Matrix Graphics LCD)

Preliminary
Configuration of Display Data Bit
Packed Pixel Method
For grey scale display and super reflective
colour display, multiple bits are needed for one
pixel. In the HD66421, two bits are assigned to
one pixel, enabling a four-level grey scale
display and four colour display.
One address, eight bits, specifies four pixels,
and pixel bits 0 and 1 for gray scale are
managed as consecutive bits in one byte.
Rev. 1.1E '99.02.10
HD66421
When grey scale display data is manipulated in
bit units, one memory access is sufficient,
which enables smooth high-speed data
rewriting.
The bit data to input to pin DB7, DB5, DB3
and DB1 become MSB and the bit data to
input via pin DB6, DB4, DB2 and DB0 are
LSB.
LCD display state
Grey scale/colour palette
FRC control circuit
00011011
Bit 7 6 5 4 3 2 1 0
00001010
76543210
4 pixels/address
Address: n
Address: n + 1
Figure 15 Packed Pixel Method
Physical memory
Gray scale/Colour palette
The HD66421 uses PWM, Pulse Width
Modulation, technique for gray scale display. A
period of one line is divided into thirty-one or
four and HD66421 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 HD66421 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 DB6, 4, 2, 0 Register Name
0
0
Grayscale Palette 1
0
1
Grayscale Palette 2
1
0
Grayscale Palette 3
1
1
Grayscale Palette 4
Default Value
00000
01011
10111
11111
20