1061
SAM9G45 [DATASHEET]
6438K–ATARM–12-Feb-13
The lookup table can be accessed by the host in R/W mode to allow the host to program and check the values
stored in the palette. It is mapped in the LCD controller configuration memory map. The LUT is mapped as 16-bit
half-words aligned at word boundaries, only word write access is allowed (the 16 MSB of the bus are not used). For
The lookup table contains 256 16-bit wide entries. The 256 entries are chosen by the programmer from the 216
possible combinations.
In STN Monochrome, only the four most significant bits of the red value are used (16 gray shades). In STN Color,
only the four most significant bits of the blue, green and red value are used (4096 colors).
In TFT mode, all the bits in the blue, green and red values are used. The LCDD unused bits are tied to 0 when TFT
palletized configurations are used (LCDD[18:16], LCDD[9:8], LCDD[2:0]).
45.6.2.6
Dithering
The dithering block is used to generate the shades of gray or color when the LCD Controller is used with an STN
LCD Module. It uses a time-based dithering algorithm and Frame Rate Control method.
The Frame Rate Control varies the duty cycle for which a given pixel is turned on, giving the display an appearance
of multiple shades. In order to reduce the flicker noise caused by turning on and off adjacent pixels at the same
time, a time-based dithering algorithm is used to vary the pattern of adjacent pixels every frame. This algorithm is
expressed in terms of Dithering Pattern registers (DP_i) and considers not only the pixel gray level number, but
also its horizontal coordinate.
Table 45-11 shows the correspondences between the gray levels and the duty cycle.
STN Mono
4
Non-palletized
STN Color
1, 2, 4, 8
Palletized
STN Color
16
Non-palletized
Table 45-10. Lookup Table Structure in the Memory
Address
Data Output [15:0]
00
Red_value_0[4:0]
Green_value_0[5:0]
Blue_value_0[4:0]
01
Red_value_1[4:0]
Green_value_1[5:0]
Blue_value_1[4:0]
...
FE
Red_value_254[4:0]
Green_value_254[5:0]
Blue_value_254[4:0]
FF
Red_value_255[4:0]
Green_value_255[5:0]
Blue_value_255[4:0]
Table 45-9.
Palette Configurations (Continued)
Configuration
Palette
DISTYPE
PIXELSIZE
Table 45-11. Dithering Duty Cycle
Gray Level
Duty Cycle
Pattern Register
15
1
-
14
6/7
DP6_7
13
4/5
DP4_5
12
3/4
DP3_4