Functional Description
1391
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
LCD Controller
20.3.7 Palette
As explained in
, the pixel data is an index of palette entry (when palette is used). The
number of colors supported is given by 2
number of BPP
. However, due to a limitation of the grayscaler and
serializer block, fewer grayscales or colors may be supported.
The PALMODE field in the LCD Raster Control (LCDRASTRCTL) register affects the palette loading:
•
If PALMODE is 0x0 (palette-plus-data mode) or 0x1 (palette-only mode), the palette is loaded by the
DMA engine at the very beginning, which is followed by the loading of pixel data.
•
If PALMODE is 0x2 (data-only mode), the palette is not loaded. Instead, the DMA engine immediately
loads the pixel data.
20.3.8 Grayscaler and Serializer – Passive (STN) Mode
Once a palette entry is selected from the look-up palette by the pixel data, its content is sent to the
grayscaler/ serializer. If it is monochrome data, it is encoded as 4 bits. If it is color data, it is encoded as 4
bits (Red), 4 bits (Green), and 4 bits (Blue). These 4-bit values are used to select one of the 16 intensity
levels, as shown in
. A patented algorithm is used during this processing to provide an
optimized intensity value that matches the eye's visual perception of color/gray gradations.
20.3.9 Grayscaler and Serializer – Active (TFT) Mode
The grayscaler and serializer is bypassed in this mode.
20.3.10 Color and Grayscale Intensities and Modulation Rates
lists the intensities and modulation rates for varying dither values.
Table 20-4. Intensities and Modulation Rates
Dither Value (4-Bit
Value from Palette)
Intensity (0% is
White)
Modulation Rate
(Ratio of ON to ON +
OFF Pixels)
0x0
0.0%
0
0x1
14.3%
1 / 7
0x2
20.0%
1 / 5
0x3
25%
1 / 4
0x4
33.3%
3 / 9
0x5
40.0%
2 / 5
0x6
44.4%
4 / 9
0x7
50.0%
1 / 2
0x8
55.6%
5 / 9
0x9
60.0%
3 / 5
0xA
66.6%
6 / 9
0xB
75%
3 / 4
0xC
80.0%
4 / 5
0xD
85.7%
6 / 7
0xE
93.3%
14 / 15
0xF
100.0%
1
20.3.11 Summary of Color Depth
summarizes the color depths depending on the number of BPP.