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S3C2440A RISC MICROPROCESSOR LCD CONTROLLER
15-5
Table 15-1. Relation between VCLK and CLKVAL (STN, HCLK=60MHz)
CLKVAL 60MHz/X VCLK
2 60 MHz/4 15.0 MHz
3 60 MHz/6 10.0 MHz
: : :
1023 60 MHz/2046 29.3 kHz
VIDEO OPERATION
The S3C2440A LCD controller supports 8-bit color mode (256 color mode), 12-bit color mode (4096 color mode),
4 level gray scale mode, 16 level gray scale mode as well as the monochrome mode. For the gray or color mode, it
is required to implement the shades of gray level or color according to time-based dithering algorithm and Frame
Rate Control (FRC) method. The selection can be made following a programmable lockup table, which will be
explained later. The monochrome mode bypasses these modules (FRC and lookup table) and basically serializes
the data in FIFOH (and FIFOL if a dual scan display type is used) into 4-bit (or 8-bit if a 4-bit dual scan or 8-bit
single scan display type is used) streams by shifting the video data to the LCD driver.
The following sections describe the operation on the gray and color mode in terms of the lookup table and FRC.
Lookup Table
The S3C2440A can support the lookup table for various selection of color or gray level mapping, ensuring flexible
operation for users. The lookup table is the palette which allows the selection on the level of color or gray
(Selection on 4-gray levels among 16 gray levels in case of 4 gray mode, selection on 8 red levels among 16
levels, 8 green levels among 16 levels and 4 blue levels among 16 levels in case of 256 color mode). In other
words, users can select 4 gray levels among 16 gray levels by using the lookup table in the 4 gray level mode. The
gray levels cannot be selected in the 16 gray level mode; all 16 gray levels must be chosen among the possible 16
gray levels. In case of 256 color mode, 3 bits are allocated for red, 3 bits for green and 2 bits for blue. The 256
colors mean that the colors are formed from the combination of 8 red, 8 green and 4 blue levels (8x8x4 = 256). In
the color mode, the lookup table can be used for suitable selections. Eight red levels can be selected among 16
possible red levels, 8 green levels among 16 green levels, and 4 blue levels among 16 blue levels. In case of 4096
color mode, there is no selection as in the 256 color mode.
Gray Mode Operation
The S3C2440A LCD controller supports two gray modes: 2-bit per pixel gray (4 level gray scale) and 4-bit per pixel
gray (16 level gray scale). The 2-bit per pixel gray mode uses a lookup table (BLUELUT), which allows selection on
4 gray levels among 16 possible gray levels. The 2-bit per pixel gray lookup table uses the BULEVAL[15:0] in Blue
Lookup Table (BLUELUT) register as same as blue lookup table in color mode. The gray level 0 will be denoted by
BLUEVAL[3:0] value. If BLUEVAL[3:0] is 9, level 0 will be represented by gray level 9 among 16 gray levels. If
BLUEVAL[3:0] is 15, level 0 will be represented by gray level 15 among 16 gray levels, and so on. Following the
same method as above, level 1 will also be denoted by BLUEVAL[7:4], the level 2 by BLUEVAL[11:8], and the level
3 by BLUEVAL[15:12]. These four groups among BLUEVAL[15:0] will represent level 0, level 1, level 2, and level
3. In 16 gray levels, there is no selection as in the 16 gray levels.