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Color Liquid Crystal Display Controller
13.2 CLCDC Theory of Operation
The basic function of the CLCDC is to retrieve image data from system memory (the frame
buffer), format the data for the LCD panel, and write it to the panel. The CLCDC also cre-
ates the control signals that cause the panel to display the formatted data.
A set of numbers representing the color or gray scale of each pixel the CLCDC displays is
stored in a region of static memory called a frame buffer. The CLCDC uses its DMA con-
troller to fetch data from the frame buffer into its FIFO (or FIFOs for dual-panel interfaces)
when the amount of pixel data falls below the FIFO watermark.
Data moves from the frame buffer into the FIFO via the AHB. The frame buffer can reside
on either the external memory bus or on the internal SRAM. Because the TCM SRAM does
not reside on the AHB, the frame buffer cannot be placed in TCM SRAM.
13.2.1 LCD DMA FIFOs
The CLCDC has an upper LCD DMA FIFO and a lower LCD DMA FIFO. These FIFOs can
be independently controlled to cover single- and dual-panel LCDs. Each FIFO is 16 words
deep by 32 bits wide. In single-panel modes the LCD DMA FIFOs are made to appear as
a single FIFO of twice the size.
The water level marks within each FIFO are set so that each FIFO requests data when the
level of data in a FIFO falls below the programmed watermark (either four or eight locations,
as specified by bit [16] of the LCD Panel Pixel Parameter Register. An interrupt signal is
asserted, if enabled, if either of the two LCD DMA FIFOs is read when they are empty.
13.2.2 Pixel Serializer
The pixel serializer reads the 32-bit-wide LCD data from the output port of the LCD DMA
FIFO and extracts 12, 8, 4, 2, or 1 bits per pixel (bpp) data, depending on the operating
mode. In Dual Panel Mode, data alternately is read from the upper and lower LCD DMA
FIFOs. Depending on the operating mode, the extracted data is either used to point to a
color/grayscale value in the palette RAM or directly applied to an LCD panel input.
13-4
LH75400/01/10/11 (Preliminary) User's Guide
7/15/03
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