LCD Controller Operation
11-9
LCD Controller
11.3 LCD Controller Operation
The LCD controller supports a variety of user-programmable options, includ-
ing display type and size, frame buffer pixel size, and output data width.
Although all programmable combinations are possible, the selection of
displays available within the market dictate which combinations of these
programmable options are practical. In addition, the type of external memory
system implemented by the user limits the bandwidth of the LCD DMA control-
ler, which in turn limits the size and type of screen that can be controlled.
The following sections describe individual functional blocks within the LCD
controller, the frame buffer and palette memory organization, and the LCD
DMA controller. The sections are arranged in order of data flow, starting with
the off-chip frame buffer and ending with the pins that interface to the LCD
display.
11.3.1 Frame Buffer
The frame buffer is an area within on-chip SRAM or off-chip memory that is
used to supply enough encoded pixel values to fill the entire screen one time.
The first 32 bytes of the buffer (for 2-, 4-, 12-, and 16-bit mode operation, 512
bytes for 8 BPP mode of operation) are used to store the look-up palette data
for each frame. Not all of the 16 entries of the palette are used in 2 BPP mode.
However, all 16 palette entries must be present. The palette is not used for
12 or 16 bits-per-pixel encoding. The 32 bytes at the top of the frame buffer,
however, must be zero-filled even though the data is not used. This is to
provide the bits-per-pixel to the LCD controller.
Each time a new frame is fetched from the frame buffer, the LCD controller
palette is first loaded with data contained within the palette buffer (this is the
default setting). Figure 11–3 and Figure 11–4 show the palette entry organiza-
tion. You can configure the LCD palette loading by setting the LCD control
register bits 21 - 20.