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Barracuda PDA Maintenance
SA-1110 Processor LCD controller:
The SA-1110's LCD controller has three types of displays:
Passive Color Mode..... Supports a total of 375 possible colors, displaying any of 256 colors for each frame.
Active Color Mode......Supports up to 65535 colors (16-bit).
Passive Monochrome Mode ... Supports 15 gray-scale levels.
Display size up to 1024 x 1024 pixels are supported. However, the size of encoded pixel data within the frame
buffer limits the maximum size screen the LCD can drive due to memory bus bandwidth.
The LCD controller also supports single- or dual displays. Encoded pixel data is stored in external memorv in a
frame buffer in 4-, 8-, 12-, or 16-bit increments and is loaded into a 5-entry FIFO (32 bits per entry ) on a demand
basis using the LCD's own dedicated dual-channel DMA controller. One channel is used for single-panel displays
and two are used for dual-panel displays.
Frame buffer data contains encoded pixel values that are used by the LCD controller as pointers to index into a
256-entry x 12-bit wide palette. Monochrome palette entries are 4 bits wide; color palette entries are 12 bits wide.
Encoded pixel data from the frame buffer. which is 4 bits wide, address the top 16 locations of the palette; 8-bit
pixel data accesses any the 256 entries within the palette. When passive color 12-bit pixel mode is enable, the
color pixel values bypass the palette and are fed directly to the LCD's dither logic. When active color 16-bit pixel
mode is enabled, the pixel value not only bypasses the palette, but also bypasses the dither logic and is sent
directly to the LCD's data pins.
Once the 4- or 8-bit encoded pixel value to select a palette entry, the value programmed within the entry is
transferred to the dither logic, which uses a patented space- and time- based dithering algorithm to produce
the pixel data that is output to the screen. Dithering causes individual pixels to be turned off on each frame at
varying rates to produce the 15 levels of gray for monochrome screen and 15 levels each for the red, green,
and blue pixel components for color screens, providing a total of 3375 colors (256 colors are available on each
frame). The data output from the dither logic is placed in a 19-entry pin data FIFO before it is placed out on the
LCD's pins and driven to the display using pixel clock.
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