Cirrus Logic EP93xx - Manual (Page 186)

7-4 DS785UM1
Copyright 2007 Cirrus Logic
Raster Engine With Analog/LCD Integrated Timing and Interface
EP93xx User’s Guide
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to one pixel combination blinking. For 16 bpp and 24 bpp modes, the LUT blink circuitry is
usually bypassed and the blink functions are logic transformations of the pixel data. In
addition to logical AND/OR/XOR LUT address translations, the circuitry will support logical
blink to background, blink dim, blink bright, and blink to reverse.
7.3.2 Color Look-Up Tables
The raster engine block contains dual color pixel LUTs (Look-Up-Tables). Each LUT will allow
the engine to output 256 different pixel combinations of 24-bit pixels in lower color depth
modes.
7.3.3 Grayscale/Color Generation for Monochrome/Passive Low Color
Displays
The video pipeline includes circuitry that can be configured to provide grayscale or color
generation for generating grayscales on monochrome displays or adding color depth on low
color LCD displays, respectively. For monochrome displays, the circuitry supports up to 8
grayscale shades including on and off. For low color LCD displays, the circuitry supports up
to 512 colors. The circuitry does this by rapidly turning on and off (dithering) pixels based on
frame count, screen location, and pixel value. For grayscale displays, the pixel gray
appearance is determined by 3 bits of the pixel data. For color depth expansion on LCD
displays, the pixel color appearance is determined by 3 bits each from the red, green, and
blue portions of the pixel data.
7.3.4 Frame Buffer Organization
The Raster Engine is designed to support video information as DIB (Device Independent
Bitmap) format stored in a packed pixel architecture. However, the engine does not require
that video information be stored in a packed line architecture. The circuitry allows a different
memory organization between video scan out and graphic image memory. Therefore,
memory gaps can exist between lines. This means that the graphics memory may be
organized wider than the video frame. This type of feature could be used for left and right
panning of the displayed information. The video frame buffer can be located in main memory,
or in a dedicated video frame area. The beginning of video lines can be located on any word
boundary. This architecture allows efficient use of memory regardless of the active video line
length. Video screen start registers determine the upper left corner of the video screen. Video
word addressing in screen memory is from left to right and then from top to bottom. Four-bit
pixels packed within video words are organized in DIB format with the left most pixel in the