ade3700 STMicroelectronics, ade3700 Datasheet - Page 64

• Manufacturer Part Number: ade3700
• Description: Analog Lcd Display Engine For Xga And Sxga Resolutions
• Manufacturer: STMicroelectronics

On-Screen Display (OSD)
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effects. An alpha value of 255 makes the OSD opaque, while a value of 0 makes the OSD invisible,
with a linear ramp of transparency between these two endpoints. Separate registers control alpha
for foreground and background pixels.
A fade-in/fade-out feature ramps the alpha values every six frames, starting from their current value
and going up or down the sequence: 0, 16, 32, 64, 128, 192, 224, 240, 255.
Row 15 also contains definitions for the four display windows. These windows define regions on the
screen to which borders and shadows can be applied. (They are not analogous to windows in a GUI
display, in that they do not represent four independent data displays. There is only one character
map. The windows essentially define an area around which a border can be drawn or to which
attributes can be assigned.) Windows also determine which of the two color tables will be used for
the characters inside. Windows have a fixed precedence: Window 0 has the highest precedence
and Window 3 the lowest. When windows overlap, the precedence determines which borders will
be displayed and which color tables will be used in the overlapping area.
Monochrome and color fonts are affected differently by attribute bytes. Monochrome characters are
affected by shadows and borders, and have their color specified by the foreground/background
attributes. Color characters interpret the attribute byte differently than monochrome characters,
using it to define blinking and 90-degree rotations rather than blinking, foreground color, and
background color.
Color Tables
There are two color tables, each containing sixteen entries by three bytes each, giving a 24-bit RGB
value for each entry. Entry 0 is used for the shadow color for monochrome characters and borders.
Color-table selection is made on a window-by-window basis.
When writing the color table, the “row” value in the first header byte is interpreted as the color table
index, while the “column” value in the second header byte encoded to select the color table (0 or 1)
and the primary color (red, green, or blue). The data byte following the second header byte is
written to the selected (table, index, primary) location.
Font Data
Font data is sent to the OSD through burst transfers. The first header byte selects the transfer type
and provides three bits of the character index, while the second header byte selects transfer type
“C” and gives the remaining five bits of offset. The data bytes for the character follow, given from top
to bottom and left to right in the character cell.
A monochrome character is 27 bytes long, with two scan-lines occupying three bytes. A color
character is four times as long as a monochrome character (108 bytes), with each byte containing
two four-bit pixels. Both color and monochrome fonts are 12 pixels wide and 18 high.
Transfer Formats
The transfer format consists of two header bytes and a variable number of data bytes. The header
bytes determine the type of transfer (character, attribute, monochrome font, color font, or color
table). Addressing is by row and column in the case of character or attribute transfers, and by
character index in the case of font transfers.
When writing to the color table, the “column” field determines the color table and R/G/B selection.
ADE3700