ADE3700SX datasheet(64/89 Pages) STMICROELECTRONICS

64 / 89 page

On-Screen Display (OSD)

ADE3700

64/89

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.

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