LM1247 National Semiconductor, LM1247 Datasheet - Page 19

• Manufacturer Part Number: LM1247
• Description: 150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs
• Manufacturer: National Semiconductor

OSD Generator Operation
ATTRIBUTE TABLES
Each character has an attribute value assigned to it in the
page RAM. The attribute value is 4 bits wide, making each
character entry in the page RAM 12 bits wide in total. The
attribute value acts as an address which points to one of 16
entries in either the two-color attribute table RAM or the
four-color attribute table RAM. The attribute word in the table
contains the coding information which defines which color is
represented by color 0 and color 1 in the two color attribute
table and color 0, color 1, color 2, color 3 in the four-color
attribute table. Each color is defined by a 9-bit value, with 3
bits assigned to each channel of RGB. A dynamic look-up
table defines each of the 16 different color “palettes”. As the
look-up table can be dynamically coded by the microcontrol-
ler over the I
assigned to any one of 2
maximum of 64 different colors to be used within one page
using the 4-color characters, with up to 4 different colors
within any one character and 32 different colors using the
2-color characters, with 2 different colors within any one
character.
TRANSPARENT DISABLE
In addition to the 9 lines of video data, a tenth data line is
generated by the transparent disable bit. When this line is
activated, the black color code will be translated as “trans-
parent” or invisible. This allows the video information from
the PC system to be visible on the screen when this is
present. Note that this feature is enabled on any black color
in of the first 8 attribute table entries.
ENHANCED FEATURES
In addition to the wide selection of colors for each character,
additional character features can be selected on a character
by character basis. There are 3 Enhanced Feature Regis-
ters, EF0, EF1 and EF2.
1. Button Boxes — The OSD generator examines the char-
acter string being displayed and if the “button box” at-
2
C compatible interface, each color can be
9
(i.e. 512) choices. This allows a
FIGURE 18. Displaying Each Character Individually
(Continued)
19
2. Heavy Button Boxes — When heavy button boxes are
3. Shadowing — Shadowing can be added to two-color
4. Bordering — A border can be added to the two-color
5. Blinking — If blinking is enabled as an attribute, all colors
tributes have been set in the Enhanced feature byte,
then a box creator selectively substitutes the character
pixels in either or both the top and left most pixel line or
column with a button box pixel. The shade of the button
box pixel depends upon whether a “depressed” or
“raised” box is required, and can be programmed
through the I
color (“highlight”) is defined by the value in the color
palette register, EF1 (0x8405 - 0x8406), which is nor-
mally set to white. The depressed pixel (“lowlight”) color
by the value in the color palette register, EF2 (0x8407 -
0x8408), which is normally set to gray. See Figure 19 for
detail and Figure 20 for the on-screen effect.
selected, the color palette value stored in register EF3
(0x8409 - 0x840A) is used for the depressed (“lowlight”)
pixel color instead of the value in register EF2.
characters by choosing the appropriate attribute value
for the character. When a character is shadowed, a
shadow pixel is added to the lower right edges of the
color 1 image, as shown in Figure 21. The color of the
shadow is determined by the value in the color palette
register EF3, which is normally set to black.
characters. When a character is bordered, a border pixel
is added at every horizontal, vertical or diagonal transi-
tion between color 0 and color 1. See Figure 22. The
color of the border is determined by the value in the color
palette register EF3 (normally black).
within the character except the button box pixels which
have been overwritten will alternately switch to color 0
and then back to the correct color at a rate determined
by the microcontroller through the I
interface.
2
C compatible interface. The raised pixel
2
C compatible
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