LM1237BDBC/NA National Semiconductor, LM1237BDBC/NA Datasheet - Page 17

• Manufacturer Part Number: LM1237BDBC/NA
• Description: Video ICs, 150MHz I2C Compatible RGB Preamplifier with Internal 254 Character OSD 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 color1 and color2 in the two color attribute
table and color1, color2, color3, color4 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 combination
selections or ‘palettes’. As the look-up table can be dynami-
cally coded by the microcontroller over the I
interface, each color can be assigned to any one of 2
Plane 1
18 rows
+
FIGURE 15. A Four-Color Character
FIGURE 14. A Two-Color Character
2
(Continued)
C compatible
12 columns
9
(i.e.
Plane 2
17
512) choices. This allows a 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.
COLOR 2
COLOR 1
=
20023421
Composite
www.national.com
20023422