LM1237 National Semiconductor Corporation, LM1237 Datasheet - Page 16

• Manufacturer Part Number: LM1237
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 254 Character Osd And 4 Dacs
• Manufacturer: National Semiconductor Corporation

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OSD Generator Operation
OSD VIDEO TIMING
The OSD SELECT signal switches the source of video infor-
mation within the preamplifier from external video to the
internally generated OSD video.
WINDOWS
Two separate windows can be opened, utilizing the data
stored in the page RAM. Each window has its own horizontal
and vertical start position, although the second window
should be horizontally spaced at least two character spaces
away from the first window, and should never overlap the
first window when both windows are on. The OSD window
must be placed within the active video.
CHARACTER CELL
Each character is defined as a 12 wide by 18 high matrix of
picture elements, or ‘pixels’. The character font is shown in
Figure 25. There are two types of characters defined in the
character ROM:
FIGURE 13. Block Diagram of OSD DACs
(Continued)
16
1. Two-color: There are 190 two-color characters. Each
2. Four-color: There are 64 four-color characters stored in
pixel of these characters is defined by a single bit value.
If the bit value is 0, then the color is defined as ‘Color 1’
or the ‘background’ color. If the bit value is 1, then the
color is defined as ‘Color 2’, or the ‘foreground’ color. An
example of a character is shown in Figure 14.
the character ROM. Each pixel of the four-color charac-
ter is defined by two bits of information, and thus can
define four different colors, Color 1, Color 2, Color 3, and
Color 4. Color 1 is defined as the ‘background’ color. All
other colors are considered ‘foreground’ colors, although
for most purposes, any of the four colors may be used in
any way. Because each four-color character has two
bits, the LM1237 internally has a matrix of two planes of
ROM as shown in Figure 15.
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