LM1276AAA National Semiconductor, LM1276AAA Datasheet - Page 23

• Manufacturer Part Number: LM1276AAA
• 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
PAGE OPERATION
Figure 16 shows the block diagram of the OSD generator.
OSD screens are created using any of the 512 predefined
characters stored in the mask programmed ROM. The
LM1276 offers a full 9-bit character code operation, which
allows the entire 512 ROM character set to be displayed at
once. The 9-bit character code operation enables all 512
character addresses to be independently accessed on one
page.
OSD ROM CONFIGURATION
The OSD ROM is equivalent to two 256 character ROMs of
the type used in the LM1253A and LM1237. Each ROM can
be considered as a group of 3 banks, (192) two-color char-
acters followed by 1 bank (64) four-color characters. Physi-
cally, the combined ROM is then 192x2 + 64x4 + 192x2 +
64x4.
END-OF-LINE AND END-OF-SCREEN CODES
Please refer to the LM1247 datasheet for details.
BLANK CHARACTER REQUIREMENT
Five of the 512 Character ROM should be reserved as blank.
ROM Addresses 0 and 1 are for the use of the End-Of-
Screen and End-Of-Line characters as mentioned above.
ROM addresses 32, 63, and 511 must be reserved for test
FIGURE 16. OSD Generator Block Diagram
23
engineering purposes. All other ROM addresses are usable,
and any that are unused must be filled with at least a
duplicate character. Any other addresses except for those
listed above should not be left blank.
DISPLAYING AN OSD IMAGE
Consecutive lines of characters make up the displayed win-
dow. These characters are stored in the page RAM through
the I
characters up to the limit of the displayable line length (de-
pendent on the pixels per line register), although some re-
strictions concerning the enhanced features apply on char-
acter lines longer than 32 characters. The number of
characters across the width and height of the page can be
varied under I
characters that can be stored and displayed on the screen is
limited to 512 including any End-of-Line and End-of-Screen
characters. The horizontal and vertical start position can also
be programmed through the I
WINDOWS
Please refer to the LM1247 datasheet for details.
OSD VIDEO DAC
The Gain of the OSD DAC is now programmable by a 3 Bit
OSD contrast register, for 8 levels.
2
C compatible bus. Each line can contain any number of
2
C compatible control, but the total number of
2
C compatible bus.
www.national.com
20096927