LM1246AAA National Semiconductor, LM1246AAA Datasheet - Page 20
LM1246AAA
Manufacturer Part Number
LM1246AAA
Description
150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM/ 512 Character RAM and 4 DACs
Manufacturer
National Semiconductor
Datasheet
1.LM1246AAA.pdf
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OSD Generator Operation
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.
OSD VIDEO DAC
The OSD DAC is controlled by the 9-bit (3x3 bits) OSD video
information coming from the pixel serializer look-up table.
The look-up table in the OSD palette is programmed to
FIGURE 16. Block Diagram of OSD DACs
(Continued)
FIGURE 15. Bank Addressing
20
select 4 color levels out of 8 linearly spaced levels per
channel. The OSD DAC is shown in Figure 16, where the
gain is programmable by the 2-bit OSD contrast register, in 4
stages to give the required OSD signal. The OSD DACs use
the reference voltage, V
OSD VIDEO TIMING
The OSD analog signal then goes to the switch, shown in
Figure 16 and Figure 1 where the timing control switches
from input video to OSD and back again as determined by
the control registers. This is also where horizontal and ver-
tical blanking are also inserted at their appropriate intervals.
REF
, to bias the OSD outputs.
20068529
20068528
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