LM1247 National Semiconductor, LM1247 Datasheet - Page 16

• 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

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OSD Generator Operation
varied under I
characters that can be stored and displayed on the screen is
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
2
C compatible control, but the total number of
(Continued)
FIGURE 13. Bank Addressing
16
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
select 4 color levels out of 8 linearly spaced levels per
channel. The OSD DAC is shown in Figure 14, 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 14 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.
2
C compatible bus.
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