LM1276 National Semiconductor Corporation, LM1276 Datasheet - Page 21

• Manufacturer Part Number: LM1276
• Description: 150 Mhz I2c Compatible Rgb Preamplifier With Internal 512 Character Osd Rom, 512 Character Ram And 4 Dacs
• Manufacturer: National Semiconductor Corporation

Video Detection for Auto-Sizing & Auto-Centering
Auto Size Calculation Instruction Sequence
PLL Lock Detect and Horizontal
Input Select
During the monitor initialization routine by the MCU, register
bit 0xFFFD[3] must be set high. This bit is only set low during
OSD display operation and auto size calculations. Please
see the instructions above for Auto Size calculations.
The following sequence which involves register 0xFFFD and
0xFFF8 must be done by the MCU when the OSD is en-
abled. Register bits, 0xFFF8[5:4], control the PLL lock detect
override function.
Before writing to memory to setup the OSD, or
enabling OSD:
Before disabling OSD:
• Set register bits 0xFFF8[5] and 0xFFF8[4] to high
• Set register bits 0xFFFD[3] to low
• Set register bit 0x8400[6] to high
• Wait for 0x8400[7] to become high by itself
• When 0x8400[7] is high, then read auto size data regis-
• Set register bits 0xFFFD[3] to high
• Set register bits 0xFFF8[5] and 0xFFF8[4] to low
• Set register bit 0x8400[0] to high
• Set register bits 0xFFF8[5] and 0xFFF8[4] to high
• Set register bits 0xFFFD[3] to low
• Initialize OSD and write to memory
• Set register bits 0x8400[1] and/or 0x8400[2] to high
• Set register bits 0x8400[1] and/or 0x8400[2] to low
• Set register bits 0xFFFD[3] to high
• Set register bits 0xFFF8[5] and 0xFFF8[4] to low
• Set register bit 0x8400[0] to low
ters 0x8580 to 0x858F
FIGURE 13. Timing Intervals
21
Please see the OSD Programming section for more detailed
information or displaying OSD pages and accessing the
RAM
Hi-Brite Video Enhancement
Functional Description
The LM1276 enables a desired area of the CRT monitor
display to be enhanced for vivid TV quality images. The
LM1276 along with the software that is provided by National
Semiconductor is fully self-sufficient and independent of the
microcontroller in generating and controlling Hi-Brite win-
dows.
HI-BRITE VIDEO PROCESSING
The enhancement is achieved with programmable empha-
sis, programmable center frequency, and an additional Con-
trast adjustment control that is separate from the normal
Video Contrast Control of the preamp. Having an indepen-
dent contrast control allows the user to adjust the video gain
normally, having the higher gain to have a “brighter” picture
within the Hi-Brite window. The emphasis control is used to
give more “sparkle” to the highlighted video. Video that is
processed by the emphasis control has peaking added to the
video. Both the amplitude and the duration of the peaking
are adjustable through the NSC software, optimizing the
emphasis for different video resolutions. Maximum peaking
is 20%.
EMPHASIS
Emphasis is the amount of overshoot on the video signal.
Referring to Figure 14 the overshoot is the ratio of the
overshoot voltage to the video level after the emphasis has
settled out of the output signal. The typical overshoot is
about 20%. The peak measurement is taken 9 ns from the
rising edge. This delay gives a more accurate peak mea-
surement by avoiding any ringing that may occur at the rising
edge. Overshoot is defined in percent as:
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20096953
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