LM1276 datasheet(21/50 Pages) NSC

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Video Detection for Auto-Sizing & Auto-Centering (Continued)

Auto Size Calculation Instruction Sequence

•

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-

ters 0x8580 to 0x858F

•

Set register bits 0xFFFD[3] to high

•

Set register bits 0xFFF8[5] and 0xFFF8[4] to low

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:

•

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

Before disabling OSD:

•

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

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:

20096953

FIGURE 13. Timing Intervals

LM1276 Datasheet(PDF) 21 Page - National Semiconductor (TI)

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