LM1276AAA National Semiconductor, LM1276AAA Datasheet - Page 22

• 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

www.national.com
Hi-Brite Video Enhancement
Functional Description
Bits 0 to 2 in registers 0x85C8, 0x85CA, or 0x85CC control
the emphasis. When a “4” is programmed into these bits the
overshoot is typically 11%. A “0” will give no overshoot in the
Hi-Brite window.
CENTER FREQUENCY
Shown in Figure 15 is how the center frequency is mea-
sured. The center frequency is expressed as the time it takes
the overshoot to settle to within 5% of the DC level of the
pulse.
FIGURE 15. Center Frequency Measurement
FIGURE 14. Overshoot Measurement
(Continued)
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Bits 4 to 7 in register 0x85C1 control the center frequency.
When an “8” is programmed into 0x85C1[7:4] the t
is typically 80 ns. An “F” will give about 145 ns. A “0” will give
no emphasis in the Hi-Brite window.
HI-BRITE USER MODES
There are 3 different modes whose settings are to be preset
by the MCU. Text Mode, Movie Mode, and Picture Mode
each have their own HiBrite Contrast and Overshoot regis-
ters (See the Preamp Interface Registers Table). When the
user selects a particular mode, the preset register settings of
that mode become in effect. There is also a 4th mode, which
is the Custom Mode. The Custom Mode, however can be
adjusted by the user through the HiBrite Software, and is not
preset by the MCU. These modes can ONLY be selected or
changed from one to another through the HiBrite Software.
There is no I
default mode for the LM1276 is the Movie Mode. Thus, the
Contrast and Overshoot settings that will be in effect when a
window is initially drawn or when the Full Screen HiBrite
function is called will be that of the settings preset for the
Movie Mode.
FULL SCREEN HI-BRITE
The LM1276 is capable of applying HiBrite on the entire
screen without the need for Software. In the absence of
Software, this provides an alternative means of achieving
emphasis and contrast boost on the picture through I
contrast setting and overshoot that will be applied when this
function is enabled will be that of the previously selected
User mode, during the last instance that the software was in
operation. For example, if the user last selected the Picture
Mode in the Software preference menu, before exiting the
program, then the subsequent enabling of the Full Screen
function through I
being in effect on the full screen. The I
function are 0x8590[5:4]. Setting 0x8590[5] high will disable
the HiBrite Window Generation circuit that works together
with the Software, and 0x8590[4] enables the Full Screen
HiBrite. The Window Generation Circuit must be shut off by
0x8590[5] in order for 0x8590[4] to have an effect. Thus, to
activate the Full Screen feature, simply set 0x8590[5:4] to
high, and to deactivate, set 0x8590[5:4] to low.
HI-BRITE WINDOW GENERATION OPTIONS
Up to 8 separate windows can be drawn and enabled simul-
taneously, with programmable sizes and coordinates. The
Hi-Brite video enhancement can also be applied to the entire
desktop rather than to a specific window area or it can be
applied to everything outside of the drawn window(s). All of
this window programming can be achieved with National
Semiconductor’s software, and does not require any inter-
facing with a microcontroller.
2
C register to select the effective mode. The
2
C will result in the Picture Mode settings
2
C bits that enable this
Center Freq
2
C. The