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參數(shù)資料
| 型號： | LM1270 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Hi-Brite 200 MHz I2C Compatible RGB Image Enhancer with Video Auto Sizing |
| 中文描述： | 高亮度場致200兆赫與I2C兼容的RGB視頻自動上漿圖像增強 |
| 文件頁數(shù)： | 8/27頁 |
| 文件大?。?/td> | 1302K |
| 代理商： | LM1270 |
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Functional Description
VIDEO SECTION
The LM1270 gives the monitor designer the ability to add a
highlighted window to the CRT monitor. Special software
provided manufacturer enables the user to select the area
he wants to have highlighted. National Semiconductor refers
to this feature as Hi-Brite. Referring to
Figure 1
, the Block
Diagram of the LM1270, note that there are two channels for
each video input. Of the three video channels only the blocks
of the blue channel are shown since all three channels have
the same blocks. A buffer stage is located at the video inputs
and this is followed by a contrast control. Referring to chan-
nel one (B1 input), the contrast control is followed by an
emphasis block. The combination of the emphasis control
and the contrast control gives the desired highlighted video
inside the Hi-Brite window. The output of the emphasis stage
and the output of the contrast control in channel two go to a
high-speed video switch, which selects the video channel
going to the output stage.
Having an independent contrast control in each video chan-
nel allows the user to adjust the video gain, normally having
the higher gain in channel one, giving a “brighter” picture
within the Hi-Brite window. The Emphasis stage is used to
give more “sparkle” to the highlighted video. Video going into
the emphasis stage has peaking added to the video. Both
the amplitude and the duration of the peaking are adjustable
through the I
2
C compatible bus, optimizing the emphasis for
different video resolutions. Maximum peaking is 20%. Al-
though most uses of the Hi-Brite would be for the video
inside the selected window, the reverse may be selected
where all the video outside the window is processed through
the emphasis stage. Please remember that for all video
inputs the corresponding channel one input and the channel
two input must be shorted together. Standard AC coupling
such as used with the LM123X or LM124X pre-amps is to be
used with the LM1270.
I
2
C COMPATIBLE INTERFACE
Pins 13 and 14 receive signals from an I
2
C compatible bus.
The interface section is used to decode the I
2
C compatible
signal and update the registers. Note that all functions of the
LM1270 are controlled through an I
2
C or an I
2
C compatible
bus. Details on the internal registers are covered in the I
2
C
compatible Interface Registers Section.
PLL
Aphase locked loop (PLL) is required for the LM1270 to sync
all the timing circuits to the incoming horizontal sync. Proper
operation of both the Hi-Brite window and the video detec-
tion requires a proper lock of the PLL reference pulse to the
horizontal sync. Careful layout of the loop filter at pin 10 is
necessary for keeping noise out of the PLL section. The
register to the PLLis used to set the number of pixels per line
for the internal counters that set the Hi-Brite window, gener-
ate the internal clamp pulse, and set the counters for the
video detection. The maximum number of pixels per line is
2,047, or 7Fh. For good resolution of the window, 640 is the
recommended minimum pixels per line. The VCO has a
running frequency range of 110 MHz to 160 MHz when using
prescaler 7. For the other pre-scaler settings the frequency
range is 120 MHz to 220 MHz. The output of the VCO goes
to a pre-scaler with a 3 bit register, dividing the VCO output
by up to 8. Minimum division is 1, just a straight pass through
the pre-scaler. Calculating the VCO frequency:
F
VCO
= VCO frequency
F
H
= Horizontal line frequency
N = Number of pixels per line
M = PLL pre-scaler
Using the above terms gives the following formula for the
PLL:
F
VCO
= N
*
M
*
F
H
It is easiest to run the PLL in AUTO mode, setting bit 7 of
address 0E to a “1”. Here the user programs in the desired
pixels per line and the part will select the preferred pre-scaler
number. If one is using manual mode below is a table
showing the relationship between the pre-scaler and the
VCO frequency. The chart shows the pixel frequency, F
P
.
F
P
= F
VCO
/M
The necessary pixels per line is calculated by the following
formula:
N = F
P
/F
H
PRES
C2
1
1
1
1
0
0
0
0
PRES
C2
1
1
0
0
1
1
0
0
PRES
C2
1
0
1
0
1
0
1
0
PRES
DIV RATIO
1
2
3
4
5
6
7
8
F
P
(max)
MHz
160.0
110.0
73.3
55.0
44.0
36.7
31.4
27.5
F
p
(min)
MHz
110.0
60.0
40.0
30.0
24.0
20.0
17.1
10.0
TIMING AND WINDOW GENERATION SECTION
All timing is referenced to the vertical and horizontal sync
inputs that come in on pins 11 and 12 respectively. The two
registers near the inputs sets the start of the window for both
the horizontal and vertical direction. The window generator
and the following logic are used to generate a pulse to
control the video switch used to switch between the video
with emphasis and the standard video. The switching be-
tween the two video channels is the generation of the win-
dow seen by the user. There is the option to switch off the
Hi-Brite window. An additional switch located just before the
video switch is used to turn off the control signal.
Video detection is another important function inside the
LM1270. Note that both video channels, the PLL, and both
vertical sync and horizontal flyback signals all go to this
block. From these inputs the video detection is used to
detect the length of the horizontal and vertical front porch as
well as the length of the active video for both the horizontal
and vertical directions. This information allows the monitor
designer to offer auto alignment in his monitor. Further pro-
cessing of the video information in the video and window
timing data section generates an internal clamp pulse. This
is the DC restoration pulse for the LM1270. Pin 24 is the
output for the clamp pulse, allowing the monitor designer to
use it for the clamp input of the pre-amp. There is also the
option to program the LM1270 to accept an external clamp
pulse instead of using its own internally generated pulse.
The video detection section also has a data receiver for
receiving data encoded on the video. When this feature is
used, the MCU in the monitor is used to control the LM1270,
keeping all communication with the LM1270 within the moni-
tor. This results in a faster response time by eliminating the
need for the computer to control the LM1270. Control by the
computer requires communication through the monitor MCU.
L
www.national.com
8
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| LM1270N | Hi-Brite 200 MHz I2C Compatible RGB Image Enhancer with Video Auto Sizing |
| LM1270NA | Hi-Brite 200 MHz I2C Compatible RGB Image Enhancer with Video Auto Sizing |
| LM1279 | 110 MHz RGB Video Amplifier System with OSD |
| LM1279N | 110 MHz RGB Video Amplifier System with OSD |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1270N | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Hi-Brite 200 MHz I2C Compatible RGB Image Enhancer with Video Auto Sizing |
| LM1270NA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Hi-Brite 200 MHz I2C Compatible RGB Image Enhancer with Video Auto Sizing |
| LM1276 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs |
| LM1276AAA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:150 MHz I2C Compatible RGB Preamplifier with Internal 512 Character OSD ROM, 512 Character RAM and 4 DACs |
| LM1279 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:110 MHz RGB Video Amplifier System with OSD |
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