參數(shù)資料
型號(hào): LM1270N
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(chǎng)致200兆赫與I2C兼容的RGB視頻自動(dòng)上漿圖像增強(qiáng)
文件頁(yè)數(shù): 10/27頁(yè)
文件大?。?/td> 1302K
代理商: LM1270N
Functional Description
(Continued)
The LM1270 has the counters required to locate the clamp
pulse to any position on the horizontal line. Normally this pin
would be used as an output and be connected to the video
pre-amps. Now the clamp pulse location can be optimize for
the video channel.
Note:
When using this pin as an output a
1 k
series resistor must be used to protect the output stage
of the clamp circuit. It is also recommended to connect a
10 k
resistor between this pin and ground for more reliable
operation.
Video Detection
MODES OF OPERATION
Three modes of operation are possible with the video detect
circuit:
1.
Autosizing mode: in this mode the LM1270 takes the
measurements necessary for the monitor to perform the
autosizing operation. The horizontal flyback is used as
the reference for timing. The resultant horizontal outputs
are the flyback time, the position of the start of video
relative to the flyback end and the time from the end of
the active video to the start of the flyback time. Since the
total line time is known the microcontroller can calculate
the active video time. Now the microcontroller can cen-
ter the video between the start and end of flyback for
best image centering, and to calculate the duty cycle of
the video with respect to the forward scan time, thus
giving a measure of the relative size of the image. For
best performance in autosizing mode, it is recom-
mended that the maximum pixels per line mode is used
when measurements are made.
2.
Window calibration mode: in this mode, the horizontal
sync is used as the reference for timing. The resultant
horizontal outputs are the horizontal sync time and the
back porch and active image video time that can subse-
quently be used in conjunction with the image position
data. The image pixel per line value should be used to
set the PLL.
3.
Video data transfer: in this mode, data is sent from the
PC to the monitor on the first active video line.A72 pulse
clock string is sent on one video channel. Data is sent on
a second video channel. A window signal that tracks the
actual highlight window is sent on the third video chan-
nel. The timing parameters of this window signal are
timed by the video detect logic and stored in a special
register set. The relationship between these three sig-
nals is shown in
Figure 3
.
The selection of which video channel contains which signal
is programmed by the D_CNTL register.
IMAGE CALIBRATION MODE
Two registers are used for each axis to control the window
enable signal, WIN_EN. The first register HW_START
(VW_START) defines the period in pixels (lines) from the
leading edge of the Hsync (Vsync) to the start of the window.
The second register HW_END (VW_END) defines the dura-
tion of the highlight window. Each of these registers is de-
fined as two byte values, as per the table below:
The microcontroller must write the values of these registers,
after it has received the window position information from the
PC. However, the PC may reference this information in any
of the following ways:
1.
Leading edge of sync
2.
Trailing edge of sync
3.
Start of the video image
In order to accommodate different modes of operation, the
video detect function may be used to measure the sync
width, and the back porch (i.e., trailing edge of sync to start
of video) periods in horizontal pixels, or vertical lines for
window position calibration. The video detect function must
be set to measure with reference to the horizontal sync.
If the leading edge of sync is used as the reference for the
window start timing from the PC application, then the start
values can be directly written to the registers HW_START
and VW_START.
If the trailing edge of sync is used as the reference for the
window start timing from the PC application, then the micro-
controller should add the measured sync durations from the
video detect registers to the timing values supplied by the
PC application before writing to the HW_START and
VW_START registers.
If the start of video image is used as the reference for the
window start timing from the PC application, then the micro-
controller will add the measured sync duration and the back
porch duration from the video detect registers to the timing
values supplied by the PC application before writing to the
HW_START and VW_START registers.
In each case, it may also be necessary to modify the window
position values by adding or subtracting a value to compen-
20063520
FIGURE 3. Data, Clock and Window Signals
L
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