Analog Devices EE203 Application Notes
Engineer To Engineer Note EE-203
a
Technical Notes on using Analog Devices' DSP components and development tools
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Interfacing the ADSP-BF535/ADSP-BF533 Blackfin® Processor to
NTSC/PAL video decoder over the asynchronous port
Contributed by Thorsten Lorenzen September 1, 2003
Introduction
The purpose of this note is to describe how to
hook up video devices such as the ADV7183
NTSC/PAL Video Decoder to the external bus of
the ADSP-BF535 Blackfin® Processor. Because
of its architecture and video processing
capabilities, Blackfin will interface with video
devices. The ADSP-BF535 as the first part of the
Blackfin Processor family is not equipped with a
standard interface that glueless interacts with
video devices, but as this EE-Note shows, the
Asynchronous Interface can be used to receive
video data in ITU-656 format.
Future Blackfin derivatives will be
equipped with interfaces designed to
support video devices (PPI interface).
ADV7183 NTSC/PAL Video Decoder
The ADV7183 is an integrated video decoder
that automatically detects and converts a
standard analog base band television signal
compatible with world wide standards NTSC or
PAL into 4:2:2 or 4:1:1 component video data
compatible with 16-bit/8-bit CCIR601/CCIR656
or 10/20-bit extended standards.
The advanced and highly flexible digital output
interface enables performance video decoding
and conversion in both frame buffer based and
line locked based systems “LLC Mode”. This
makes the device ideally suited for a broad rage
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of applications with diverse analog video
characteristics including tape based sources,
broadcast sources, security/surveillance cameras
and professional systems.
Basics of analog video composite signals
To fully understand the decoders digital output it
is helpful to review the background of the NTSC
standard and how it came along. If you are
familiar with it already please go to the next
chapter.
The first color television system was developed
in the United States and began broadcasting in
1954. For economic reasons, a requirement was
made that monochrome receivers must be able to
display the black and white portion of a color
broadcast and that color receivers must be able to
display monochrome broadcast. For broadcasting
purposes all required signals must be fitted into a
single line. However, the CVBS signal looks still
as years ago for compatibility purposes.
The analog composite video signal was designed
a way it is shown as follows.
Imagine, a CRT (Cathode Ray Tube) of a TV
such as shown in Figure 1 has been designed to
display a video image based on N lines in the
visual area “active video” of the monitors
surface. In general, the ray of the CRT starts at
the top left side and goes to the right. After
reaching the right end it turns off and goes back
a
k
to the left, a line below. Reaching the left side it
turns on again and draws the next line on the
screen. By repeating this the monitor will always
be drawn with the help of the CRTs ray.
What kind of signals are required to fully drive
the CRT?
Even Field Odd Field
Line 1
Line 3
.
.
Last Line
Line 2
Line 4
.
.
Last Line
In Figure 1 a NTSC Video Composite Signal can
be seen. It drives the CRT in a sense that it runs
as discussed above.
Line 1 Line 3
CVBS
Figure 1: Multiple lines of an analog video composite signal (CVBS)
In general the video composite signal has two
major tasks.
First, the CRT (Figure 1) runs from the left to
the right, from the top to the bottom controlled
by its own oscillators and sidetrack units. But it
must be controlled (triggered) by signals that
comes along (is aligned to) with the signal that
holds the image data. Otherwise the image can
never be placed on the screen in a correct order.
Such signals are called:
Horizontal Sync (Line Blanking Signal), to
force the CRT to turn off the ray and start
with the next line. The Line Blanking area in
Figure 2 shows such a signal.
Vertical Sync, to force the CRT to turn off the
ray at the end of a frame/field and start with
the next frame/field. The right end of the
CVBS signal on Figure 1 “Blank” shows such
a signal.
Second
luminance and chrominance information’s “(Y)
.Blan
Last Line
, the image data is split into parts of
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a
(C)”. “Figure 2” shows the two information’s
combined with the syncs in a single line.
Luminance: As it can be seen in the area of
“Active Video Line” the steps show different
levels of luminance displaying a bar of
different values in brightness.
Chrominance: The gray squares in Figure 2
represents 9 cycles of a 3.58MHz frequency
as shown underneath the signal. The cycles
are carrying the color information. The first
gray square in the area of Color Burst drives
an extra oscillator build into the video
receiver and holds the cycles as a reference.
The following squares “cycles” will be
compared with the reference (Color Burst).
The phase shift between these determines the
hue. Color saturation is implemented by the
cycles amplitude.
Line Blanking Active Video Line
Color Burst
Decoding the analog composite video signal by the ADV7183 in LLC mode
It has been discussed how the analog composite
video signal looks like. This section is dedicated
to understand the signal path of the decoder
when in CVBS mode. Just one of the two ADCs
are used for conversion
After the analog signal has passed the ADC it
goes into a luminance path to separate the
luminance information. Also, it goes into a
chrominance path to separate the chrominance
information.
In the luminance path the 10-bit data from the
ADC is applied to an antialiasing low pass filter
that is designed to band-limit the input video
signal such that antialiasing does not occur. In
CVBS mode a notch filter must be used to
remove the unwanted chrominance data that lies
around the subcarrier. The next step is a peaking
filter. This filter offers a sharpness function on
the luminance path. The data is then passed
through a resampler to correct for linelength
variations in the input video. The resampler is
designed to always output 720 pixels per line.
In the chrominance path the 10-bit data from the
ADC is first demodulated as it is achieved by
multiplying the locally generated quadrature
subcarrier, where the sign of the cos subcarrier is
inverted from line to line according to the PAL
switch. The low pass filter is applied to remove
components at twice the subcarrier frequency.
The chrominance data is then passed through an
band-pass filter to remove unwanted luminance
Figure 2: One line of a Video Composite Video Signal
As many as lines the video resolution includes as
many line signals must be implemented in the
video composite signal.
Interfacing the ADSP-BF535/ADSP-BF533 Blackfin® Processor to NTSC/PAL video decoder over the
asynchronous port (EE-203) Page 3 of 12
data. After a shaping filter is applied the data is
passed through a resampler to correct for line
length variations in the input video. It always
outputs 720 pixels per line.
The output formatter block does take the
luminance and chrominance data and put it in the
order as it is shown in Figure 3.
a
As is can be seen the actual video data has been
embedded in the data block (Active Video).
Active video data is separated by blanking and
synchronization. Due to the ITU-656
recommendation it always begins and ends with
the preamble (“FF 00 00 DA” 10 80 10 80 … 10
80 10 80 “FF 00 00 C7”).
Even Field Odd Field
Line 1
Line 2
.
.
Last Line
Figure 13 shows a video stream blanking and the
preamble included.
Alternatively, the synchronization values
embedded in the data stream can also be
provided with the help of external lines “pins”.
Figure 3 show such lines “DV, VREF, HREF”.
Line 2
Video Video Video
Blank Blank Blank
.
CVBS
16-bit
BUS
HREF
DV
VREF
Line 1
Video
Blank
Figure 3: Analog input and digital output of an video decoder
.
Last Line
Video
Blank
Blank
t
Interfacing the ADSP-BF535/ADSP-BF533 Blackfin® Processor to NTSC/PAL video decoder over the
asynchronous port (EE-203) Page 4 of 12
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