Philips Semiconductors
Product specification
Digital video encoder
7.3.2
T
ELETEXT INSERTION AND ENCODING
7.4
SAA7128H; SAA7129H
RGB processor
Pin TTX receives a WST or NABTS teletext bitstream
sampled at the LLC clock. Two protocols are provided:
•
At each rising edge of output signal (TTXRQ) a single
teletext bit has to be provided after a programmable
delay at input pin TTX
•
The signal TTXRQ performs only a single LOW-to-HIGH
transition and remains at HIGH level for 360, 296 or 288
teletext bits, depending on the chosen standard.
Phase variant interpolation is achieved on this bitstream in
the internal teletext encoder, providing sufficient small
phase jitter on the output text lines.
TTXRQ provides a fully programmable request signal to
the teletext source, indicating the insertion period of
bitstream at lines which are selectable independently for
both fields. The internal insertion window for text is set to
360 (PAL-WST), 296 (NTSC-WST) or 288 (NABTS)
teletext bits including clock run-in bits. The protocol and
timing are illustrated in Fig.23.
7.3.3
V
IDEO
P
ROGRAMMING
S
YSTEM
(VPS)
ENCODING
This block contains a dematrix in order to produce red,
green and blue signals to be fed to a SCART plug.
Before Y, C
B
and C
R
signals are de-matrixed, individual
gain adjustment for Y and colour difference signals and
2 times oversampling for luminance and 4 times
oversampling for colour difference signals is performed.
The transfer curves of luminance and colour difference
components of RGB are illustrated in Figs 12 and 13.
7.5
SECAM processor
SECAM specific pre-processing is achieved in this block
by a pre-emphasis of colour difference signals (for gain
and phase see Figs 14 and 15).
A baseband frequency modulator with a reference
frequency shifted from 4.286 MHz to DC carries out
SECAM modulation in accordance with appropriate
standard or optionally wide clipping limits.
After the HF pre-emphasis, also applied on a DC reference
carrier (anti-Cloche filter; see Figs 16 and 17), line-by-line
sequential carriers with black reference of 4.25 MHz (Db)
and 4.40625 MHz (Dr) are generated using specified
values for FSC programming bytes.
Alternating phase reset in accordance with SECAM
standard is carried out automatically. During vertical
blanking the so-called bottle pulses are not provided.
7.6
Output interface/DACs
Five bytes of VPS information can be loaded via the
I
2
C-bus and will be encoded in the appropriate format into
line 16.
7.3.4
C
LOSED CAPTION ENCODER
Using this circuit, data in accordance with the specification
of closed caption or extended data service, delivered by
the control interface, can be encoded (line 21). Two
dedicated pairs of bytes (two bytes per field), each pair
preceded by run-in clocks and framing code, are possible.
The actual line number where data is to be encoded in, can
be modified in a certain range.
The data clock frequency is in accordance with the
definition for NTSC-M standard 32 times horizontal line
frequency.
Data LOW at the output of the DACs corresponds to 0 IRE,
data HIGH at the output of the DACs corresponds to
approximately 50 IRE.
It is also possible to encode closed caption data for 50 Hz
field frequencies at 32 times horizontal line frequency.
7.3.5
A
NTI
-
TAPING
(SAA7128H
ONLY
)
In the output interface, encoded Y and C signals are
converted from digital-to-analog in a 10-bit resolution.
Y and C signals are also combined to a 10-bit CVBS
signal.
The CVBS output occurs with the same processing delay
(equal to 82 LLC clock periods, measured from MP input
to the analog outputs) as the Y, C and RGB outputs.
Absolute amplitude at the input of the DAC for CVBS is
reduced by
15
⁄
16
with respect to Y and C DACs to make
maximum use of conversion ranges.
Red, green and blue signals are also converted from
digital-to-analog, each providing a 9-bit resolution.
Outputs of the DACs can be set together via software
control to minimum output voltage (approximately 0.2 V
DC) for either purpose. Alternatively, the buffers can be
switched into 3-state output condition; this allows for ‘wired
AND’ing with other 3-state outputs and can also be used
as a power-save mode.
For more information contact your nearest Philips
Semiconductors sales office.
2000 Mar 08
11
PHILIPS [ NXP SEMICONDUCTORS ]
