9397 750 14325 © Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Product data sheet Rev. 03 — 9 December 2004 46 of 55
Philips Semiconductors
SAA7128H; SAA7129H
Digital video encoder
10.2 Teletext timing
Time t
FD
is the time needed to interpolate input data TTX and insert it into the CVBS and
VBS output signal, such that it appears at t
TTX
= 9.78 µs (PAL) or t
TTX
= 10.5 µs (NTSC)
after the leading edge of the horizontal synchronization pulse.
Time t
PD
is the pipeline delay time introduced by the source that is gated by TTXRQ in
order to deliver TTX data. This delay is programmable by register TTXHD. For every active
HIGH state at output pin TTXRQ, a new teletext bit must be provided by the source (new
protocol) or a window of TTXRQ going HIGH is provided and the number of teletext bits,
depending on the chosen teletext standard, is requested at input pin TTX (old protocol).
Since the beginning of the pulses representing the TTXRQ signal and the delay between
the rising edge of TTXRQ and valid teletext input data are fully programmable (TTXHS
and TTXHD), the TTX data is always inserted at the correct position after the leading edge
of outgoing horizontal synchronization pulse.
Time t
i(TTXW)
is the internally used insertion window for TTX data; it has a constant length
that allows insertion of 360 teletext bits at a text data rate of 6.9375 Mbit/s (PAL),
296 teletext bits at a text data rate of 5.7272 Mbit/s (WST) or 288 teletext bits at a text
data rate of 5.7272 Mbit/s (NABTS). The insertion window is not opened if the control bit
TTXEN is logic 0.
Using appropriate programming, all suitable lines of the odd field (TTXOVS and TTXOVE)
plus all suitable lines of the even field (TTXEVS and TTXEVE) can be used for teletext
insertion.
Fig 23. Teletext timing
t
i(TTXW)
t
TTX
t
PD
t
FD
CVBS/Y
TTX
TTXRQ (new)
TTXRQ (old)
text bit #: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
mhb504
