SAA7120H Datasheet, PDF (28/36 Pages) NXP Semiconductors – Digital video encoder

Philips Semiconductors
Digital video encoder
Product specification
SAA7120H; SAA7121H
8.2 Teletext timing
Time t_FD is the time needed to interpolate input data TTX
and insert it into the CVBS and Y 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.
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_TTXWin 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 Mbits/s (PAL),
296 teletext bits at a text data rate of 5.7272 Mbits/s (WST)
or 288 teletext bits at a text data rate of 5.7272 Mbits/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.
handbook, full pagewidth
CVBS/Y
TTX
TTXRQ
tTTX
tTTXWin
textbit #: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
tPD
tFD
Fig.10 Teletext timing.
MBH788
2002 Oct 11
28