SAA7182A Datasheet, PDF(38/45 Page) NXP Semiconductors

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SAA7182A Datasheet, PDF (38/45 Pages) NXP Semiconductors – Digital Video Encoder EURO-DENC2

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Philips Semiconductors

Digital Video Encoder (EURO-DENC2)

Preliminary speciï¬cation

SAA7182A; SAA7183A

Teletext timing

Time tFD is the time needed to interpolate input data TTX

and inserting it into the CVBS and Y output signal, such

that it appears at tTTX = 10.2 Âµs after the leading edge of

the horizontal synchronization pulse.

Time tPD is the pipeline delay time introduced by the

source that is gated by TTXRQ in order to deliver TTX

data.

Since the pulse representing the TTXRQ signal is fully

programmable in duration and rising/falling edges (TTXHS

and TTXHE), the TTX data is always inserted at the correct

position of 10.2 Âµs after the leading edge of outgoing

horizontal synchronization pulse.

Time tTTXWin is the internally used insertion window for

TTX data; it has a constant length that allows insertion of

360 teletext bits (maximum) at a text data rate of

6.9375 Mbits/s. The insertion window is not opened if the

control bit TTXEN is zero.

Thus 37 TTX bits correspond to 144 LLC clocks, each bit

has a duration of nearly 4 LLC clocks. The chip-internal

sequencer and variable phase interpolation filter

minimizes the phase jitter, and thus generates a

bandwidth limited signal, which is digital-to-analog

converted for the CVBS and Y outputs.

At the TTX input, bit duration scheme repeats after 37 TTX

bits or 144 LLC clocks. The protocol demands that TXX

bits 10, 19, 28 and 37 are carried by three LLC samples,

all others by four LLC samples. After a cycle of 37 TTX

bits, the next bits with three LLC samples are bits 47, 56,

65 and 74; this scheme holds for all succeeding cycles of

37 TTX bits, until 360 TTX bits (including 16 run-in bits)

are completed. For every additional line with TTX data, the

bit duration scheme starts in the same way.

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.

TELETEXT PROTOCOL

The frequency relationship between TTX bit clock and the

system clock LLC for 50 Hz field rate is given by the

relationship of line frequency multiples, which means

1 728/444.

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

4 3 4 1/LLC

MGB701

1996 Oct 02

Fig.19 Teletext timing diagram.

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