STV0118 datasheet(20/42 Pages) STMICROELECTRONICS

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TTXS

CKREF

TTXD

(txdl[2:0] + 2) T

CKREF

Not Valid

Bit 1

Bit 2

Figure 26 : “TTXS Rising” to “First Valid Sample” Delay for txdl[2:0] = 0

IV - FUNCTIONAL DESCRIPTION (continued)

IV.15.3 - Programming

IV.15.3.1 - ’TTXS Rising’ to ’First Valid

Sample’ Delay Programming

The encoder expects the Teletext buffer to clock out

the first Teletext data sample on the (2+N)th rising

edge of the master clock following the rising edge

of TTXS (Figure 26 depicts this graphically for

N=0). ’N’ is programmable from 0 to 7 (i.e. overall

delay is programmable from TWO to NINE 27MHz

cycles) via 3 dedicated bits located in the Configu-

ration Register4 : “txdl[2:0]”.

IV.15.3.2 - Teletext Line Selection

Five dedicated registers allow to program Teletext

encoding in various areas of the Vertical Blanking

Interval (VBI) of each field. A total of 4 such areas

(i.e. blocks of contiguous Teletext lines) can inde-

pendently be defined within the two VBIs of one

frame (e.g. 2 blocksin each VBI, or 3 blocks in field1

VBI and one in field2 VBI, etc.). Further, under

certain circumstances, it is possible to define up to

4 areas in each VBI.

Programming is performed using 4 “Teletext Block

De f ini ti on” r egis t er s ( T TXBD 1, T T XBD 2,

TTXBD3,TTXBD4) and a “Teletext Block Mapping”

registers 34 to 38 for details.

IV.15.4 - Teletext Pulse Shape

The shape and amplitude of a single Teletext pulse

are depictedin Figure27, its relativepower spectral

density is given in Figures 28 and 29 and is sub-

stantially zero at frequencies above 5MHz, as re-

-150

-100

-50

100

150

(ns)

+144ns

-144ns

Figure 27 : Shape and Amplitude of a Single

Teletext Symbol

34567

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

(x106) (Hz)

Figure 28 : Linear PSD Scale

quired by the World System Teletext specification.

STV0118

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