STV0118 datasheet(19/42 Pages) STMICROELECTRONICS

19 / 42 page

100

150

200

250

300

µs

48.7

µs

Word 1

4 bits

Word 2

4 bits

Word 0

6 bits

CRCC

6 bits

Bit 1

Bit 20

Figure 25 : Example CGMS Waveform

IV - FUNCTIONAL DESCRIPTION (continued)

The closed caption encoder considers that closed

caption data has been loaded and is valid on

completion of the write operation into register 40

for field1, into register42 for field2. If closed caption

encodinghas been enabled and no new data bytes

have been written into the closed caption data

registers when the closed caption window starts on

the appropriateTV line, then the circuit outputstwo

US-ASCII NULL characterswith odd parity after the

start bit.

IV.14 - CGMS Encoding

CGMS (Copy Generation Management System -

also known as VBID and described by standard

CPX-1204 of EIAJ) data can be encoded by the

circuit. Three bytes (20 significant bits) are deliv-

ered to the chip via the I2C interface.Two reference

bits (‘1’ then ‘0’) are encoded first, followed by 20

bits of CGMS data (including a Cyclic Redundancy

Check sequence, not computed by the device and

supplied to it as part of the 20 data bits). The

reference bits are generated locally by the

STV0118. Refer to Figure 25 for a typical CGMS

waveform.

When CGMS encoding is enabled, the CGMS (see

bit encgms in Reg 3) waveform is continously

present once in each field, on lines 20 and 283

(SMPTE-525 line numbering).

The CGMS data register is double-buffered,which

means that it can be loaded anytime (even during

line 20/283) without any risk of corrupting CGMS

data that could be in the process of being en-

coded.The CGMS encoder considers that new

CGMS data has been loaded and is valid on com-

pletion of the write operation into register 33

IV.15 - Teletext Encoding

The STV0118 is able to encode Teletext according

to the “CCIR/ITU-R Broadcast Teletext System B”

specification, also known as “World System

Teletext”.

In DVB applications, Teletext data is embedded

within DVB streams as MPEG data packets. It is the

responsibility of a “Transport Layer Processing” IC

(or demultiplexer), like SGS-Thomson’s ST20-

based “TP2”, to sort out incoming data packets and

inparticularto storeTeletextpacketin abuffer,which

then passes them to the STV0118 on request.

IV.15.1 - Signals Exchanged

The STV0118 and the Teletext buffer exchange 2

signals: TTXS (Teletext Synchronization) going

from the STV0118 to the Teletext Buffer and TTXD

(Teletext Data) going from the Teletext Buffer to the

STV0118.

The TTXS signal is a request signal generated on

selected lines. In response to this signal, the

Teletext buffer is expected to send 360 Teletext bits

to the STV0118 for insertion of a Teletext line into

the analog video signal.

The durationof the TTXS windowis 1402reference

clockperiods (51.926

µs), which correspondsto the

duration of 360 Teletext bits (see Transmission

Protocol below).

Following the TTXS rising edge the encoder ex-

pects data from the Teletext buffer after a program-

mable number (2 to 9) of 27MHz master clock

periods. Data is transmittedsynchronously with the

master clock at an average rate of 6.9375Mbit/s

according to the protocol described below. It con-

sists, in order of transmission, of 16 Clock Run-In

bits, 8 Framing Code bits and the 336 bits (42

bytes) that represent one Teletext packet.

IV.15.2 - Transmission Protocol

In order to transmit the Teletext data bits at an

average rate of 6.9375Mbit/s, which is about

1/3.89 times the master clock frequency, the follo-

wing scheme is adopted :

The 360-bit packet is regarded as nine 37-bit se-

quences plus one 27-bit sequence. In every se-

quence, each Teletext data bit is transmitted as a

succession of 4 identicalsamples at 27 Msample/s,

except for the 10th, 19th, 28th and 37th bits of the

sequence which are transmitted as a succession

of 3 identical samples. This protocol is compatible

with SGS-Thomson’s ST-20 based Tranport Layer

IC (“TP2”).

STV0118

19/42

STV0118 数据表(PDF) 19 Page - STMicroelectronics

STV0118 数据表(HTML) 19 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

数据表下载