ST92195D datasheet(151/249 Pages) STMICROELECTRONICS

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ST92195C/D - TELETEXT SLICER AND ACQUISITION UNIT

TELETEXT SLICER AND ACQUISITION UNIT (Cont’d)

7.7.4.1 Data Extraction and Synchronization

Teletext data extraction is based on synchroniza-

tion signals from the CVBS1 input video composite

signals (Hcvbs and Vcvbs).

Teletext data storage into the internal TDSRAM is

synchronized with the sync signals, HSYNC/

VSYNC, delivered by the chassis and also called

"deflection sync signals". The storage of the data

can be done during the whole field.

In practice, a significant phase shift of a few TV

lines may appear between the deflection sync sig-

nals and the CVBS ones.

A Teletext data acquisition window is opened on

line 6 of field 1 and line 317 of field 2 from the

CVBS signal (refer to Figure 90).

The Teletext data storage is done independently

of the phase shift.

Figure 91. Deflection / CVBS Timing

625 1

(315)

(316)

(317)

(318)

(319)

(335)

(336)

(337)

(338)

(339)

Vcvbs

Hcvbs

FRWND (field 1)

625 1

(315)

(316)

(317)

(318)

(319)

(335)

(336)

(337)

(338)

(339)

V deflection

H deflection

Teletext Slicing window (field 1)

Teletext Slicing window (field 2)

VR02109B

(Always active)

FRWND (field 2)

Acquisition / RAM

Storage

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