ST92195D datasheet(168/249 Pages) STMICROELECTRONICS

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ST92195C/D - VPS & WSS SLICER

VPS & WSS SLICER (Cont’d)

7.8.4 About Wide-Screen-Signaling (WSS)

The main purpose of the WSS signal is to define

the aspect ratio and format of the current television

signal. This signal is needed with the use of 16:9

displays where both 4:3 and 16:9 transmissions

may be present at the same time on different

channels. The information contained in WSS de-

fines the transmitted aspect ratio and the recom-

mended display format so that the television will

automatically adjust the display for optimal view-

ing.

The WSS signal contains digital data on the first

half of line 23 of a transmitted PAL/SECAM video

signal. The WSS signal is intended to be recorded

on a video cassette recorder (VCR) during normal

recording to keep the encoded aspect ratio infor-

mation together with the program of interest. The

automatic switching of the television would occur

during the playback of the previously recorded

program. In order to support double WSS writing,

the system may slice on both lines 22 and 23. The

registers have been duplicated to deliver a second

line of WSS if available.

The signal is defined by 137 “200ns” elements for

a total of 27.4µs and is one third the VPS rate to al-

low recovery of data from VCR tapes. WSS has an

effective clock of only 1.66MHz but is still defined

using the same 5MHz clock used in the VPS sys-

tem.

7.8.5 WSS Signal Content

The parts of the signal are summarized below:

Word 1: Run-in

(1.1111.0001.1100.0111.0001.1100.0111)

29 elements @ 5MHz

The run-in word is 1F1C71C7(h) using a 5MHz

clock.

Word 2: Start code

(0001.1110.0011.1100.0001.1111)

24 elements @ 5MHz

The start code helps to define the presence of

WSS to synchronize the following data stream.

The

signal

consists

1E3C1F(h)

000111100011110000011111

using

5MHz

clock.

If the start code is not recognised 14.3 +/- 0.2 µs

after the WSSWin rising edge, the system waits for

the next WSSWin to find a Start code.

Data Bits Purpose Bi-phase Encoding Dura-

tion(1.2

Data Group 1 Bits:

B(0) Aspect Ratio Bit