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ST92195 ST92T195 ST92E195 - 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 27.4s 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
of
1E3C1F(h)
or
000111100011110000011111
using
a
5MHz
clock.
If the start code is not recognised 14.3 +/- 0.2 s
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
(0=000111 or 1=111000) 6 elements @ 5MHz
B(1) Aspect Ratio Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(2) Aspect Ratio Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(3) Aspect Ratio Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
Data Group 2 Bits:
B(4) Enhanced Services Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(5) Enhanced Services Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(6) Enhanced Services Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(7) Enhanced Services Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
Data Group 3 Bits:
B(8) Subtitles Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(9) Subtitles Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(10) Subtitles Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
Data Group 4 Bits:
B(11) Reserved Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(12) Reserved Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
B(13) Reserved Bit
(0=000111 or 1=111000) 6 elements @ 5MHz
The WSS signal ends on the first half of line 23.
Total time = 137 elements @ 5 MHz. The second
half of line 23 contains video that is not related to
WSS.