ST92195C STMicroelectronics, ST92195C Datasheet - Page 166

• Manufacturer Part Number: ST92195C
• Description: 48-96 Kbyte Rom Hcmos Mcu With On-screen Display And Teletext Data Slicer
• Manufacturer: STMicroelectronics

VPS & WSS SLICER (Cont’d)
7.8.2 General Operation
The VPS/WSS Slicer implements the following
features:
Wide Screen Signalling (WSS) follows the pro-
posed ETSI standard providing advanced televi-
sion features such as aspect ratio and format us-
ing 14 Bits of information extracted from Half Line
23, Field 1.
Video Programming System (VPS) follows the in-
dustry standard for VPS using 5 bytes of informa-
tion extracted from Line 16, on Field 1 (bytes 5, 11
to 14).
The input signals are treated internally by the sys-
tem as follows:
– Data: the serial data from the analog video input
– WSS window/VPS window. For the VPS signal
– VSync: The system also receives the sync sig-
7.8.2.1 Analog Input stage
The data slicer determines the average amplitude
of the input data stream and references a compa-
rator at this value. The average amplitude is ac-
complished by AC coupling the video input signal
is converted to serial digital data for digital
processing.
treatment, the analog video signal is taken from
the CVBS1 pin after its amplification through the
programmable amplifier. For the WSS signal
treatment, the video signal is taken from the
CVBS2 pin directly. The CVBS2 pin is AC driven
through a 150pF capacitor.
nals from the video input pin. This signal con-
tains the information telling exactly which line
and field is being processed. This is performed
in the Sync Extractor Cell with its outputs deliv-
ered to the VPS/WSS cell.
into the slicer cell and gating the bias circuits dur-
ing the active bi-phase signal.
7.8.2.2 Video Input Specification
The composite video baseband signal (CVBS) in-
put is 1 V
100IRE video for both CVBS1 (VPS path) and
CVBS2 (WSS path). The polarity of the video is
negative going sync.
7.8.2.3 Digital Decoder
The digital decoder uses the 5MHz clock as the
main timing reference and the digital outputs from
the sync and data slicer as the signal inputs. The
data for both VPS and WSS are transmitted with a
reference of 5 MHz clock with the same phase.
The serial digital data coming out of the data slicer
is first sampled at 5 MHz, this oversamples the
2.5Mbits/sec enough to process the signal under
normal conditions. The samples are then digitally
processed.
The bi-phase code is checked on both sides of the
signal with respect to a timing delay to detect er-
rors.
7.8.2.4 Framing Code and Data Check
If the framing code is recognized, the data is fur-
ther processed and a flag is set.
The data is then processed for biphase errors. If
the data is not defective, bits ERB1..5 remain at 0
and the data is stored. If the data is in error, bits
ERB1..5 are set by hardware. These bits must be
cleared by the user before the next framing code.
If a framing code is not recognized, the data is not
stored , the flag remains at 0 (VFRMVPS bit in the
VPSSR register) and the slicer waits for the next
VPS/WSS window.
ST92195C/D - VPS & WSS SLICER
PP
+/- 6dB from the bottom of sync to
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