ST92195C STMicroelectronics, ST92195C Datasheet - Page 149

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

ST92195C/D - TELETEXT SLICER AND ACQUISITION UNIT
TELETEXT SLICER AND ACQUISITION UNIT (Cont’d)
7.7.3.2 Signal Windows
TXTEN (TXSCR.7) is the Teletext Enable bit. Set-
ting this bit allows the slicer to check for the pres-
ence of Teletext data. The search for data is from
line 6 to line 22 for field 1 and from line 318 to line
335 for field 2. The search window's timing is de-
fined by the signal generated by the Sync Extrac-
tor. Information from this signal is found on the bit
TXTSW (Teletext Search Window, TXSCR.3). An
extended search can be done by enabling TXTES
(Teletext Extended Search, TXSCR.6). When this
bit is enabled, the search in field 1 will start on line
2 and in field 2 on line 315.
During each search interval’s TV line the slicer
looks for the presence of the Run-In-Clock. When
the Run-In-Clock is found, data extraction is per-
formed and the Teletext Data (TTD) and Clock
(TTC) are sent to the Acquisition Unit. Enabling
the TTC clock is done using the SLCCR.7 bit. Re-
fer to the Timing and Clock Controller Chapter.
If the Run-In-Clock is not found within 12 µsecs.
from the horizontal synchro leading edge, all data
processing is stopped and no FRWND (Framing
Code Window) is generated. See
The Teletext Slicer generates the FRWND control
signal. This signal defines when the Acquisition
Unit must check for the presence and validity of
the framing code.
The FRWND is activated at the end of the running
clock and it lasts 24 teletext data bits.
The Slicer uses the Teletext slicer clock generated
by the Timing Controller. This clock must be ena-
bled before enabling the Slicer to guarantee cor-
rect behaviour. To synchronize all the control sig-
Figure 89. Framing Window Timing (FRWND)
n
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FRWND
CVBS
Line Sync Pulse
Figure
88.
Color Burst
( -1.0µs / +0.4 µs)
nals on a TV line base, the Horizontal Sync
(Hcvbs) from the Sync Extractor is used.
7.7.4 Acquisition Unit
When Teletext data are available, they are broad-
cast during the Video blank interval (VBI).
During the Teletext window, the Teletext Slicer
sends to the Acquisition Unit:
– TTC clock (at 6.9375 MHz)
– TTD serial data flow
– FRWND signal which enables the framing code
This FRWND signal is provided to the Acquisition
Unit only during the TV lines that may contain
Teletext data.
12 µs
search within a precise window for each TV line
Run-In
Clock
24 Teletext Data bits
Framing
Code
Teletext data
VR02109E