MODELS: LT-37131 / LT-37132 / LT-46131 / LT-46231
Page 15
TVGuide On-Screen (TVGOS)
When the TV is powered off it begins a process
called ‘harvesting’. There are 2 types of harvesting; one
of which is TVGuide harvesting. During this harvesting
process the TV scans through every channel and searches
for TVGOS data. This data is located in the VBI (Vertical
Blanking Interval). The TVGOS data will be located
somewhere between line 10 and line 25 of the VBI (except
line 21).
The data is provided by Gemstar and is inserted
into the VBI by the broadcaster onto a ‘host channel’. A
host channel can be any analog channel agreed upon by
Gemstar and the broadcaster. The data packets are
transmitted several times per day for several hours (This
will vary based on location). The TV must be in the OFF
state for the full duration of the transmission to receive the
data packets in their entirety.
When the harvesting begins the TV-Micro
enables the output from pin 43 of the Video Switch (see
figure1). The SUB-Y output of the video switch (IC2K01)
is tapped off and sent to a sync separator where H and V
sync are isolated and sent to the PIC Micro. The sync
signals are used for timing of the control signals sent to
IC7R04. This IC directs charge to a hold capacitor which
establishes the slicing threshold for the comparator based
on the level of the incoming SUB-Y signal. Pin 2 of the PIC
Micro provides a hold function to stabilize the H-Sync
during the vertical blank time. The SUB-Y signal is sent to
IC7R02 where the slicing is preformed. The output of
IC7R02 is serial data and is sent to Pin 1 of PIC Micro (See
figure2). This data is assembled by the PIC Micro and is
then transfered by serial communication lines to the DM
PWB via the TS connector and then to the Xilleon
microprocessor.
(Example of VBI period - Pin 43 of IC2K01)
(Figure 1)
1/2 Frame
1/2 Frame
VBI
Total VBI Period
1 0
1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1
Line 10
starts
possible data
Example
data
(Example of VBI data - Pin 1 of IC7R01)
(Figure 2)
If there is no data in the VBI
then either you are not tuned
to a host channel that
broadcasts the data, there is
currently no data being
broadcast, or there is an
upstream problem with the
tuner circuit.
TIP:
A test tape can be created by
recording the channel with the
TVGuide VBI data onto a VHS tape.
The recording must be during the
time that the data is transmitted. It
can be used for the VBI slicing test
on the next page.
TS
Main Tuner (TU-100)
(Cable/ATSC/NTSC)
IC7R04
MULTIPLEXER
IC2K01
VIDEO SWITCH
IC7R05
SYNC
SEPARATOR
IC7R01
PIC
MICRO
SIGNAL-PWB
DM-PWB
Air
in
Cable
Matrix SW
IC7R02
COMPARATOR
18
61
43
6
15
3
2
7
1
7
6
9
10
7
8
17
8
IC8307
QUAD
UART
9
10
24
25
27
26
51
41
TU
1
-C
V
G+VID
(SUB-Y)
V-SYNC
H-SYNC
VBI-DATA-IN
GOS-TXD
GOS-RXD
XILLEON
SWITCH
CONTROL
4
SYNC-PLL
2
1
3
Содержание LT-37131
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Страница 4: ...MODELS LT 37131 LT 37132 LT 46131 LT 46231 Page 4 ...
Страница 37: ...Page 37 MODELS LT 37131 LT 37132 LT 46131 LT 46231 POWER SUPPLY ...
Страница 38: ...Page 38 MODELS LT 37131 LT 37132 LT 46131 LT 46231 DM SIGNAL POWER SUPPLIES ...
Страница 39: ...Page 39 MODELS LT 37131 LT 37132 LT 46131 LT 46231 VIDEO SIGNAL PATH ...
Страница 40: ...Page 40 MODELS LT 37131 LT 37132 LT 46131 LT 46231 AUDIO SIGNAL PATH ...
