HMP8117 Datasheet, PDF (19/45 Pages) Intersil Corporation – NTSC/PAL Video Decoder

HMP8117
DETECTION OF TELETEXT
The teletext decoder monitors the scan lines, looking for the
16-bit clock run-in (sometimes referred to as the clock
synchronization code) used by teletext. If found, it locks to
the clock run-in, the teletext data is sampled and loaded into
shift registers, and the data is then transferred to internal
holding registers.
If the clock run-in is not found, it is assumed the scan line
contains video data unless other VBI information is detected,
such as WSS.
If a teletext clock run-in is found before line 23 or line 289 for
NTSC and (M) PAL, or line 336 for (B, D, G, H, I, N, N_C) PAL,
the VBI Teletext Detect status bit is immediately set to “1”. If not
found by these lines, the status bit is immediately reset to “0”.
CLOCK
RUN-IN
ACCESSING THE TELETEXT DATA
The teletext data must be output as BT.656 ancillary data.
The I²C interface does not have the bandwidth to output
teletext information when needed.
Table 8 illustrates the teletext BT.656 ancillary data format
and Figure 15 depicts the portion of the incoming teletext
signal which is sliced and output as part of the ancillary data
stream. The teletext data is present during the horizontal
blanking interval after the line containing the teletext
information. The actual BT.656 bytes that contain teletext
data only contain 4 bits of the actual data packet. Note that
only the data packet of Figure 16 is sent as ancillary data;
the clock run-in is not included in the data stream.
DATA PACKET
Bit 0
MSB
NOTES:
30. The MSB is bit number: 271 for system C, 279 for system B 525-line and 343 for system B 625-line.
31. The clock run-in is 16 bits wide for both systems and is not included in the BT.656 ancillary data stream.
32. The bit rate is 5.727272 Mbits/s for system B and C on 525/60 systems and 6.9375 and 5.734375 Mbits/second respectively for 625/50 systems.
33. Teletext VBI Video Signal
FIGURE 16. TELETEXT VBI VIDEO SIGNAL
TABLE 8. OUTPUTTING THE SLICED TELETEXT DATA AS BT.656 ANCILLARY DATA
PIXEL INPUT
P15
P14
P13
P12
P11
P10
P9
P8
Preamble
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Data ID
P14
ep
1
1
0
1
0
0
Data Block Number
P14
ep
0
0
0
0
0
1
Data Word Count
P14
ep
0
1
0
1
1
0
Teletext Data
P14
ep
0 = 525-line
0 = system B
bit 343 bit 342 bit 341 bit 340
(B, 625-line = 43 bytes)
1 = 625-line
1 = system C
(B, 525-line = 35 bytes)
(C = 34 bytes)
P14
ep
0
0
bit 339 bit 338 bit 337 bit 336
:
P14
ep
0
0
bit 7
bit 6
bit 5
bit 4
P14
ep
0
0
bit 3
bit 2
bit 1
bit 0
Reserved
P14
ep
0
0
0
0
0
0
P14
ep
0
0
0
0
0
0
CRC
P14
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
NOTES:
34. ep = even parity for P8-P13.
35. CRC = Sum of P8-P14 of Data ID through last user data word. Preset to all zeros, carry is ignored.
36. For 525-line system B, bits 280-343 are “0”.
37. For system C, bits 272-343 are “0”.
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