ADV7184_15 Datasheet, PDF (71/112 Pages) Analog Devices – Multiformat SDTV Video Decoder with Fast Switch Overlay Support

Table 85. Data Byte Allocation
Raw Information Bytes
Gemstar 2× Retrieved from the Video Line
1
4
1
4
0
2
0
2
ADV7184
GDECAD
0
1
0
1
User Data-Words
(Including Padding)
8
4
4
4
Padding Bytes
0
0
0
2
DC [1:0]
10
01
01
01
Gemstar Bit Names
• DID. The data identification value is 0x140 (10-bit value).
Care has been taken that in 8-bit systems, the two LSBs do
not carry vital information.
• EP and EP. The EP bit is set to ensure even parity on the
data-word D [8:0]. Even parity means there is always an
even number of 1s within the D [8:0] bit arrangement. This
includes the EP bit. EP describes the logic inverse of EP
and is output on D [9]. The EP is output to ensure that the
reserved codes of 00 and FF cannot occur.
• EF. Even field identifier. EF = 1 indicates that the data was
recovered from a video line on an even field.
• 2×. This bit indicates whether the data sliced was in
Gemstar 1× or 2× format. A high indicates Gemstar 2×
format. The 2× bit determines whether the raw information
retrieved from the video line was two or four bytes. The
state of the GDECAD bit affects whether the bytes are
transmitted straight (that is, two bytes transmitted as two
bytes) or whether they are split into nibbles (that is, two
bytes transmitted as four half bytes). Padding bytes are
then added where necessary.
• line [3:0]. This entry provides a code that is unique for
each of the 16 possible source lines of video from which
Gemstar data may have been retrieved. Refer to Table 94
and Table 95.
• DC [1:0]. Data count value. The number of UDWs in the
packet divided by 4. The number of UDWs in any packet
must be an integral number of 4. Padding is required at the
end, if necessary, as set in ITU-R BT.1364. See Table 85.
• CS [8:2]. The checksum is provided to determine the
integrity of the ancillary data packet. It is calculated by
summing up D [8:2] of DID, SDID, data count byte, and all
UDWs, and ignoring any overflow during the summation.
Because all data bytes that are used to calculate the checksum
have their two LSBs set to 0, the CS [1:0] bits are also always 0.
CS[8] describes the logic inversion of CS [8]. The value
CS[8] is included in the checksum entry of the data packet
to ensure that the reserved values of 0x00 and 0xFF do not
occur. Table 86 to Table 91 outline the possible data packages.
Gemstar 2× Format, Half-Byte Output Mode
Half-byte output mode is selected by setting GDECAD to 0;
full-byte output mode is selected by setting GDECAD to 1.
See the GDECAD, Gemstar Decode Ancillary Data Format,
Address 0x4C [0] section.
Gemstar 1× Format, Half-Byte Output Mode
Half-byte output mode is selected by setting GDECAD to 0;
full-byte output mode is selected by setting GDECAD to 1.
See the GDECAD, Gemstar Decode Ancillary Data Format,
Address 0x4C [0] section.
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