ADV7180
Gemstar Bit Names
•
•
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 may be required
at the end, as set in ITU-R BT.1364. See Table 83.
•
DID—The data identification value is 0x140 (10-bit value).
Care has been taken so that in 8-bit systems, the two LSBs
do not carry vital information.
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, the 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 2 LSBs set to 0, the
CS[1:0] bits are also always 0.
EP
•
EP and —The EP bit is set to ensure even parity on
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.
and is output on D[9]. The
reserved codes of 00 and FF do not occur.
EP
describes the logic inverse of EP
EP
is output to ensure that the
•
•
EF—Even field identifier. EF = 1 indicates that the data was
recovered from a video line on an even field.
CS
CS
[8]—describes the logic inversion of CS[8]. The value [8]
is included in the checksum entry of the data packet to ensure
that the reserved values of 0x00 and 0xFF do not occur.
2×—This bit indicates whether the data sliced was in
Gemstar 1× or 2× format. A high indicates 2× format.
The 2× bit determines whether the raw information
retrieved from the video line was two bytes 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.
Table 84 to Table 89 outline the possible data packages.
Gemstar_2× Format, Half-Byte Output Mode
Half-byte output mode is selected by setting CDECAD to 0;
full-byte output mode is selected by setting CDECAD to 1. See
the GDECAD, Gemstar Decode Ancillary Data Format,
Address 0x4C [0] section.
Gemstar_1× Format
•
line[3:0]—This entry provides a code that is unique for
each of the possible 16 source lines of video from which
Gemstar data may have been retrieved. Refer to Table 92
and Table 93.
Half-byte output mode is selected by setting CDECAD to 0,
full-byte output mode is selected by setting CDECAD to 1. See
the GDECAD, Gemstar Decode Ancillary Data Format,
Address 0x4C [0] section.
Table 84. Gemstar_2× Data, Half-Byte Mode
Byte
D[9]
D[8]
D[7]
D[6]
D[5]
D[4]
D[3]
D[2]
D[1]
D[0]
Description
Fixed preamble
Fixed preamble
Fixed preamble
DID
0
0
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
0
1
1
1
1
1
1
1
2
1
1
1
1
1
1
3
0
1
0
1
0
0
4
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
CS[8]
EP
EP
EP
EP
EP
EP
EP
EP
EP
EP
CS[8]
EF
0
1
0
0
SDID
line[3:0]
5
0
0
0
1
0
0
0
Data count
6
0
0
0
0
Gemstar word1[7:4]
Gemstar word1[3:0]
Gemstar word2[7:4]
Gemstar word2[3:0]
Gemstar word3[7:4]
Gemstar word3[3:0]
Gemstar word4[7:4]
Gemstar word4[3:0]
User data-words
User data-words
User data-words
User data-words
User data-words
User data-words
User data-words
User data-words
Checksum
7
0
0
0
0
8
0
0
0
0
9
0
0
0
0
10
11
12
13
14
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
CS[7]
CS[6]
CS[5]
CS[4]
CS[3]
CS[2]
CS[1]
CS[0]
Rev. A | Page 66 of 112
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