Table 77: Number Of Bits In Each Of Framing Codes; Table 78: Number Of Data Words In Ancillary Data Packet For Some Vbi Standards - Analog Devices ADV7850 Hardware Manual

User Data Word N-1
Padding
Padding
Checksum
Ancillary packet data is composed of the following:
• Ancillary Data Preamble: First 3 bytes are the ancillary data preamble which indicates the start of a data packet. It will always be
0x00, 0xFF, 0xFF. The FF is a condition that cannot exist outside the preamble and the user data words. This is because D7 and
D6 are an exclusive OR pair, in that when one is high, the other must be low. D6 is generally chosen to be an even parity bit,
which is high if the number of 1's in D5:D0 is odd and low if the number of 1's in D5:D0 is even. D7 is then always NOT D6,
ensuring that the all one and all zero condition cannot occur.
• Data ID (DID): Indicates the type of data being sent.
Secondary DID (SDID): Supplements the data ID for type 2 ancillary formats.
•
Data Count (DC): Indicates that number of user data words in the packet.
•
LCount: Advises the line from which this particular data packet was extracted.
•
• Even Field (EF): Indicates the field from which the packet was decoded.
• Checksum: Word used to increase the confidence in the integrity of the ancillary data packet. It is calculated by summing the 7
LSBs of all bytes from Data ID to User Data Word N-1. The 7 LSBs of this summation is the checksum, with the MSB being the
NOT of the D6.
VBI Data Standard: VBI data standard that should be decoded on each line of an incoming video is set by default. This can be
•
over-ridden manually and any VBI data can be decoded from any line. Four bits are used in the ancillary packet to indicate
which type of VBI data is encoded in the packet. (Refer to
The first three VBI words are the framing codes (total of 24 bits). Some of the values used are shown in
each of the standards, but the framing codes for these standards may be less. Hence, the No. of Bits column indicates how many bits are
used by the framing code for that standard in practice.
VBI Standard
CCAP (525i & 625i)
WSS (625i)
CGMS-A (525i, 525p, 720p, 1080i)
CGMS-B
Teletext System A
Teletext System B
Teletext System C
Teletext System D
VPS
VITC
GEMSTAR_1X
GEMSTAR_2X:
These are then followed by the VBI data. The typical numbers of user data words are shown in
Standard
CCAP
WSS
CGMS-A
CGMS-B
Rev. A May 2012

Table 77: Number of Bits in Each of Framing Codes

Table 78: Number of Data Words in Ancillary Data Packet for Some VBI Standards

No. of User data No. of Framing
Words Codes
4 3
4 3
4 3
4 3
D7 D6 D5 D4
VBI Word N-1[7:0]
1 0 0 0
����
��6
1 0 0 0
Checksum
Table 62 for details.)
Framing Code
0x80, 0x00, 0x00
0xF8, 0x3C, 0x78
0x00, 0x00, 0x00
0x00, 0x00, 0x00
0xE7, 0x00, 0x00
0x27, 0x00, 0x00
0x27, 0x00, 0x00
0xE7, 0x00, 0x00
0x99, 0x51, 0x00
0x00, 0x00, 0x00
0x80, 0x00, 0x00
0xB7, 0x20, 0x00
No. of VBI Data
Words
2
2
3
17
325
D3 D2 D1 D0
0 0 0 0
0 0 0 0
Table 77. Three bytes are used for
No. of Bits
3
24
8
8
8
8
16
1
3
1
Table 78.
No. of Padding
Words Sum
3 12
3 12
2 12
0 24
ADV7850