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CPP100
SECTION 6
CPP1OPS
25/10/06
www.snellwilcox.com
Version 1 Issue 6
6.20
DBLK: Data Block Number
The data block number is incremented by 1 for each consecutive data packet sharing a
common DID and requiring continuity indication. This is always set to zero in Prefix.
DCN\\\\SNELLWILCOX.LOCAL\\ROOT\\MARKETING\\PRODMGMT\\DATA
Data Count
This byte represents the number of user data words to follow, and in this case it is always
set to 16.
C/SUM: Check Sum
The checksum word is used to determine the validity of the Ancillary Data Packet from the
DID through the user defined words (UDWs). The checksum value is equal to the nine
least significant bits of the sum of the DID, the DBLK the DCNT and all UDWs in the packet.
In 8-bit applications, where the two LSBs of every 10-bit word in the packet are set to zeros,
the C/SUM word is calculated in the same way as for 10-bit applications. (The LSBs
produce a zero sum themselves and produce no carry bit).
User data words: (UDW)
All user defined words can be described as bitwise utilising bits 2 through 7 with bit 8
defined as parity and bit9 set to “NOT bit 8”.
To ensure that no data is lost through 8 bit equipment, bits 1 & 0 are not used
Positioning
The flag information is inserted on the following lines: -
HANC
625 line Standard
525 line Standard
Field 1
6
10
Field 2
319
273
NOTE - although it is recommended that Ancillary Data Packets are not transmitted within
the ancillary space on line 10/273 or line 6/319 (as switching may occur during these lines),
receiving equipment should process ancillary data located in any ancillary data space.
Synchronous switching of picture sources will invalidate the analysis information in any
case; therefore it is convenient to locate the data on the switching lines for the configuration
where Prefix analysis data is used with a compression encoder.
Additionally, these lines have been chosen because they are guaranteed to be free from
embedded audio packets, which are not permitted on the switching lines.