Sync 1 Inversion And Scrambler/Descrambler; Figure A-15. Scrambler/Descrambler - Comtech EF Data SDM-9000 Installation And Operation Manual

SDM-9000 Satellite Modem
A.2.6 SYNC 1 Inversion and Scrambler/Descrambler
In compliance with the DVB specifications, and to ensure adequate binary transitions,
the payload data (187 bytes) in the transport packet is scrambled using a Pseudo Random
Binary Sequence (PRBS) generator.
The polynomial used for the PRBS is:
1 + X
The basic scrambler/descrambler is shown in Figure A-15.
ENABLE FROM
SYNC DETECT LOGIC
At every eighth transport packet, the sequence "100101010000000" is loaded into the
PRBS registers. The inverted sync byte is used to initialize the PRBS generator.
Rev. 4
14 15
+ X
INITIALIZATION SEQUENCE
1 0 0 1 0 1
1 2 3 4 5 6
CLEAR/SCRAMBLED
DATA IN

Figure A-15. Scrambler/Descrambler

0 1 0 0 0 0
7 8 9 10 11 12 13 14 15
PRBS GENERATOR
0 0 0
SCRAMBLED/
DESCRAMBLED
DATA OUT
Options
A–19