2.6.1 Sync Insertion Mode
The Sync/EF unit inserts new sync words if that mode is programmed
(see Section 4.1.2, “Register 1,” page 4-4). Sync insertion can be useful
to work against bit errors in sync bytes, even if sync is already inserted
in the stream. If the bitstream contains sync bytes that the device uses
for synchronization, the regenerated sync bytes conceal single errors in
the synchronization pattern.
In unsynchronized states S0, S1, and S2, the L64777 bypasses data bits
without any modification of the sync byte. After it establishes
synchronization (in states S3, S4 and S5), the device inserts the
regenerated sync pattern based on the programming of Register 1.
2.6.2 Error Flag Insertion
The next processing task is the error flag handling for MPEG-2 transport
packets. If ERRORIN indicates a decoder error at the first byte of a
frame, the L64777 sets the TRANSPORT_ERROR_INDICATOR bit of
the MPEG-2 packet. This is the MSB of the second byte in a packet (see
Figure 2.10). If there is no error indication, the L64777 passes the
TRANSPORT_ERROR_INDICATOR bit transparently.
Figure 2.10 Transport Error Flag Insertion
Errorin
...don’t care on /Error...
FstartIn
Din[0]
7
6 5 4 3 2 1 0
SYNC_BYTE (0x47)
Start of transport packet
2.6.3 Energy Dispersal (Scrambler) Unit
The function of the Scrambler is specified for the serial domain by the
Digital Broadcasting Systems for Television Sound and Data Services:
Framing Structure, Channel Coding and Modulation Cable Systems. The
energy dispersal module (scrambler) operates in Parallel mode based on
the algorithm of the serial domain. Figure 2.11 illustrates the basic serial
architecture of the Scrambler.
2-18
Modulator Architecture
ETC [ ETC ]
