SAA7205 Philips Semiconductors, SAA7205 Datasheet - Page 13

• Manufacturer Part Number: SAA7205
• Description: MPEG-2 systems demultiplexer
• Manufacturer: Philips Semiconductors

Philips Semiconductors
7.2
The demultiplexer receives data from a Forward Error
Correction (FEC) decoder (see Fig.4) or a descrambler
(see Fig.5) in a digital TV receiver in the following input
data format:
The parser module in the demultiplexer parses MPEG-2
systems compliant transport streams. MPEG-2 systems
specifies a hierarchical two level multiplex (see Fig.6).
The top hierarchical level is the transport stream,
consisting of relatively short (188 byte) transport packets.
Each transport packet consists of a 4 byte transport
header, an optional adaptation field and a payload.
1997 Jan 21
A number of data bits via PKTDAT7 to PKTDAT0
(8-bit wide input bus)
A valid input data indicator signal (PKTDATV) which is
HIGH for consecutive valid bytes and output by either a
FEC decoder or a descrambler. The demultiplexer input
is allowed to have a ‘bursty’ nature.
A transport packet error indicator (PKTBAD/PKTBAD)
which is HIGH for the duration of each 188 byte
transport packet in which the FEC decoder found more
errors than it could correct. The polarity (active HIGH or
LOW) of the error indicator is programmable
(bit Bad_polarity, address 0x0100; see Table 13).
A packet sync signal (PKTSYNC) which goes HIGH at
the start of the first byte of a transport packet. Only the
rising edge of PKTSYNC is used for synchronization,
the exact HIGH time of the signal is therefore irrelevant.
A byte strobe signal [PKTBCLK (< 9 MHz)] which
indicates consecutive data bytes in the input stream, in
the non-9 MHz mode only (bit 9 MHz_interface = 0,
address 0x0100;see Table 13). PKTBCLK is used as an
enable signal and transport stream input bytes are
sampled on its rising edges of the clock pulse. If the
input interface is programmed to the 9 MHz mode
(9 MHz interface = 1), the PKTBCLK signal is ignored.
A descrambler clock signal [DCLK (9 MHz, 30% duty
cycle)] which is the data output clock for the
descrambler. If rising edges of this clock signal are used
to input data to the demultiplexer the 9 MHz mode must
be used (bit 9 MHz_interface = 1, address 0x0100;
see Table 13).
MPEG-2 systems demultiplexer
MPEG-2 systems parsing
13
The transport header contains a 13-bit packet
identification field. The adaptation field may contain
Program Clock Reference (PCR) data and transport
private data, among others. Both the transport header and
the optional adaptation fields are parsed by the parser
module within the demultiplexer. The individual states of
the MPEG-2 parser in the demultiplexer are listed in
Table 14.
The hierarchical multiplex level below the MPEG-2
transport stream and the packetized elementary stream, is
partly parsed by the demultiplexer, for instance in the
audio and video filters. A packetized elementary stream
consists of an elementary stream (e.g. MPEG-2 audio, or
video data) which is divided into subsequent variable
section lengths. To each section a PES header is added,
thus creating PES packets. A PES header may contain
time stamp information (PTS or DTS), scrambling control,
copy information and PES private data.
In the demultiplexer, parsing is performed for all incoming
transport packets. The parser is synchronized to a rising
edge on the PKTSYNC input. A microcontroller can
compose a set of PIDs by programming the appropriate
registers in the various filters within the demultiplexer. If a
packet is part of an audio or video transport stream, some
of the information fields in the transport and PES packet
headers are automatically retrieved. The microcontroller
can read the obtained information. Table 2 lists data that
can be accessed by the microcontroller, for both video
(address 0x0509; see Table 13) and audio streams
(address 0x0609; see Table 13).
MPEG-2 multiplex fields which are related to program
specific information (PSI), service information (SI), private
data and conditional access data (called sections) are
parsed partly in the section data filters. Program
association tables, program map tables and conditional
access tables can be retrieved from the stream and stored
in buffers in an external 32K
performed (optional) for transport_private_data,
PES_private_data, and private sections in the subtitling
and section data filters. A microcontroller may access data
in the section data and subtitling buffers for further
processing in software.
8 SRAM. The same can be
Preliminary specification
SAA7205H