SAA7205 Philips Semiconductors, SAA7205 Datasheet - Page 44

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

Philips Semiconductors
7.14.2
The long filter module is capable of accessing, for
instance, electronic program guides or event information
tables, transported in private sections, with a length of up
to and including 4 kBytes. The configuration of the long
filter module is shown in Fig. 27.
The filter consists of 4 section detectors. Each section
detector selects and retrieves section data on the basis of:
The section data detected by a certain section detector is
always stored in the associated 4 kByte section buffer.
As soon as an entire section of data is stored, an interrupt
(interrupt: ‘fltC_F_irpt’, address 0x0000, see Table 13) is
generated. The 4 section detectors can be separately
enabled (disabled), to avoid unnecessary interrupts.
The ‘filter fired’ registers enable the microcontroller to track
which section detector loaded its buffer (bits ‘flt
[F to C]_frd’, address 0x0304, see Table 13). Each of the
section detectors checks incoming data for errors by
means of the CRC_32 mechanism specified in MPEG2
systems. If an error is detected, an error status flag is set
(bit ‘err_stat’, see Table 13) in the filter unit. The error flag
can therefore be accessed by the microcontroller.
If the microcontroller decides to read data from the long
filter buffers (see Table 13; address range as indicated in
Table 10) it can determine when to stop reading in two
ways. It can periodically poll the ‘flt [F to C]_stat’ bits in the
interrupt status register (address 0x0003, see Table 13).
These bits go LOW as soon as the last valid section data
word is read from the section buffer.
Another possibility is for the microcontroller to read the
‘high_address’ word (‘hadr [9 to 0]’, see Table 13). This
word is proportional to the number of valid section words
(1 word equals 2 bytes) that was written into the buffer.
Actually #words equal ‘high_address’ + 1. This number
equals the number of read cycles that has to be performed
to retrieve all valid data from the buffer.
If the buffer contents have to be removed without being
read, the microcontroller can write a logic 1 to the ‘rst_bf
[F to C]’ bit (address 0x0315, see Table 13) thus releasing
the buffer. Another possibility is to perform one write
address operation to (0x.... - hadr [9 to 0] + 1). The internal
auto-increment address counter is thus set to the last byte
in the buffer and the filters are reactivated, after having
been idle during buffer emptying.
1997 Jan 21
PID
Table_id
7 maskable bytes (56 bits) in the section payload
(see Fig. 27).
MPEG-2 systems demultiplexer
L
ONG FILTER MODULE
44
7.14.3
The subtitling filter is capable of accessing, for instance,
subtitling data transported in PES packets, transport
packet private data or PES private data. The architecture
of the subtitling filter is shown in Figs 27 and 28.
The filter consists of 1 PES detector, which selects and
retrieves data on the basis of PID filtering. The subtitling
data (including PES header), or private data (without
headers) detected by the filter is stored in a 4 kByte PES
FIFO.
The microcontroller can read the data in the FIFO one
word (equals 2 bytes) at a time. The ‘subt_cont’ (address
0x0303, see Table 13) register indicates the number of
bytes in the FIFO. If this number is odd, one byte remains
after reading all words. Before reading the last byte the
‘hlt_adr_ptr’ bit has to be set (address 0x0301,
see Table 13). The valid byte can be found in the MSB’s.
The first byte of new data is stored in the LSB. Reset the
‘hlt_adr_ptr’ before reading the new data.
An interrupt ‘subt_irpt’ (address 0x0000, see Table 13) is
generated as soon as the FIFO contains more than a
programmable level of bytes. This level may indicate that
there is just enough room in the FIFO to store one
additional packet payload. The microcontroller should
therefore start reading data, or halt data retrieval
(‘enable’ = 0, address 0x0300, see Table 13) otherwise an
overflow may occur.
The subtitling filter is capable of retrieving private data on
the basis of PID selection (word: ‘subt_pid’, address
0x0300, see Table 13) by programming ‘priv_dat’ to
logic 1 (address 0x0301, see Table 13). The filter can be
programmed to retrieve transport_private_data (bit:
‘pes_afn’ = 0, address 0x0301, see Table 13) or
PES_private_data (‘pes_afn’ = 1) for a selected PID.
The filter is separately enabled (bit ‘enable’, address
0x0300, see Table 13).
S
UBTITLING FILTER
Preliminary specification
SAA7205H