SAA7206 データシートの表示（PDF） - Philips Electronics

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SAA7206

DVB compliant descrambler

Philips Electronics 

Philips Semiconductors

DVB compliant descrambler

Product specification

SAA7206H

7 FUNCTIONAL DESCRIPTION

A block diagram of the internal structure of the

descrambler (DVB compliant) is illustrated in Fig.1.

The block diagram illustrates the main functional modules

in the descrambler. The modules are as follows:

• The MPEG-2 syntax parser, which parses transport

streams that comply with the MPEG-2 systems

specification

• The descrambler module consisting of:

– A Packet Identification (PID) bank containing 6 PID

values of the streams selected for descrambling.

All bits of PID5 (address 0x0205) can be masked

individually with PID5_mask (address 0x0209), to

enable multiple PID selection.

– A Control Word (CW) bank containing 6 CW pairs

and a default CW. A CW pair consists of

2 descrambler control words (odd and even), each

word with a length of 64 bits.

– The descrambler core containing the actual

descrambler with the stream cipher and the block

cipher module.

• A microcontroller interface providing protocol handling

for the memory mapped I/O control bus

(Philips 90CE201 compatible). This module contains an

interrupt request handler and data filters for the retrieval

of Conditional Access (CA) information:

• The CA filters select data on the basis of PIDs, and a

combination of MPEG-2 section addressing fields.

Selected CA data is stored in eighteen 256 byte

(constrained random access) buffers which can be read

by the microcontroller. The CA message section has a

maximum length of 256 bytes. It consists of a 3 bytes

long header with Table_id and section_length data.

The remaining part of the CA message are the

CA_data_bytes (see Fig.4). If a section is longer than

256 bytes, the data capture is stopped (with an interrupt

to the microcontroller) after 256 bytes are in the buffer

and the ‘section_to_long’ bit is set. The filters are

capable of monitoring 18 CA streams (containing EMM

and ECM data) simultaneously. Two different lengths

are used for address filtering:

– 16 filters where the first 7 bytes of the CA_data_bytes

field are used for address filtering

– 2 (DVB compliant) filters where the first 17 bytes of

the CA_data_bytes field are used for address filtering

– A chip identification byte (value 0x02) can be read by

the software from address 0x0003 (see Table 10).

handbook, full pagewidth

CONDITIONAL

ACCESS

SYSTEM

MICRO-

CONTROLLER

DEMODULATOR

AND

FORWARD ERROR

CORRECTOR

DVB

DESCRAMBLER

(SAA7206H)

DEMULTIPLEXER

(SAA7205)

MGG314

1996 Oct 09

Fig.3 Demultiplexer system configuration.

8

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