SAA2520 Datasheet, PDF(17/36 Page) NXP Semiconductors – Stereo filter and codec for MPEG layer 1 audio applications

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SAA2520 Datasheet, PDF (17/36 Pages) NXP Semiconductors – Stereo filter and codec for MPEG layer 1 audio applications

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Philips Semiconductors

Stereo ï¬lter and codec for MPEG layer 1

audio applications

Preliminary speciï¬cation

SAA2520

MPEG Coded Interface (Sub-band I2S)

The MPEG coded data is transferred to and from the

SAA2520 using the format shown in Fig.14.

Each period of SBWS contains 64 data bits, 32 of which

are used to convey data. The half-period during which

SBWS is logic 0 is used to transfer the first 16-bits (0 to 15)

of a sub-band slot. The remaining half-period during which

SBWS is logic 1 carries the remaining 16-bits (16 to 31).

Thus one period of SBWS corresponds with one slot of the

sub-band signal.

Bits 0 and 16 are transferred in the bit clock period, one

bit-time after the change in SBWS. Both SBWS and SBDA

change state during the negative edge of SBCL.

In decode mode a byte error flag SBEF is also transferred.

This occurs approximately in the middle of the

corresponding byte (byte 0 = bits 0 to 7,

byte 1 = bits 8 to 15 etc).

Encoding mode

SBCL, SBWS and SBDA are generated by the SAA2520.

However, if the SBDIR signal is logic 1, the output buffers

are not enabled and these signals do not appear on the

pins. This mode is available to permit a change of

operating mode whilst the bus signals are driven from an

external source.

Decoding mode

SBCL, SBWS and SBDA are generated by an external

source.

Table 3 contains a summary of the source signals in the

various modes.

Table 3 Modes and source signals.

source of:

Mode

Encode

Decode

FDIR

SBDIR

SBWS

INT

EXT

INT

EXT

SBCL

INT

EXT

INT

EXT

SBDA

INT

EXT

INT

EXT

SBEF

----

EXT

SBMCLK

INT

note 1

note 2

note 3

Notes

1. During encoding the SBEF signal is âdonât careâ.

2. Incoming data is not decoded. The SAA2520 operates in the encoding mode and the data does not enter the

interface.

3. Operation is undefined. The SAA2520 is in decoding mode whilst the SBWS, SBCL and SBDA output drivers are

enabled.

August 1993

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