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STA003T

MPEG 2.5 LAYER III AUDIO DECODER

STMicroelectronics 

STA003T

2.4 - PCM Output Interface

The decoded audio data are output in serial PCM

format. The interface consists of the following sig-

nals:

SDO

PCM Serial Data Output

SCKT

PCM Serial Clock Output

LRCLK Left/Right Channel Selection Clock

The output samples precision is selectable from

Figure 8. PCM Output Formats

16 to 24 bits/word, by setting the output precision

(16, 18, 20 and 24 bits) with PCMCONF register.

Data can be output either with the most signifi-

cant bit first (MS) or least significant bit first (LS),

selected by writing into a flag of the PCMCONF

register.

Figure 8 gives a description of the STA003T PCM

Output Formats.

The sample rates set decoded by STA003T is de-

scribed in Table 1.

LRCKT

16 SCLK Cycles

16 SCLK Cycles

16 SCLK Cycles

16 SCLK Cycles

16 SCLK Cycles

M

SDO

S

SDO

L

S

LM

SS

ML

SS

LM

SS

ML

SS

LM

SS

ML

SS

L PCM_ORD = 0

S PCM_PREC is 16 bit mode

M PCM_ORD = 1

S PCM_PREC is 16 bit mode

LRCKT

SDO

SDO

SDO

SDO

32 SCLK Cycles

32 SCLK Cycles

32 SCLK Cycles

32 SCLK Cycles

32 SCLK Cycles

M

S

L

S

0

M

S

L

S

0

M

S

L0

S

M

S

L0

S

PCM_FORMAT = 1

PCM_DIFF = 1

0M

S

L

S

0

M

S

L

S

0

M

S

L

S

0

M

S

L PCM_FORMAT = 0

S PCM_DIFF = 0

0M

S

L 0 0M

S

S

L

S

0

0M

S

L

S

0

0M

S

L

S

0

PCM_FORMAT = 0

PCM_DIFF = 1

MSB

M

S

L

S

MSB

M

S

L

S

M

MSB S

L

S

MSB

M

S

L PCM_FORMAT = 1

S PCM_DIFF = 1

Table 1: MPEG Sampling Rates (KHz)

MPEG 1

48

32

MPEG 2

24

16

MPEG 2.5

12

8

2.5 - STA003T Decoding States

There are three different decoder states: Idle,

Init, and Decode. Commands to change the de-

coding states are described in the STA003T I2C

registers description.

Idle Mode

In this mode the decoder is waiting for the RUN

command. This mode should be used to initialise

the configuration register of the device. The DAC

connected to STA003T can be initialised during

this mode (set MUTE to 1).

PLAY

X

X

MUTE

0

1

Clock State PCM Output

Not Running

0

Running

0

Init Mode

"PLAY" and "MUTE" changes are ignored in this

mode. The internal state of the decoder will be

updated only when the decoder changes from the

state "init" to the state "decode". The "init" phase

ends when the first decoded samples are at the

output stage of the device.

Decode Mode

This mode is completely described by the follow-

ing table:

PLAY

0

0

1

1

MUTE

0

1

0

1

Clock State

PCM

Output

Decoding

Not Running 0

No

Running

0

No

Running Decoded Yes

Samples

Running

0

Yes

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