sta015t STMicroelectronics, sta015t Datasheet - Page 9

• Manufacturer Part Number: sta015t
• Description: Mpeg 2.5 Layer Iii Audio Decoder With Adpcm Capability
• Manufacturer: STMicroelectronics

2.5 - STA015 Operation Mode
The STA015 can work in two different modes,
called Multimedia Mode and Broadcast Mode.
In Multimedia Mode (default mode) STA015 de-
codes the incoming bitstream, acting as a master
of the data communication from the source to it-
self.
This control is done by a specific buffer manage-
ment, controlled by STA015 embedded software.
The data source, by monitoring the DATA_REQ
line, send to STA015 the input data, when the
signal is high (default configuration).
The
DATA_REQ line is low.
In this mode the fractional part of the PLL is dis-
abled and the audio clocks are generated at
nominal rates. Fig. 7 describes the default
DATA_REQ signal
STA015 it is possible to invert the polarity of the
DATA_REQ line (register REQ_POL).
Figure 7.
In Broadcast Mode, STA015 works receiving a
bitstream with the input speed regulated by the
source. In this configuration the source has to
guarantee that the bitrate is equivalent to the
nominal bitrate of the decoded stream.
To compensate the difference between the nomi-
nal and the real sampling rates, the STA015 em-
bedded software controls the fractional PLL op-
eration. Portable or Mobile applications need
SOURCE STOPS TRANSMITTING DATA
DATA_REQ
communication is
SOURCE SEND DATA TO STA015
behaviour. Programming
stopped when the
SOURCE STOPS TRANSMITTING DATA
D00AU1144
normally to operate in Broadcast Mode. In both
modes the MPEG Synchronisation is automatic
and transparent to the user.
2.6 - STA015 Decoding States
There are three different decoder states: Idle,
Init, and Decode. Commands to change the de-
coding states are described in the STA015 I
registers description.
Idle Mode
In this mode the decoder is waiting for the RUN
command. This mode should be used to initialise
the configuration registers of the device. The
DAC connected to STA015 can be initialised dur-
ing this mode (set MUTE to 1).
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
PLAY
0
0
1
1
X
X
MUTE
0
1
0
1
MUTE
STA015-STA015B-STA015T
0
1
Not Running
Clock State
Running
Running
Running
Not Running
Clock State
Running
Decoded
Samples
Output
PCM
0
0
0
PCM Output
Decoding
0
0
Yes
Yes
No
No
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