AT83SND1CXXX-ROTIL datasheet(63/212 Pages) ATMEL

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4109J–8051–10/06

AT8xC51SND1C

12. MP3 Decoder

The AT8xC51SND1C implement a MPEG I/II audio layer 3 decoder better known as MP3

decoder.

In MPEG I (ISO 11172-3) three layers of compression have been standardized supporting three

sampling frequencies: 48, 44.1, and 32 kHz. Among these layers, layer 3 allows highest com-

pression rate of about 12:1 while still maintaining CD audio quality. For example, 3 minutes of

CD audio (16-bit PCM, 44.1 kHz) data, which needs about 32M bytes of storage, can be

encoded into only 2.7M bytes of MPEG I audio layer 3 data.

In MPEG II (ISO 13818-3), three additional sampling frequencies: 24, 22.05, and 16 kHz are

supported for low bit rates applications.

The AT8xC51SND1C can decode in real-time the MPEG I audio layer 3 encoded data into a

PCM audio data, and also supports MPEG II audio layer 3 additional frequencies.

Additional features are supported by the AT8xC51SND1C MP3 decoder such as volume control,

bass, medium, and treble controls, bass boost effect and ancillary data extraction.

12.1

Decoder

12.1.1

Description

The C51 core interfaces to the MP3 decoder through nine special function registers: MP3CON,

the MP3 Control register (see Table 62); MP3STA, the MP3 Status register (see Table 63);

MP3DAT, the MP3 Data register (see Table 64); MP3ANC, the Ancillary Data register (see

Table 66); MP3VOL and MP3VOR, the MP3 Volume Left and Right Control registers (see

Table 67 and Table 68); MP3BAS, MP3MED, and MP3TRE, the MP3 Bass, Medium, and Treble

Control registers (see Table 69, Table 70, and Table 71); and MPCLK, the MP3 Clock Divider

Figure 12-1 shows the MP3 decoder block diagram.

Figure 12-1. MP3 Decoder Block Diagram

12.1.2

MP3 Data

The MP3 decoder does not start any frame decoding before having a complete frame in its input

buffer(1). In order to manage the load of MP3 data in the frame buffer, a hardware handshake

MPEN

MP3CON.7

MP3

CLOCK

Audio Data

From C51

1K Bytes

MPxREQ

MP3STA1.n

Header Checker

Stereo Processor

Huffman Decoder

IMDCT

Side Information

ERRxxx

MP3STA.5:3

Sub-band

Synthesis

Decoded Data

To Audio Interface

Anti-Aliasing

MPFS1:0

MP3STA.2:1

Dequantizer

MPVER

MP3STA.0

MPBBST

MP3CON.6

MP3VOL

MP3VOR

MP3BAS

MP3MED

MP3TRE

Ancillary Buffer

MP3ANC

Frame Buffer

MP3DAT

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