AT83SND1CXXX-ROTIL datasheet(66/212 Pages) ATMEL

66 / 212 page

4109J–8051–10/06

AT8xC51SND1C

12.4

Frame Information

The MP3 frame header contains information on the audio data contained in the frame. These

informations is made available in the MP3STA register for you information. MPVER and

MPFS1:0 bits allow decoding of the sampling frequency according to Table 61. MPVER bit gives

the MPEG version (2 or 1).

Table 61. MP3 Frame Frequency Sampling

12.5

Ancillary Data

MP3 frames also contain data bits called ancillary data. These data are made available in the

MP3ANC register for each frame. As shown in Figure 12-4, the ancillary data are available by

Bytes when MPANC flag in MP3STA register is set. MPANC flag is set when the ancillary buffer

is not empty (at least one ancillary data is available) and is cleared only when there is no more

ancillary data in the buffer. This flag can generate an interrupt as explained in Section "Inter-

rupt", page 66. When set, software must read all Bytes to empty the ancillary buffer.

Figure 12-4. Ancillary Data Block Diagram

12.6

Interrupt

12.6.1

Description

As shown in Figure 12-5, the MP3 decoder implements five interrupt sources reported in ERR-

CRC, ERRSYN, ERRLAY, MPREQ, and MPANC flags in MP3STA register.

All these sources are maskable separately using MSKCRC, MSKSYN, MSKLAY, MSKREQ, and

MSKANC mask bits respectively in MP3CON register.

The MP3 interrupt is enabled by setting EMP3 bit in IEN0 register. This assumes interrupts are

globally enabled by setting EA bit in IEN0 register.

All interrupt flags but MPREQ and MPANC are cleared when reading MP3STA register. The

MPREQ flag is cleared by hardware when no more data is requested (see Figure 12-2) and

MPANC flag is cleared by hardware when the ancillary buffer becomes empty.

MPVER

MPFS1

MPFS0

Fs (kHz)

22.05 (MPEG II)

24 (MPEG II)

16 (MPEG II)

Reserved

44.1 (MPEG I)

48 (MPEG I)

32 (MPEG I)

Reserved

Ancillary

Data To C51

MP3ANC

MPANC

MP3STA.7

7-Byte

Ancillary Buffer

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