AT83SND2CMP3B datasheet(66/241 Pages) ATMEL

66 / 241 page

4341F–MP3–03/06

AT8xC51SND2C/MP3B

13.3.3

CRC Error

When the CRC of a frame does not match the one calculated, the flag ERRCRC in MP3STA is

set. In this case, depending on the CRCEN bit in MP3CON, the frame is played or rejected. In

both cases, noise may appear at audio output.

13.4

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 13-4. MPVER bit

gives the MPEG version (2 or 1).

Table 13-4.

MP3 Frame Frequency Sampling

13.5

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 13-4, 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 13-4. Ancillary Data Block Diagram

13.6

Interrupt

13.6.1

Description

As shown in Figure 13-5, 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.

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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