AT83SND2CMP3 datasheet(13/97 Pages) ATMEL

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AT83SND2CMP3

7524B–MP3–05/06

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 hard-

ware handshake consisting of data request and data acknowledgment is implemented.

Each time the MP3 decoder needs MP3 data, it sets the MPREQ, MPFREQ and

MPBREQ flags respectively in MP3STA and MP3STA1 registers. MPREQ flag can gen-

erate an interrupt if enabled as explained in Section “Interrupt”. The CPU must then load

data in the buffer by writing it through MP3DAT register thus acknowledging the previ-

ous request. As shown in Figure 10, the MPFREQ flag remains set while data (i.e a

frame) is requested by the decoder. It is cleared when no more data is requested and

set again when new data are requested. MPBREQ flag toggles at every Byte writing.

Note:

1. The first request after enable, consists in 1024 Bytes of data to fill in the input buffer.

Figure 10. Data Timing Diagram

MP3 Clock

The MP3 decoder clock is generated by division of the PLL clock. The division factor is

given by MPCD4:0 bits in MP3CLK register. Figure 11 shows the MP3 decoder clock

generator and its calculation formula. The MP3 decoder clock frequency depends only

on the incoming MP3 frames.

Figure 11. MP3 Clock Generator and Symbol

As soon as the frame header has been decoded and the MPEG version extracted, the

minimum MP3 input frequency must be programmed according to Table 14.

Table 14. MP3 Clock Frequency

MPFREQ Flag

MPBREQ Flag

MPREQ Flag

Cleared when Reading MP3STA

Write to MP3DAT

MPEG Version

Minimum MP3 Clock (MHz)

I21

10.5

MPCD4:0

MP3CLK

MP3 Decoder Clock

MP3clk

PL Lclk

MPC D

----------------------------

MP3

CLOCK

MP3 Clock Symbol

PLL

CLOCK

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