MAS3549F datasheet(17/92 Pages) MICRONAS

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DATA SHEET

MAS 35x9F

Micronas

June 30, 2004; 6251-505-1DS

2.10.MP3 Block Input Mode

A new so-called

MP3 block input mode is now avail-

able which improves the input timing behavior of the

MAS 35x9F MPEG 1/2/2.5 Layer 3 decoder. The fol-

lowing sections provide a detailed description of this

new mode.

2.10.1.Functional Description of the MP3 Block

Input Mode

In MP3 block input, the MAS 35x9F generates a

demand for new input data each time one of its two

input buffers becomes available. The controller then

has to send one block of input data via the serial inter-

face SDIB. The block size is 2048 byte. The demand is

signalized via a pulse on the EOD pin.

Fig. 2–13 shows that the number of interrupts per sec-

ond does not depend on the data rate at the serial

interface. The maximum input data bit clock rate sup-

ported by the MAS 35x9F for all MPEG audio sampling

rates is 1.4 MHz.

Table 2–3 shows the average number of interrupts per

second for several typical MP3 bit rates.

The time period between two interrupts may vary

slightly even for fixed bit rate input streams due to the

MP3 specific bit reservoir.

Fig. 2–13: Data Block Timing Diagram

Table 2–3: MP3 bit rate vs. number of interrupts

Bit Rate

[kbit/s]

Number of Interrupts

[1/s]

320

256

224

192

160

128

112

Interrupt

Data blocks in a) and b) contain the same number of bytes.

Data block a) is sent with a lower data rate than data block b).

SIC

Interrupt

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