MAS3529F datasheet(44/92 Pages) MICRONAS

44 / 92 page

MAS 35x9F

DATA SHEET

June 30, 2004; 6251-505-1DS

Micronas

3.3.7. DSP Volume Control

The digital baseband volume matrix is used for control-

ling the digital gain as shown in Fig. 3–3. This volume

control is effective on both, the digital audio output and

the data stream to the D/A converters. The values are

in 20-bit 2’s complement notation.

Table 3–14 shows the proposed settings for the 4 vol-

ume matrix coefficients for stereo, left and right mono.

The gain factors are given in fixed point notation

(

−1.0×219 = 80000

hex).

If channels are mixed, care must be taken to prevent

clipping at high amplitudes. Therefore, the sum of the

absolute values of coefficients for one output channel

must be less than 1.0.

For normal operating conditions it is recommended to

use the main volume control of the audio codec

instead (register 00 10hex of the audio codec).

Fig. 3–3: Digital volume matrix

3.3.8. Explanation of the G.729A Data Format

The codec is working on a page basis where the

encoding and decoding is performed in blocks of 50

G.729 frames, whereas each frame consists of

10 bytes in byte-swapped order (see Fig. 3–4). There-

fore most changes to the UserControl register become

effective when processing of the current page is fin-

ished. The pages are optionally preceeded by 10 byte

header frames (see Table 3–15).

Switching directly from encoding to decoding mode (or

vice versa) is not allowed. Instead, the controller has to

send a stop request to the MAS 35x9F (writing 0hex to

UserControl) and must keep on sending data in decod-

ing mode or receive data in encoding mode until the

current page of 50 frames is finished. After this run-out

time, the encoding or decoding can be started again.

Fig. 3–4: Schematic timing of the data transmission with preceeding header

−1

left audio

right audio

Table 3–14: Settings for the digital volume matrix

Memory

D0:354

D0:355

D0:356

D0:357

Name

Stereo

(default)

−1.0

Mono left

−1.0

Mono right

−1.0

Table 3–15: Content of page header

Byte

34567

8910

Value

(hex)

...

page

header

frame

page

header

frame

100

page

header

frame

101

frame

102

10 ms 10 ms

byte

64 6D 72 31 64 61 74 61 F4 01

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