WM8956 datasheet(48/80 Pages) WOLFSON

48 / 80 page

WM8956

Preliminary Technical Data

PTD, July 2007, Rev 2.1

MASTER MODE DACLRC ENABLE

In master mode, by default DACLRC and BCLK are disabled when the DACs are both disabled.

Figure 31 Master Mode Clock Output Control

COMPANDING

The WM8956 supports A-law and

µ-law companding. Companding can be enabled on the DAC

audio interface by writing the appropriate value to the DACCOMP register bit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

4:3

DACCOMP

DAC companding

00 = off

01 = reserved

10 = µ-law

11 = A-law

R9 (09h)

Audio

Interface (2)

WL8

0 = off

1 = device operates in 8-bit mode.

Table 29 Companding Control

Companding involves using a piecewise linear approximation of the following equations (as set out

by ITU-T G.711 standard) for data compression:

µ-law (where µ=255 for the U.S. and Japan):

F(x) = ln( 1 +

µ|x|) / ln( 1 + µ)

-1 ≤ x ≤ 1

A-law (where A=87.6 for Europe):

F(x) = A|x| / ( 1 + lnA)

} for x ≤ 1/A

F(x) = ( 1 + lnA|x|) / (1 + lnA)

} for 1/A ≤ x ≤ 1

The companded data is also inverted as recommended by the G.711 standard (all 8 bits are inverted

for

µ-law, all even data bits are inverted for A-law). The data will be transmitted as the first 8 MSB’s

of data.

Companding converts 13 bits (

µ-law) or 12 bits (A-law) to 8 bits using non-linear quantization. The

input data range is separated into 8 levels, allowing low amplitude signals better precision than that

of high amplitude signals. This is to exploit the operation of the human auditory system, where louder

sounds do not require as much resolution as quieter sounds.

The companded signal is an 8-bit

word containing sign (1-bit), exponent (3-bits) and mantissa (4-bits).

Setting the WL8 register bit allows the device to operate with 8-bit data. In this mode it is possible to

use 8 BCLK cycles per LRC frame. When using DSP mode B, this allows 8-bit data words to be

output consecutively every 8 BCLK cycles and can be used with 8-bit data words using the A-law

and u-law companding functions.

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