WM8955 datasheet(31/43 Pages) WOLFSON

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WM8955L

Product Preview Rev 0.4 May2003

AUDIO SAMPLE RATES

The WM8955L supports a wide range of master clock frequencies on the MCLK pin, and can

generate manycommonlyused audio sample rates directlyfrom the master clock.

There are two clocking modes:

•

‘Normal’ mode supports master clocks of 128fs, 192fs, 256fs, 384fs, and their multiples

•

USB mode supports 12MHz or 24MHz master clocks. This mode is intended for use in

systems with a USB interface, and runs without a PLL.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

USB

Clocking Mode Select

1: USB Mode

0: ‘Normal’ Mode

5:1

SR [4:0]

0000

Sample Rate Control

6MCLK

DIV2

MCLK Divide by2

0: Divide disabled

1: Divide enabled

R8 (08h)

Sample Rates

7CLKOUT

DIV2

MCLK Divide by2

0: Divide disabled

1: Divide enabled

Table 22 Clocking andSample Rate Control

The clocking of the WM8955L is controlled using the MCLKDIV2, USB, and SR control bits. Setting

the MCLKDIV2 bit divides MCLK bytwo internally. The USB bit selects between ‘Normal’ and USB

mode. Each combination of the SR4 to SR0 control bits selects one MCLK division ratio and hence

one sample rate (see next page). The digital filter characteristics are automaticallyadjusted to suit

the MCLK and sample rate selected (see Digital Filter Characteristics).

Since all sample rates are generated bydividing MCLK, their accuracydepends on the accuracyof

MCLK. If MCLK changes, the sample rates change proportionately. Note that some sample rates

(e.g. 44.1kHz in USB mode) are approximated, i.e. theydiffer from their target value bya verysmall

amount. This is not audible, as the maximum deviation is only0.27% (8.0214kHz instead of 8kHz in

USB mode - for comparison, a half-tone step corresponds to a 5.9% change in pitch).

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