WM8955BLGECOSLASHRV datasheet(31/44 Pages) WOLFSON

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Production Data

WM8955BL

PD Rev 4.1 February 2007

AUDIO SAMPLE RATES

The WM8955BL supports a wide range of master clock frequencies and can generate many

commonly used audio sample rates directly from 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 can run without a PLL.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

USB

Clocking Mode Select

1: USB Mode

0: ‘Normal’ Mode

5:1

SR [4:0]

00000

Sample Rate Control

MCLK DIV2

MCLK Divide by 2

0: Divide disabled

1: Divide enabled

R8 (08h)

Sample Rates

BCLKDIV2

Divide BITCLK output by 2

(use only in USB master mode, i.e.

when USB=1, MS=1)

1 = BCLK is divided by 2 (Note 1)

0 = BCLK is not divided

Table 22 Clocking and Sample Rate Control

Note:

With BCLKDIV2=1, the LRCLK output produces a non-50:50 duty cycle if BCLK/LRCLK is not an

even integer.

The clocking of the WM8955BL is controlled using the MCLKDIV2, USB, and SR control bits. Setting

the MCLKDIV2 bit divides MCLK by two 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 Table 23). The digital filter characteristics are automatically adjusted to suit the

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

Since all sample rates are generated by dividing MCLK, their accuracy depends on the accuracy of

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. they differ from their target value by a very small

amount. This is not audible, as the maximum deviation is only 0.27% (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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