WM8731 datasheet(37/56 Pages) WOLFSON

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WM8731

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 February 2001

Uniquely, the WM8731 offers the user the ability to sample the ADC and DAC at different rates under

software control in both Normal and USB modes. The reduces the burden on any controlling DSP.

However, the signal processing in the ADC and DAC over-sampling filters is tightly coupled together

in order to minimise power consumption. To this end, only the combinations of sample rates listed in

the following sections are supported. Note that these rates supported are anticipated to be the likely

combinations used in typical audio systems.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

USB/

NORMAL

Mode Select

1 = USB mode (250/272fs)

0 = Normal mode (256/384fs)

BOSR

Base Over-Sampling Rate

USB Mode

0 = 250fs

1 = 272fs

Normal Mode

0 = 256fs

1 = 384fs

0001000

Sampling

Control

5:2

SR[3:0]

0000

ADC and DAC sample rate control;

See USB Mode and Normal Mode

Sample Rate sections for operation

Table 16 Sample Rate Control

NORMAL MODE SAMPLE RATES

In normal mode MCLK/crystal oscillator is set up according to the desired sample rates of the ADC

and DAC. For ADC or DAC sampling rates of 8, 32, 48 or 96kHz, MCLK frequencies of either

12.288MHz (256fs) or 18.432MHz (384fs) can be used. For ADC or DAC sampling rates of 8, 44.1 or

88.2kHz from MCLK frequencies of either 11.2896MHz (256fs) or 16.9344MHz (384fs) can be used.

The table below should be used to set up the device to work with the various sample rate

combinations. For example if the user wishes to use the WM8731 in normal mode with the ADC and

DAC sample rates at 48kHz and 48kHz respectively then the device should be programmed with

BOSR = 0, SR3 = 0, SR2 = 0, SR1 = 0 and SR0 = 0 with a 12.288MHz MCLK or with BOSR = 1,

SR3 = 0, SR2 = 0, SR1 = 0 and SR0 = 0 with a 18.432MHz MCLK. The ADC and DAC will then

operate with a Digital Filter of type 1, refer to Digital Filter Characteristics section for an explanation

of the different filter types.

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