WM8731 Wolfson Microelectronics Ltd., WM8731 Datasheet - Page 38

• Manufacturer Part Number: WM8731
• Description: WM8731 : Low Power Audio Codec With Integrated Headphone Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8731
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.
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.
0001000
Sampling
Control
REGISTER
ADDRESS
0
1
5:2
BIT
USB/
NORMAL
BOSR
SR[3:0]
LABEL
0
0
0000
DEFAULT
Mode Select
1 = USB mode (250/272fs)
0 = Normal mode (256/384fs)
Base Over-Sampling Rate
USB Mode
0 = 250fs
1 = 272fs
ADC and DAC sample rate control;
See USB Mode and Normal Mode
Sample Rate sections for operation
DESCRIPTION
AI Rev 2.3 August 2001
Advanced Information
Normal Mode
0 = 256fs
1 = 384fs
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