WM8731 datasheet(36/56 Pages) WOLFSON

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WM8731

Advanced Information

WOLFSON MICROELECTRONICS LTD

AI Rev 2.0 February 2001

As a master mode device the WM8731 controls the sequencing of data transfer (ADCDAT,

DACDAT) and output of clocks (BCLK, ADCLRC, DACLRC) over the digital audio interface. It uses

the timing generated from either its on-board crystal or the MCLK input as the reference for the clock

and data transitions. This is illustrated in Figure 29. ADCDAT is always an output from and DACDAT

is always an input to the WM8731 independent of master or slave mode.

BCLK

ADCDAT

ADCLRC

DACDAT

DACLRC

WM8731

CODEC

DSP

ENCODER/

DECODER

Note: ADC and DAC can run at different rates

Figure 29 Master Mode

As a slave device the WM8731 sequences the data transfer (ADCDAT, DACDAT) over the digital

audio interface in response to the external applied clocks (BCLK, ADCLRC, DACLRC). This is

illustrated in Figure 30.

BCLK

ADCDAT

ADCLRC

DACDAT

DACLRC

WM8731

CODEC

DSP

ENCODER/

DECODER

Note: The ADC and DAC can run at different rates

Figure 30 Slave Mode

Note that the WM8731 relies on controlled phase relationships between audio interface BCLK,

DACLRC and the master MCLK or CLKOUT. To avoid any timing hazards, refer to the timing section

for detailed information.

AUDIO DATA SAMPLING RATES

The WM8731 provides for two modes of operation (normal and USB) to generate the required DAC

and ADC sampling rates. Normal and USB modes are programmed under software control according

to the table below.

In Normal mode, the user controls the sample rate by using an appropriate MCLK or crystal

frequency and the sample rate control register setting. The WM8731 can support sample rates from

8ks/s up to 96ks/s.

In USB mode, the user must use a fixed MLCK or crystal frequency of 12MHz to generate sample

rates from 8ks/s to 96ks/s. It is called USB mode since the common USB (Universal Serial Bus)

clock is at 12MHz and the WM8731 can be directly used within such systems. WM8731 can

generate all the normal audio sample rates from this one Master Clock frequency, removing the need

for different master clocks or PLL circuits.

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