WM8521

Production Data

w

PD Rev 4.1 August 2006

10

CLOCKING SCHEMES

In a typical digital audio system there is only one central clock source producing a reference clock to

which all audio data processing is synchronised. This clock is often referred to as the audio system’s

Master Clock. The external master clock can be applied directly through the MCLK input pin with no

configuration necessary for sample rate selection.

Note that on the WM8521, MCLK is used to derive clocks for the DAC path. The DAC path is

affected by DAC sampling clock, DAC digital filter clock and DAC digital audio interface timing. In a

system where there are a number of possible sources for the reference clock it is recommended that

the clock source with the lowest jitter be used to optimise the performance of the DAC.

The device can be reset by stopping MCLK. In this state the power consumption is substantially

reduced.

DIGITAL AUDIO INTERFACE

Audio data is applied to the internal DAC filters via the Digital Audio Interface.

Three interface

formats are supported:

• I

• Right Justified mode

• DSP mode

All formats send the MSB first. The data format is selected with the FORMAT pin. When FORMAT is

LOW, right justified data format is selected and word lengths up to 16-bits may be used. If a word

length shorter than 16-bits is used, the unused bits should be padded with zeroes.

When the

FORMAT pin is HIGH, I

Unless in 16-bit ‘packed’ mode, if a word length shorter than 24-bits is used, the unused bits should

be padded with zeros. If LRCLK is 4 BCLKs or less duration, the 16bit DSP compatible format is

selected. Mode A and B clock formats are supported, selected by the state of the FORMAT pin.

I

The WM8521 supports word lengths of 16-32 bits in I

In I

with LRCLK indicating whether the left or right channel is present. LRCLK is also used as a timing

reference to indicate the beginning or end of the data words.

25-32 bits: LRCLK must be high for a minimum of data wordlength BCLKs and low for a minimum of

data wordlength BCLKs. The LSBs will be truncated and the most significant 24 bits will be used by

the internal processing.

24 bits: LRCLK must be high for a minimum of 24 BCLKs and low for a minimum of 24 BCLKs.

17-23 bits: Data must be zero padded to 24 bits and LRCLK must be high for a minimum of 24

BCLKs and low for a minimum of 24 BCLKs.

Up to 16 bits: EITHER data must be zero padded to 24 bits and LRCLK must be high for minimum

24 BCLKs and low for 24 BCLKs,

OR data must be zero padded to 16 bits and LRCLK must be high for exactly 16 BCLKs and low for

exactly 16 BCLKs. The device auto-detects this ’16-bit packed’ mode and switches to 16-bit data

length.

Any mark to space ratio on LRCLK is acceptable provided the above requirements are met.