WM8501

Production Data

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PD, Rev 4.2, July 2009

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 WM8501, MCLK is used to derive clocks for the DAC path. The DAC path

consists of 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 powered down 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:

•

Right Justified mode

•

I

•

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 of 16-bits may be used.

may be used. (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 DSP compatible format is selected. Mode

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

‘Packed’ mode (i.e. only 32 or 48 clocks per LRCLK period) operation is also supported in both

applied (16 BCLKS per LRCLK half period), the device auto-detects this mode and switches to

16-bit data length.

I

multiplexed 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.

length. LRCLK must be high for a minimum of word length BCLKs and low for a minimum of word

length BCLKs. Any mark to space ratio on LRCLK is acceptable provided the above requirements

transition. LRCLK is low during the left samples and high during the right samples.