WM8771 datasheet(18/44 Pages) WOLFSON

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WM8771

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PP Rev 2.0 December 2001

AUDIO INTERFACE FORMATS

Audio data is applied to the internal DAC filters, or output from the ADC filters, via the Digital Audio

Interface. 5 popular interface formats are supported:

•

Left Justified mode

•

Right Justified mode

•

I2S mode

•

DSP Early mode

•

DSP Late mode

All 5 formats send the MSB first and support word lengths of 16, 20, 24 and 32 bits, with the

exception of 32 bit right justified mode, which is not supported.

In left justified, right justified and I2S modes, the digital audio interface receives DAC data on the

DIN1/2/3/4 inputs and outputs ADC data on DOUT. Audio Data for each stereo channel is time

multiplexed with ADCLRC/DACLRC indicating whether the left or right channel is present.

ADCLRC/DACLRC is also used as a timing reference to indicate the beginning or end of the data

words.

In left justified, right justified and I2S modes, the minimum number of BCLKs per DACLRC/ADCLRC

period is 2 times the selected word length. ADCLRC/DACLRC 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

ADCLRC/DACLRC is acceptable provided the above requirements are met.

In DSP early or DSP late mode, all 8 DAC channels are time multiplexed onto DIN1. DACLRC is

used as a frame sync signal to identify the MSB of the first word. The minimum number of BCLKs

per DACLRC period is 8 times the selected word length. Any mark to space ratio is acceptable on

DACLRC provided the rising edge is correctly positioned. The ADC data may also be output in DSP

early or late modes, with ADCLRC used as a frame sync to identify the MSB of the first word. The

minimum number of BCLKs per ADCLRC period is 2 times the selected word length

LEFT JUSTIFIED MODE

In left justified mode, the MSB of DIN1/2/3/4 is sampled by the WM8771 on the first rising edge of

BCLK following a DACLRC transition. The MSB of the ADC data is output on DOUT and changes on

the same falling edge of BCLK as ADCLRC and may be sampled on the rising edge of BCLK.

ADCLRC and DACLRC are high during the left samples and low during the right samples (Figure 11).

LEFT CHANNEL

RIGHT CHANNEL

DACLRC/

ADCLRC

BCLK

DIN1/2/3/4/

DOUT

1/fs

n-2 n-1

LSB

MSB

n-2 n-1

LSB

MSB

Figure 11 Left Justified Mode TIming Diagram

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