WM8742GEDSSLASHV datasheet(22/66 Pages) CIRRUS

22 / 66 page

WM8742

Rev 4.4

PCM DIGITAL AUDIO INTERFACE

Audio data is applied to the DAC system via the Digital Audio Interface.

Five popular interface

formats are supported:



Left Justified mode



Right Justified mode



I2S mode



DSP mode A



DSP mode B

All five formats require the MSB to be transmitted first, and support word lengths of 16, 20, 24 and 32

bits, with the exception that 32 bit data is not supported in right justified mode. DIN and LRCLK may

be configured to be sampled on the rising or falling edge of BCLK by adjusting register bits LRP and

BCP.

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

on the DIN input pin. Stereo audio data is time multiplexed on DIN, 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.

The minimum number of BCLK periods per LRCLK period is two times the selected word length.

LRCLK must be high for a period equal to the minimum number of BCLK periods, and low for a

minimum of the same period. Any mark-to-space ratio on LRCLK is acceptable provided the above

requirements are met.

The WM8742 will automatically detect when data with a LRCLK period of exactly 32 BCLKs is

received, and select 16-bit mode.

This overrides any previously programmed word length.

The

operating word length will revert to a programmed value only if a LRCLK period other than 32 BCLKs

is detected.

In DSP mode A or DSP mode B, the data is time multiplexed onto DIN. LRCLK is used as a frame

sync signal to identify the MSB of the first word. The minimum number of BCLKs per LRCLK period is

two times the selected word length. Any mark to space ratio is acceptable on LRCLK provided the

rising edge is correctly positioned.

LEFT JUSTIFIED MODE

In left justified mode, the MSB is sampled on the first rising edge of BCLK following a LRCLK

transition. LRCLK is high during the left data word and low during the right data word.

LEFT CHANNEL

RIGHT CHANNEL

1/fs

n-2 n-1

LSB

MSB

n-2 n-1

LSB

MSB

LRCLK

BCLK

DIN

Figure 14 Left Justified Mode Timing Diagram

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