WM8728

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WOLFSON MICROELECTRONICS LTD

PP Rev 1.2 April 2001

12

DIGITAL AUDIO INTERFACE

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

interface formats are supported:

•

Left Justified mode

•

Right Justified mode

•

I

•

DSP Early mode

•

DSP Late mode

All five formats send the MSB 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 LRCIN maybe

configured to be sampled on the rising or falling edge of BCKIN.

In left justified, right justified and I

input. Audio Data is time multiplexed with LRCIN indicating whether the left or right channel is

present. LRCIN is also used as a timing reference to indicate the beginning or end of the data

words. The minimum number of BCKINs per LRCIN period is 2 times the selected word length.

LRCIN must be high for a minimum of word length BCKINs and low for a minimum of word length

BCKINs. Any mark to space ratio on LRCIN is acceptable provided the above requirements are

met

The WM8728 will automatically detect when data with a LRCIN period of exactly 32 BCKINs is

sent, and select 16-bit mode - overriding any previously programmed word length. Word length

will revert to a programmed value only if a LRCIN period other than 32 BCKINs is detected.

In DSP early or DSP late mode, the data is time multiplexed onto DIN. LRCIN is used as a frame

sync signal to identify the MSB of the first word. The minimum number of BCKINs per LRCIN

period is 2 times the selected word length. Any mark to space ratio is acceptable on LRCIN

provided the rising edge is correctly positioned. (See Figure 10 and Figure 11)

LEFT JUSTIFIED MODE

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

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

LEFT CHANNEL

RIGHT CHANNEL

LRCIN

BCKIN

DIN

1/fs

n

3

2

1

n-2 n-1

LSB

MSB

n

3

2

1

n-2 n-1

LSB

MSB

Figure 7 Left Justified Mode Timing Diagram