WM8940CGEFLSLASHV datasheet(51/88 Pages) CIRRUS

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WM8940

Rev 4.4

DIGITAL AUDIO INTERFACES

The audio interface has four pins:

•

ADCDAT: ADC data output

•

DACDAT: DAC data input

•

FRAME: Data alignment clock

•

BCLK: Bit clock, for synchronisation

The clock signals BCLK, and FRAME can be outputs when the WM8940 operates as a master, or

inputs when it is a slave (see Master and Slave Mode Operation, below).

Four different audio data formats are supported:

•

Left justified

•

Right justified

•

I2S

•

DSP mode A / B

All of these modes are MSB first. They are described in Audio Data Formats, below. Refer to the

Electrical Characteristic section for timing information.

MASTER AND SLAVE MODE OPERATION

The WM8940 audio interface may be configured as either master or slave. As a master interface

device the WM8940 generates BCLK and FRAME and thus controls sequencing of the data transfer

on ADCDAT and DACDAT. To set the device to master mode register bit MS should be set high. In

slave mode (MS=0), the WM8940 responds with data to clocks it receives over the digital audio

interfaces.

AUDIO DATA FORMATS

In Left Justified mode, the MSB is available on the first rising edge of BCLK following an FRAME

transition. The other bits up to the LSB are then transmitted in order. Depending on word length,

BCLK frequency and sample rate, there may be unused BCLK cycles before each FRAME transition.

LEFT

PHASE

RIGHT

PHASE

FRAME

BCLK

DACDAT /

ADCDAT

1/fs

n-2 n-1

LSB

MSB

Figure 25 Left Justified Audio Interface (assuming n-bit word length)

In Right Justified mode, the LSB is available on the last rising edge of BCLK before a FRAME

transition. All other bits are transmitted before (MSB first). Depending on word length, BCLK

frequency and sample rate, there may be unused BCLK cycles after each FRAME transition.

WM8940CGEFL/V Datasheet(PDF) 51 Page - Cirrus Logic

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