WM8978 datasheet(52/78 Pages) WOLFSON

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WM8978

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PP Rev 1.7 January 2005

DIGITAL AUDIO INTERFACES

The audio interface has four pins:

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ADCDAT: ADC data output

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DACDAT: DAC data input

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LRC: Data Left/Right alignment clock

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BCLK: Bit clock, for synchronisation

The clock signals BCLK, and LRC can be outputs when the WM8978 operates as a master, or inputs

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

Five different audio data formats are supported:

•

Left justified

•

Right justified

•

DSP mode A

•

DSP mode 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 WM8978 audio interface may be configured as either master or slave. As a master interface

device the WM8978 generates BCLK and LRC 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 WM8978 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 LRC

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 LRC transition.

Figure 23 Left Justified Audio Interface (assuming n-bit word length)

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