WM8987 datasheet(36/59 Pages) WOLFSON

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WM8987L

Production Data

PD Rev 4.0 August 2008

DIGITAL AUDIO INTERFACE

The digital audio interface is used for inputting DAC data into the WM8987L and outputting ADC data

from it. It uses five pins:

•

ADCDAT: ADC data output

•

ADCLRC: ADC data alignment clock

•

DACDAT: DAC data input

•

DACLRC: DAC data alignment clock

•

BCLK: Bit clock, for synchronisation

The clock signals BCLK, ADCLRC and DACLRC can be outputs when the WM8987L operates as a

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

Three different audio data formats are supported:

•

I2S

•

DSP mode

•

Left justified

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 WM8987L can be configured as either a master or slave mode device. As a master device the

WM8987L generates BCLK, ADCLRC and DACLRC and thus controls sequencing of the data

transfer on ADCDAT and DACDAT. In slave mode, the WM8987L responds with data to clocks it

receives over the digital audio interface. The mode can be selected by writing to the MS bit (see

Table 23). Master and slave modes are illustrated below.

Figure 11 Master Mode

Figure 12 Slave Mode

Note: For optimum ADC audio performance in slave mode, the BCLK input signal should be

configured to transition at the same time as the falling edge of MCLK.

The ADCDAT digital data output is buffered inside the CODEC using a digital logic buffering block.

However, the ADCDAT buffering block is not reset by the power-on reset circuit and hence the

ADCDAT pin stage (logic high or logic low) is undefined at power up until data is clocked out from the

ADC. Implementation of either of these workarounds will ensure correct operation:

•

Ensure that any external connection to the ADCDAT pin is made with the understanding

that ADCDAT pin may be driven high or low by the CODEC until ADC data is clocked out.

•

Tri-state the ADCDAT output pin by setting the TRI bit in R24 (Additional Control 2

(as the CODEC has no internal pull-up/down resistors) the input voltage level must be set

on these pins by an external source (either the device connected to the digital audio

interface or pull-up/down resistors) to prevent excess current consumption.

WM8987 Datasheet(PDF) 36 Page - Wolfson Microelectronics plc

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