WM8987LGECOSLASHV datasheet(40/58 Pages) WOLFSON

40 / 58 page

WM8987L

Pre-Production

PP Rev 3.0 January 2007

CLOCK OUTPUT

By default, the ADCLRC pin is the ADC word clock input/output. Under the control of ADCLRM[1:0],

10 or 11 then ADCLRC pin is always an output even in slave mode or when TRI = ‘1’, (see Table 36).

The ADC then uses the DACLRC pin as its LRCLK in both master and slave modes.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R27(1Bh)

Additional

Control (3)

[8:7] ADCLRM

[1:0]

Configures ADCLRC pin

00 = ADCLRC is ADC word clock input (slave

mode) or ADCLRC output (master mode)

01 = ADCLRC pin is MCLK output

10 = ADCLRC pin is MCLK / 5.5 output

11 = ADCLRC pin is MCLK / 6 output

Table 36 ADCLRC Clock Output

CLOCKING AND SAMPLE RATES

The WM8987L supports a wide range of master clock frequencies on the MCLK pin, and can

generate many commonly used audio sample rates directly from the master clock. The ADC and

DAC do not need to run at the same sample rate; several different combinations are possible.

There are two clocking modes:

•

‘Normal’ mode supports master clocks of 128fs, 192fs, 256fs, 384fs, and their multiples

(Note: fs refers to the ADC or DAC sample rate, whichever is faster)

•

USB mode supports 12MHz or 24MHz master clocks. This mode is intended for use in

systems with a USB interface, and eliminates the need for an external PLL to generate

another clock frequency for the audio codec.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

CLKDIV2

Master Clock Divide by 2

1 = MCLK is divided by 2

0 = MCLK is not divided

5:1

SR [4:0]

00000

Sample Rate Control

R8 (08h)

Clocking and

Sample Rate

Control

USB

Clocking Mode Select

1 = USB Mode

0 = ‘Normal’ Mode

Table 37 Clocking and Sample Rate Control

The clocking of the WM8987L is controlled using the CLKDIV2, USB, and SR control bits. Setting the

CLKDIV2 bit divides MCLK by two internally. The USB bit selects between ‘Normal’ and USB mode.

Each value of SR[4:0] selects one combination of MCLK division ratios and hence one combination

of sample rates (see next page). Since all sample rates are generated by dividing MCLK, their

accuracy depends on the accuracy of MCLK. If MCLK changes, the sample rates change

proportionately.

Note that some sample rates (e.g. 44.1kHz in USB mode) are approximated, i.e. they differ from their

target value by a very small amount. This is not audible, as the maximum deviation is only 0.27%

(8.0214kHz instead of 8kHz in USB mode). By comparison, a half-tone step corresponds to a 5.9%

change in pitch.

The SR[4:0] bits must be set to configure the appropriate ADC and DAC sample rates in both master

and slave mode.

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