WM8978 datasheet(59/78 Pages) WOLFSON

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WM8978

PP Rev 1.7 January 2005

AUDIO SAMPLE RATES

The WM8978 sample rates for the ADCs and the DACs are set using the SR register bits. The

cutoffs for the digital filters and the ALC attack/decay times stated are determined using these

values and assume a 256fs master clock rate.

If a sample rate that is not explicitly supported by the SR register settings is required then the

closest SR value to that sample rate should be chosen, the filter characteristics and the ALC attack,

decay and hold times will scale appropriately.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Additional

Control

3:1

000

Approximate sample rate (configures the

coefficients for the internal digital filters):

000=48kHz

001=32kHz

010=24kHz

011=16kHz

100=12kHz

101=8kHz

110-111=reserved

Table 48 Sample Rate Control

MASTER CLOCK AND PHASE LOCKED LOOP (PLL)

The WM8978 has an on-chip phase-locked loop (PLL) circuit that can be used to:

Generate master clocks for the WM8978 audio functions from another external clock, e.g. in

telecoms applications.

Generate and output (on pin CSB/GPIO1) a clock for another part of the system that is derived from

an existing audio master clock.

Figure 30 shows the PLL and internal clocking arrangment on the WM8978.

The PLL can be enabled or disabled by the PLLEN register bit.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

Power

management 1

PLLEN

PLL enable

0=PLL off

1=PLL on

Table 49 PLLEN Control Bit

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