WM8351 datasheet(49/330 Pages) WOLFSON

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Production Data

WM8351

PD, April 2012, Rev 4.5

12.3.1

SYSCLK CONTROL

The MCLK_SEL bit is used to select the source for SYSCLK. The source may be either directly from

the MCLK input or may be from the output of the FLL. If required, the selected source may be divided

by two, as determined by MCLK_DIV, as described in Table 8. For further details of the FLL, see

Section 12.4.

When the internal clock source is switched from one value to another using MCLK_SEL, the change

of source will only occur following a falling edge of the source signal that was originally selected. In

the case where the clock source is switched from FLL to MCLK, a suitable falling edge can be

ensured by disabling the FLL after selection of MCLK as the source.

The recommended sequence of actions to switch from FLL to MCLK source is as follows:



Select MCLK as source (MCLK_SEL = 0)



Disable FLL (FLL_ENA = 0)



Disable FLL oscillator (FLL_OSC_ENA = 0)

Note that, as an alternative to the above sequence, a software reset may be used to re-select MCLK

as the default SYSCLK source.

The recommended sequence of actions to switch from MCLK to FLL source is as follows:



Enable FLL oscillator (FLL_OSC_ENA = 1)



Enable FLL (FLL_ENA = 1)



Select FLL as source (MCLK_SEL = 1)

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R40 (28h)

Clock Control

MCLK_SEL

Selects source for SYSCLK to CODEC

0 = MCLK pin

1 = FLL

MCLK_DIV

Selects MCLK division in slave (MCLK

input) mode:

0 = divide MCLK by 1

1 = divide MCLK by 2

Table 8 SYSCLK Control

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