WM8978_06 Wolfson Microelectronics Ltd., WM8978_06 Datasheet - Page 80

• Manufacturer Part Number: WM8978_06
• Description: Stereo Codec With Speaker Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8978
AUDIO SAMPLE RATES
MASTER CLOCK AND PHASE LOCKED LOOP (PLL)
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Table 58 Sample Rate Control
The PLL can be enabled or disabled by the PLLEN register bit.
Note: In order to minimise current consumption, the PLL is disabled when the VMIDSEL[1:0] bits are
set to 00b. VMIDSEL[1:0] must be set to a value other than 00b to enable the PLL.
Table 59 PLLEN Control Bit
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.
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 and/or GPI04) a clock for another part of the system that is
derived from an existing audio master clock.
Figure 43 shows the PLL and internal clocking arrangment on the WM8978.
R7
Additional
Control
R1
Power
management 1
REGISTER
ADDRESS
REGISTER
ADDRESS
3:1
BIT
5
BIT
SR
LABEL
PLLEN
LABEL
000
0
DEFAULT
DEFAULT
PLL enable
0=PLL off
1=PLL on
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
DESCRIPTION
DESCRIPTION
PP Rev 3.0 May 2006
Pre-Production
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