WM8721

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WOLFSON MICROELECTRONICS LTD

PP Rev 1.3 November 2000

21

REGISTER

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

0

USB/

NORMAL

0

Mode Select

1 = USB mode (250/272fs)

0 = Normal mode (256/384fs)

1

BOSR

0

Base Over-Sampling Rate

USB Mode

0 = 250fs

1 = 272fs

Normal Mode

0 = 256fs

1 = 384fs

0001000

Sampling

Control

5:2

SR[3:0]

000

DAC sample rate control;

See USB Mode and Normal Mode

Sample Rate sections for operation

Table 9 Sample Rate Control

NORMAL MODE SAMPLE RATES

In normal mode MCLK is set up according to the desired sample rates of the DAC. For DAC

sampling rates of 8, 32, 48 or 96KHz, MCLK frequencies of either 12.288MHz (256Fs) or 18.432MHz

(384Fs) can be used. DAC sampling rates of 8, 44.1 or 88.2KHz from MCLK frequencies of either

11.2896MHz (250Fs) or 16.9344MHz (384Fs) can be used.

The table below should be used to set up the device to work with the various sample rate

combinations. Refer to Digital Filter Characteristics section for an explanation of the different filter

types.

SAMPLING

RATE

DAC

MCLK

FREQUENCY

SAMPLE

RATE

REGISTER SETTINGS

DIGITAL

FILTER

TYPE

KHz

MHz

BOSR

SR3

SR2

SR1

SR0

12.288

0

0

0

0

0

48

18.432

1

0

0

0

0

1

12.288

0

0

0

0

1

8

18.432

1

0

0

0

1

1

12.288

0

0

1

1

0

32

18.432

1

0

1

1

0

1

12.288

0

0

1

1

1

96

18.432

1

0

1

1

1

2

11.2896

0

1

0

0

0

44.1

16.9344

1

1

0

0

0

1

11.2896

0

1

0

0

1

8

(Note 1)

16.9344

1

1

0

0

1

1

11.2896

0

1

1

1

1

88.2

16.9344

1

1

1

1

1

2

Table 10 Normal Mode Sample Rate Look-up Table

Notes:

1.

8k not exact, actual = 8.018kHz

2.

All other combinations of BOSR and SR[3:0] that are not in the truth table are invalid

The BOSR bit represents the base over-sampling rate. This is the rate that the WM8721 digital signal

processing is carried out at. In Normal mode, with BOSR = 0, the base over-sampling rate is at

256Fs, with BOSR = 1, the base over-sampling rate is at 384Fs. This can be used to determine the

actual audio data rate required by the DAC.