PCM1795DB datasheet(42/58 Pages) TI

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FUNCTIONS AVAILABLE IN THE EXTERNAL DIGITAL FILTER MODE

FMT[2:0]: Audio Data Format Selection

OS[1:0]:

ΔΣ Modulator Oversampling Rate Selection

PCM1795

SLES248 – MAY 2009 ........................................................................................................................................................................................................ www.ti.com

The external digital filter mode is selected by setting DSD = 0 (register 20, B5) and DFTH = 1 (register 20, B4).

The external digital filter mode allows access to the majority of the PCM1795 mode control functions.

Table 12 shows the register mapping available when the external digital filter mode is selected, along with

descriptions of functions that are modified when using this mode selection.

Table 12. External Digital Filter Register Map

B15

B14

B13

B12

B11

B10

R/W

X(1)

R/W

FMT2

FMT1

FMT0

R/W

REV

OPE

DFMS

INZD

R/W

SRST

MONO

CHSL

OS1

OS0

R/W

PCMZ

ZFGR

ZFGL

(1)

Function is disabled. No operation even if data bit is set.

Default value: 000

FMT[2:0]

Audio Data Format Selection

000

16-bit right-justified format

001

32-bit right-justified format

010

24-bit right-justified format (default)

Other

N/A

Default value: 00

OS[1:0]

Operation Speed Selection

8 times WDCK (default)

4 times WDCK

16 times WDCK

Reserved

The effective oversampling rate is determined by the oversampling performed by both the external digital filter

and the

ΔΣ modulator. For example, if the external digital filter is 8× oversampling, and OS[1:0] = 00 is selected,

then the

ΔΣ modulator oversamples by 8×, resulting in an effective oversampling rate of 64×. The 16× WDCK

oversampling rate is not available above a 100-kHz sampling rate. If the oversampling rate selected is 16×

WDCK, the system clock frequency must be over 256 fS.

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