Datasheet

Application for Interfacing With an External Digital Filter
Pin Assignment When Using the External Digital Filter Interface
Audio Format
MSB
16
BCK
DATA, DATAL,DATAR
1/4 f
S
or1/8f
S
WDCK
AudioDataWord=16-Bit
AudioDataWord=32-Bit
AudioDataWord=24-Bit
1 2 3 4 5 6 7 8 9 10 11 12 13 14 151615
LSB
2819 20 21 22 23 24 25 26 273231 3229 30 31
161 2 3 4 5 6 7 8 9 10 11 12 13 14 152423 2017 18 19 2421 22 23
DATA, DATAL,DATAR
DATA, DATAL,DATAR
MSB
LSB
MSB
LSB
1 2 3 4 5
PCM1795
SLES248 MAY 2009 ........................................................................................................................................................................................................
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For some applications, it may be desirable to use an external digital filter to perform the interpolation function, as
it can provide improved stop-band attenuation when compared to the internal digital filter of the PCM1795.
The PCM1795 supports several external digital filters, including:
Texas Instruments DF1704 and DF1706
Pacific Microsonics PMD200 HDCD filter/decoder IC
Programmable digital signal processors (DSPs)
The external digital filter application mode is accessed by programming the following bits in the corresponding
control register:
DFTH = 1 (register 20)
The pins used to provide the serial interface for the external digital filter are illustrated in Figure 55 . The word
clock (WDCK) signal must be operated at 8 times or 4 times the desired sampling frequency, f
S
.
LRCK (pin 4): WDCK as word clock input
BCK (pin 6): Bit clock for audio data
DATA (pin 5): Monaural audio data input when the DFMS bit is not set to '1'
ZEROL (pin 1): DATAL as left channel audio data input when the DFMS bit is set to '1'
ZEROR (pin 2): DATAR as right channel audio data input when the DFMS bit is set to '1'
The PCM1795 in the external digital filter interface mode supports right-justified audio formats including 16-bit,
24-bit, and 32-bit audio data, as shown in Figure 56 . The audio format is selected by the FMT[2:0] bits of control
register 18.
Figure 56. Audio Data Input Format for External Digital Filter (Internal DF Bypass Mode) Application
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