Datasheet

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SLES071B − MARCH 2003 − REVISED NOVEMBER 2006
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17
AUDIO DATA INTERFACE
Audio Serial Interface
The audio interface port is a 3-wire serial port. It includes LRCK (pin 1), BCK (pin 2), and DATA (pin 3). BCK is the
serial audio bit clock, and it is used to clock the serial data present on DATA into the serial shift register of the audio
interface. Serial data is clocked into the PCM1791A on the rising edge of BCK. LRCK is the serial audio left/right word
clock.
The PCM1791A requires the synchronization of LRCK and the system clock, but does not need a specific phase
relationship between LRCK and the system clock.
If the relationship between LRCK and system clock changes more than ±6 BCK, internal operation is initialized within
1/f
S
and analog outputs are forced to the bipolar zero level until resynchronization between LRCK and the system
clock is completed.
PCM Audio Data Formats and Timing
The PCM1791A supports industry-standard audio data formats, including standard right-justified, I
2
S, and
left-justified. The data formats are shown in Figure 28. Data formats are selected using the format bits, FMT[2:0],
in control register 18. The default data format is 24-bit I
2
S. All formats require binary 2s complement, MSB-first audio
data. Figure 27 shows a detailed timing diagram for the serial audio interface.
DATA
t
(BCH)
1.4 V
BCK
LRCK
t
(BCL)
t
(LB)
t
(BCY)
t
(DS)
t
(DH)
1.4 V
1.4 V
t
(BL)
PARAMETERS MIN MAX UNITS
t
(BCY)
BCK pulse cycle time 70 ns
t
(BCL)
BCK pulse duration, LOW 30 ns
t
(BCH)
BCK pulse duration, HIGH 30 ns
t
(BL)
BCK rising edge to LRCK edge 10 ns
t
(LB)
LRCK edge to BCK rising edge 10 ns
t
(DS)
DATA setup time 10 ns
t
(DH)
DATA hold time 10 ns
— LRCK clock data 50% ± 2 bit clocks
Figure 27. Timing of Audio Interface