Datasheet

AUDIO DATA INTERFACE
Audio Serial Interface
PCM Audio Data Formats and Timing
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)
PCM1795
www.ti.com ........................................................................................................................................................................................................ SLES248 – MAY 2009
The audio interface port is a three-wire serial port. It includes LRCK (pin 4), BCK (pin 6), and DATA (pin 5). 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 are clocked into the PCM1795 on the rising edge of BCK. LRCK is the serial
audio left/right word clock.
The PCM1795 requires the synchronization of LRCK and the system clock, but does not need a specific phase
relation between LRCK and the system clock.
If the relationship between LRCK and the 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.
The PCM1795 supports industry-standard audio data formats, including standard right-justified, I
2
S, and
left-justified. The data formats are illustrated in Figure 38 to Figure 40 . Data formats are selected using the
format bits, FMT[2:0], in control register 18. The default data format is 32-bit I
2
S. All formats require binary twos
complement, MSB-first audio data. Figure 37 and Table 5 show a detailed timing diagram for the serial audio
interface.
Figure 37. Audio Interface Timing
Table 5. Timing Characteristics for Figure 37
PARAMETER MIN MAX UNIT
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
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Product Folder Link(s): PCM1795