PCM9211
SBAS495 –JUNE 2010
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DIR: Auto Source Selector for Main Output and AUX Output
The AUTO source selector is an automatic system that selects the DIR or ADC output based on specific DIR
conditions set by Register 26h. The AUTO source selector is integrated in both the Main Port and the AUX
output separately.
The typical behavior for the AUTO source selector is shown in Figure 30. This example is the default register
setting for Register 26h. In this case, only Register 26h/AUNLOCK is selected.
Non-Biphase
Biphase
Non-Biphase
RXINx
Built-in PLL
Status
Unlock
Lock
Unlock
XTI Status
Normal Operation
CLKST
tCLKST1
tCLKST2
ERROR
tXTIWT
SCKO, BCK,
LRCK
XTI (ADC) Source
DIR Source
XTI (ADC) Source
MUTE
DOUT
ADC Source
MUTE
DIR Source
ADC Source
Figure 30. Typical Behavior for AUTO Source Selector
When the DIR is unlocked, the ADC output is automatically routed to the Main Output Port.
Polarity of the CLKST signal is configured by Register 22h/CLKSTP. The default is active low, which means that
clock source either changes from DIR to ADC, or from ADC to DIR.
If the DIR is locked, then the DIR output is routed to the Main Output Port automatically after tCLKST1. During that
period, the output port is muted. tCLKST1 can be configured using Register 23h/ERRWT[1:0]. tCLKST2 is 50 ms,
providing that an XTI clock of 24.576 MHz is applied.
If the DIR loses its lock a subsequent time, the ADC output is routed to the Main Output Port automatically after
tXTIWT. Once again, the output port is muted during this time. tXTIWT can be configured using Register
23h/XTIWT[1:0].
The auto source selector can be triggered by the following changes in the DIR (Register 26h is used to select
which variable to use as the trigger):
•
•
•
•
•
DIR error (discussed earlier in DIR: Errors and Interrupts; configured by Register 25h)
Out-of-range sampling frequency
Non-PCM data
When the Validity flag in the S/PDIF stream is '1'
When the PLL is unlocked (default)
38
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