Datasheet

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XTI Clock Source and Oscillation Amplifier Description
Resonator
XTI
Crystal
OSC
Circuit
24.576MHz
InternalClock
DIR9001
ResonatorConnection
XTO
C
L1
C
L2
R
d
External
Clock
MustBe
Open
XTI
XTO
Crystal
OSC
Circuit
24.576MHz
InternalClock
DIR9001
ExternalClockInputConnection
DIR9001
SLES198 – DECEMBER 2006
This clock, driven by the built-in oscillation amplifier or input into the XTI pin from an external clock, is defined as
the XTI source. A 24.576-MHz fundamental resonator or external 24.576-MHz clock is used as the XTI source.
The DIR9001 requires an XTI source for following purposes:
• The measurement reference clock of actual-sampling-frequency calculator
• The clock source for the XTI source mode (CKSEL = H setting)
(That is, the DIR9001 does not require an XTI source if it is only decoding the biphase input signal.)
The XTI clock source is supplied in one of the following two ways; the details are described in Figure 9 .
• Setting up an oscillation circuit by connecting a resonator with the built-in amplifier
• Applying a clock from an external oscillator circuit or oscillator module
To set up an oscillation circuit by connecting a resonator with the built-in amplifier:
• Connect a 24.576-MHz resonator between the XTI pin and XTO pin.
• The resonator should be a fundamental-mode type.
• A crystal resonator or ceramic resonator can be used.
• The load capacitor C
L1
, C
L2
, and the current-limiting resistor R
d
depend on the characteristics of the
resonator.
• No external feedback resistor between the XTI pin and XTO pin is required, as an appropriate resistor is
incorporated in the device.
• No load other than the resonator is allowed on the XTO pin.
To connect an external oscillator circuit or oscillator module:
• Provide a 24.576-MHz clock on the XTI pin
• Note that the XTI pin is not 5-V tolerant; it is simple CMOS input.
• The XTO pin must be open.
Figure 9. XTI and XTO Connection Diagram
Description of oscillation amplifier operation:
• The built-in oscillation amplifier is always working.
• If the XTI source clock is not used, then the XTI pin must be connected to DGND.
• For reducing power dissipation, it is recommended to not use the XTI source clock.
In XTI mode (CKSEL = H), output clocks (SCKO, BCKO, LRCKO) are generated from XTI source clock.
The relation between output clock frequency (SCKO, BCKO, LRCKO) and the XSCK pin setting in XTI source
mode is shown in Table 6 .
Table 6. SCKO, BCKO, LRCKO Output Frequency at XTI Mode
XTI FREQUENCY OUTPUT CLOCK FREQUENCY IN XTI SOURCE MODE (CKSEL = H)
SCKO BCKO LRCKO
24.576 MHz 24.576 MHz 6.144 MHz 96 kHz
16
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