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CLOCK DESCRIPTION

System Clock Source

DIR9001

SLES198 – DECEMBER 2006

DIR9001 has the following two clock sources for the system clock.

• PLL source (128 f

• XTI source (One 24.576-MHz resonator or external clock source is required.)

Two clock sources are used for the following purpose.

• PLL source: Recovered system clock from the biphase input signal

• XTI source: Clock source for peripheral devices (for example, A/D converter, microcontroller, etc.)

Measurement reference clock for the internal actual-sampling-frequency calculator

Description of PLL clock source

• The PLL clock source is the output clock of built-in PLL (including VCO).

• The PLL clock source frequency is selectable from 128 f

• When the PLL is in the locked condition, the PLL clock source is the clock recovered from the biphase input

signal.

• When PLL is in the unlocked condition, the PLL clock source is the built-in free-running clock of the VCO.

• The frequency of the PLL clock source in the unlocked condition is not constant.

(The VCO free-running frequency is dependent on supply voltage, temperature, and variations in the die’s

wafer.)

Description of XTI clock source

• The XTI clock source is not used to recover the clock and decode data from the biphase input signal.

• Therefore, if the DIR9001 is used only for recovering the clock and decoding data from the biphase input

signal, an XTI clock source is not required. In this case, the XTI pin must be connected to the DGND pin.

(The DIR9001 does not have a selection pin for using an XTI clock source or not using one.)

The selection method of clock source

• The output clock is selected from two clock sources by the level of the CKSEL pin.

• The selection of the system clock source depends only on the input level of CKSEL pin.

• CKSEL = L setting is required for recovering the clock and decoding data from biphase input.

• CKSEL = H setting is required for XTI clock source output.

• The continuity of clock during the clock source transition between the XTI source and the PLL source is not

assured.

Method of automatic clock source selection (CLOCK SOURCE MODE: AUTO)

• This method enables selection of the clock source automatically, using the DIR9001 ERROR status. The PLL

source clock is output when ERROR = L; the XTI source is output when ERROR = H.

• To enable automatic clock source selection, the CKSEL pin must be connected to the ERROR pin.

• If XTI clock source is needed during the ERROR period, this method is recommended.

• Because the clock source during ERROR status is XTI, if an XTI clock source is not provided to the XTI pin,

then SCKO, BCKO, and LRCKO are not output during the ERROR period.

The relationship between the clock/data source and the combination of CKSEL pin and PLL status inputs is

shown in Table 2.

The clock tree system is shown in Figure 7.

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