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CALCULATION OF ACTUAL SAMPLING FREQUENCY

DIR9001

SLES198 – DECEMBER 2006

The DIR9001 calculates the actual sampling frequency of the biphase input signal and outputs its result through

dedicated pins.

To use this function, a 24.576-MHz clock source must be supplied to the XTI pin. The 24.576-MHz clock is used

as a measurement reference clock to calculate the actual sampling frequency.

If the XTI pin is connected to DGND, calculation of the actual sampling frequency is not performed.

If there is an error in the XTI clock frequency, the calculation result and range are shifted correspondingly.

This output is the result of calculating the sampling frequency, it is not the sampling frequency information of the

channel-status data (bit 24–bit 27).

The sampling frequency information of the channel-status data (bit 24–bit 27) is not output through these pins.

The calculation result is decoded into 2-bit data, which is output on the FSOUT[1:0] pins.

If the PLL is locked but the sampling frequency is out-of-range, or if the PLL is unlocked, FSOUT[1:0] = HL is

output to indicate an abnormality.

When the XTI source clock is not supplied before power on, FSOUT [1:0] always outputs LL.

The calculated value is held until reset.

The relationship between the FSOUT[1:0] outputs and the range of sampling frequencies is shown in Table 11.

Table 11. Calculated Sampling Frequency Output

ACTUAL SAMPLING FREQUENCY

CALCULATED SAMPLING FREQUENCY OUTPUT

RANGE

FSOUT1

FSOUT0

Out of range

Out of range or PLL unlocked

H

L

32 kHz

31.2 kHz–32.8 kHz

H

H

44.1 kHz

43 kHz–45.2 kHz

L

L

48 kHz

46.8 kHz–49.2 kHz

L

H

24

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