Datasheet

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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.
When the XTI source clock is stopped, the f
S
calculator holds the last value of the f
S
calculator result.
If XTI source clock is supplied, the f
S
calculator resumes operation.
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
NOMINAL f
S
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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