Datasheet
ADN2814 Data Sheet
Rev. C | Page 20 of 28
For example, if the reference clock frequency is 32 MHz,
SEL_RATE = 1, since the CTRLA[7:6] setting is [01], because
the reference frequency falls into the 20 MHz to 40 MHz range.
Assume for this example that the input data rate is 622.08 Mb/s
(OC12). After following Step 1 through Step 4, the value that is
read back on FREQ[22:0] = 0x9B851, which is equal to 637 ×
10
3
. Plugging this value into the equation yields
to configure the ADN2814 to use the correct reference
frequency range by setting two bits of the CTRLA register,
CTRLA[7:6]. Using the reference clock to determine the
frequency of the incoming data does not affect the manner in
which the part locks onto data. In this mode, the reference clock
is used only to determine the frequency of the data. For this
reason, the user does not need to know the data rate to use the
reference clock in this manner.
637e3 × 32e6/2
(14 + 1)
= 622.08 Mb/s
Prior to reading back the data rate using the reference clock, the
CTRLA[7:6] bits must be set to the appropriate frequency range
with respect to the reference clock being used. A fine data rate
readback is then executed as follows:
If subsequent frequency measurements are required, CTRLA[1]
should remain set to 1. It does not need to be reset. The
measurement process is reset by writing a 1 followed by a 0 to
CTRLB[3]. This initiates a new data rate measurement. Follow
Step 2 through Step 4 to read back the new data rate.
1. Write a 1 to CTRLA[1]. This enables the fine data rate
measurement capability of the ADN2814. This bit is level
sensitive and does not need to be reset to perform
subsequent frequency measurements.
Note that a data rate readback is valid only if LOL is low. If LOL
is high, the data rate readback is invalid.
Additional Features Available via the I
2
C Interface
Coarse Data Rate Readback
2. Reset MISC[2] by writing a 1 followed by a 0 to CTRLB[3].
This initiates a new data rate measurement.
The data rate can be read back over the I
2
C interface to
approximately ±10% without the need of an external reference
clock. A 9-bit register, COARSE_RD[8:0], can be read back
when LOL is deasserted. The eight MSBs of this register are the
contents of the RATE[7:0] register. The LSB of the COARSE_RD
register is Bit MISC[0].
3. Read back MISC[2]. If it is 0, the measurement is not
complete. If it is 1, the measurement is complete and the
data rate can be read back on FREQ[22:0]. The time for a
data rate measurement is typically 80 ms.
4. Read back the data rate from FREQ2[6:0], FREQ1[7:0], and
FREQ0[7:0].
Tabl e 13 provides coarse data rate readback to within ±10%.
LOS Configuration
The data rate can be determined by
The LOS detector output, Pin 22, can be configured to be either
active high or active low. If CTRLC[2] is set to Logic 0 (default),
the LOS pin is active high when a loss-of-signal condition is
detected. Writing a 1 to CTRLC[2] configures the LOS pin to be
active low when a loss-of-signal condition is detected.
[]
()
)_(
/..
RATESEL
REFCLK
DATARATE
fFREQf
+
×=
14
2022
where:
FREQ[22:0] is the reading from FREQ2[6:0] (MSByte),
FREQ1[7:0], and FREQ0[7:0] (LSByte).
System Reset
f
DATARATE
is the data rate (Mb/s).
A frequency acquisition can be initiated by writing a 1 followed
by a 0 to the I
2
C Register Bit CTRLB[5]. This initiates a new
frequency acquisition while keeping the ADN2814 in the
operating mode that it was previously programmed to in
Registers CTRL[A], CTRL[B], and CTRL[C].
f
REFCLK
is the REFCLK frequency (MHz).
SEL_RATE is the setting from CTRLA[7:6].
Table 12.
D22 D21...D17 D16 D15 D14...D9 D8 D7 D6...D1 D0
FREQ2[6:0] FREQ1[7:0] FREQ0[7:0]