zl50021 Zarlink Semiconductor, zl50021 Datasheet - Page 43

• Manufacturer Part Number: zl50021
• Description: Enhanced 4 K Digital Switch With Stratum 3 Dpll
• Manufacturer: Zarlink Semiconductor

With a preferred reference, if more than two references are required, or the two references are not in consecutive
order, or the roles of the two references need to be interchanged, then external software is required to manually
control the reference switching of the DPLL (by monitoring the reference failure status and reprogramming the
device accordingly).
12.1.4
In freerun mode, the DPLL generates a fixed output frequency based on the crystal oscillator and a programmed
centre frequency. To meet Stratum 3, the accuracy of the circuitry for the freerunning output clock must be 4.6 ppm
or better. The circuit’s freerun accuracy is better than 0.003 ppm.
In freerun mode, the DPLL does not lock to any reference. It is important that the device is not simultaneously in
freerun mode (see the RCCR Register) and fast lock mode (see the BWCR Register). Otherwise, the output frame
pulse may not be generated correctly.
12.1.4.1
When the DPLL is in the freerun mode, it can be put into software controlled mode by enabling the SWE (bit 3) in
the DPLL Control Register (DPLLCR). The Software Delta Frequency Register (SWDFR) contains the frequency
offset to which the DPLL outputs will move. If SWF (bit 4) in the DPLL Control Register (DPLLCR) is low, the DPLL
outputs will gradually move to the given frequency offset, with the speed defined by the DPLL internal filter and
phase alignment speed (phase slope) limiter. If SWF (bit 4) is high, the DPLL outputs will reach the Software Delta
Frequency Register (SWDFR) frequency offset immediately after it is written, allowing an external software-based
filter and phase alignment speed (phase slope) limiter to be used. When SWE (bit 3) is low or the DPLL is not in the
freerun mode, the value of Software Delta Frequency Register (SWDFR) will be ignored. For detailed description of
the DPLL Control Register (DPLLCR) bits and the Software Delta Frequency Register (SWDFR) bits see Table 29
on page 66, and Table 33 on page 71, respectively.
12.1.5
DPLL_IRM (bit 0) in the DPLL Control Register (DPLLCR) enables the internal reset mode. In the internal reset
mode, the DPLL module is disabled to save power. The circuit will be reset continuously and no output clocks will
be generated. When the internal DPLL module is in the internal reset mode, all registers remain accessible. Note
that applying the DPLL reset does not reset the DPLL registers: they preserve the values that they had prior to
entering reset.
13.0
13.1
The DPLL is capable of synchronizing to one of the following input frequencies:
Input Frequencies
DPLL Frequency Behaviour
Freerun Mode
DPLL Internal Reset Mode
Software Controlled Mode
Table 9 - DPLL Input Reference Frequencies
Zarlink Semiconductor Inc.
1.544 MHz (DS1)
2.048 MHz (E1)
ZL50021
16.384 MHz
4.096 MHz
8.192 MHz
19.44 MHz
8 kHz
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Data Sheet