ZL30402/QCC ZARLINK [Zarlink Semiconductor Inc], ZL30402/QCC Datasheet - Page 28

• Manufacturer Part Number: ZL30402/QCC
• Description: SONET/SDH Network Element PLL
• Manufacturer: ZARLINK [Zarlink Semiconductor Inc]

5.1.4
The NORMAL to HOLDOVER to NORMAL mode switching is usually performed when:
•
•
Two types of transitions are possible:
•
•
In both cases, the change of references provides “hitless” switching.
5.2
The Master Crystal Oscillator and its programmable Master Clock Frequency Calibration register (see Table 18,
Table 19, Table 20, and Table 21) have been described in Section 3.0 "Master Clock Frequency Calibration Circuit",
on page 13. Programming of this register should be done after system has been powered long enough for the
Master Crystal Oscillator to reach a steady operating temperature. When the temperature stabilizes the crystal
oscillator frequency should be measured with an accurate frequency meter. The frequency measurement should be
substituted for the f
where f
A reference clock is available but its frequency drifts beyond some specified limit. In a Network Element with
stratum 3 internal clocks, the reference failure is declared when its frequency drifts more than ±12 ppm
beyond its nominal frequency.
During routine maintenance of equipment when orderly switching of reference clocks is possible. This may
happen when synchronization references must be rearranged or when a faulty line card must be replaced.
Semi-automatic transition, which involves changing RefSel input to select a secondary reference clock
without changing the mode select inputs MS2, MS1 = 00 (Normal mode). This forces ZL30402 to
momentarily transition through the Holdover state and automatically return to Normal mode after
synchronizing to a secondary reference clock.
Manual transition, which involves switching into Holdover mode (MS2, MS1 = 01), changing references with
RefSel, and manual return to the Normal mode (MS2, MS1 = 00).
MCFC = 45036 * ( - f
Programming Master Clock Oscillator Frequency Calibration Register
offset
RESET
Reference Switching (RefSel): NORMAL --> HOLDOVER --> NORMAL
RESET == 1
is the crystal oscillator frequency offset from the nominal 20 000 000 Hz frequency expressed in Hz.
unconditional return from
MS2, MS1 == 10 forces
any state to Free-run
offset
FREE-
variable in the following equation.
RUN
10
offset
MS2, MS1! = 10
)
MS2, MS1 == 01 OR
RefSel change
Figure 10 - Manual Reference Switching
HOLD-
OVER
01
Zarlink Semiconductor Inc.
MS2, MS1 == 00
ZL30402
Ref: OK &
{AUTO}
28
RefSel Change
(LOCKED)
NORMAL
00
Ref: OK --> FAIL &
MS2, MS1 == 00
{AUTO}
HOLD-
OVER
AUTO
MS2, MS1 == 00 &
MHR= 0-->1 then 1-->0
{MANUAL}
Ref: FAIL --> OK &
AHRD=0
{AUTO}
MS2, MS1 == 00 &
Ref: FAIL --> OK &
AHRD=1 &
Data Sheet