si5315 Silicon Laboratories, si5315 Datasheet - Page 33

• Manufacturer Part Number: si5315
• Description: Synchronous Ethernet/telecom Jitter Attenuating Clock Multiplier
• Manufacturer: Silicon Laboratories

4.3.2. Automatic Clock Selection
The AUTOSEL input pin sets the input clock selection mode as shown in Table 9. Automatic switching is either
revertive or non-revertive. Setting AUTOSEL to M or H, changes the CS_CA pin to an output pin that indicates the
state of the automatic clock selection.
The prioritization of clock inputs for automatic switching is shown in Table 12. This priority is hardwired in the
devices.
At power-on or reset, the valid CKINn with the highest priority (1 being the highest priority) is automatically
selected. If no valid CKINn is available, the device suppresses the output clocks and waits for a valid CKINn signal.
If the currently selected CKINn goes into an alarm state, the next valid CKINn in priority order is selected. If no valid
CKINn is available, the device enters holdover.
Operation in revertive and non- revertive is different when a signal becomes valid:
Revertive (AUTOSEL = H):
Non-revertive (AUTOSEL = M): The active clock does not change until there is an alarm on the active clock. The
CS_CA
Table 10. Manual Input Clock Selection, AUTOSEL = L
Table 11. Clock Active Indicators, AUTOSEL = M or H
0
1
Table 12. Input Clock Priority for Auto Switching
CS_CA
The device constantly monitors all CKINn. If a CKINn with a higher priority than
the current active CKINn becomes valid, the active CKINn is changed to the
CKINn with the highest priority.
device will then select the highest priority CKINn that is valid. Once in holdover,
the device will switch to the first CKINn that becomes valid.
0
1
Priority
1
2
3
Preliminary Rev. 0.2
Active Clock
CKIN1
CKIN2
AUTOSEL = L
Input Clocks
Si5315
CKIN1
CKIN2
Holdover
CKIN1
CKIN2
Si5315
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