3.1.2 Automatic Input Switching
In automatic mode CLK_SWITCH_MODE = 0x01 (non-revertive) or 0x02 (revertive)
An automatic input switch is available in addition to the above mentioned manual switching option described in
. In automatic mode, the selection criteria is based on input clock qualification, input priority and the revertive option. The
IN_SEL[1:0] pins or IN_SEL[2:1] register bits are not used in automatic input selection. Also, only input clocks that are valid (i.e., with
no active alarms) can be selected by the automatic clock selection. If there are no valid input clocks available the DSPLL will enter the
holdover mode. With revertive switching enabled, the highest priority input with a valid input clock is always selected. If an input with a
higher priority becomes valid then an automatic switchover to that input will be initiated. With non-revertive switching, the active input
will always remain selected while it is valid. If it becomes invalid an automatic switchover to a valid input with the highest priority will be
initiated.
Table 3.3. Registers for Automatic Input Selection
Register Name
Hex Address [Bit
Field]
Function
CLK_SWITCH_MODE
0x0536[1:0]
Selects manual or automatic switching modes. Automatic mode can be revertive
or non-revertive. Selections are the following: 00 Manual,01 Automatic non-rever-
tive 02 Automatic revertive, 03 Reserved
ZDM_EN
0x0487[0]
0: disable zero delay mode
1: enable zero delay mode
ZDM_AUTOSW_EN
0x0487[4]
0: automatic switching disabled for zero-delay mode
1: automatic input switching enabled and input clock selection governed by auto-
matic input switching engine
IN0_PRIORITY
0x0538[2:0]
IN0, IN1, IN2, IN3 priority select for the automatic selection state machine. Priority
selections are 1,2,3,4, or zero for not selected.
IN1_PRIORITY
0x0538[6:4]
IN2_PRIORITY
0x0539[2:0]
IN3_PRIORITY
0x0539[6:4]
IN_LOS_MSK
0x0537[3:0]
Determines the LOS status for IN3,2,1,0 and is used in determining a valid clock
for automatic input selection
0 to use LOS in clock selection logic, 1 to mask LOS from the clock selection logic
IN_OOF_MSK
0x0537[7:4]
Determines the OOF status for IN3,2,1,0 and is used in determining a valid clock
for the automatic input selection
0 to use OOF in the clock selection logic, 1 to mask the OOF from the clock
selection logic
When in zero delay mode (ZDM_EN (0x0487[0]) the phase difference between the output, which is connected to the selected input, will
be nulled to zero. However the IO delay variation will substantially increase in ZDM mode if the Fpfd is below 128 kHz. Phase buildout
is not supported in Zero Delay Mode.
Si5386 Rev. E Reference Manual • Clock Inputs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
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