3. Clock Inputs
The Si5386 supports four inputs that can be used as inputs to the DSPLL.
3.1 Input Source Selection
The inputs accept ac-coupled clocks that are differential or singled ended such as LVCMOS. In addition, the inputs also accept
dc-coupled CMOS type inputs with 50% or very low input duty cycle. Input selection can be manual (pin or register controlled) or
automatic with user definable priorities. There is a register to select pin or register control, and to configure the input as shown below.
Table 3.1. Input Selection Configuration
Register Name
Hex Address [Bit Field]
Function
CLK_SWITCH_MODE
0x0536[1:0]
Selects manual or automatic switching modes. Automatic mode can be rever-
tive or non-revertive. Selections are the following:
00 Manual,01 Automatic non-revertive
02 Automatic revertive, 03 Reserved
IN_SEL_REGCTRL
0x052A [0]
0 for pin controlled clock selection
1 for register controlled clock selection
IN_SEL
0x052A [2:1]
0 for IN0, 1 for IN1,
2 for IN2, 3 for IN3 (or FB_IN)
3.1.1 Manual Input Switching
In manual mode, CLK_SWITCH_MODE=0x00.
Input switching can be done manually using the IN_SEL[1:0] device pins from the package or through register 0x052A IN_SEL[2:1]. Bit
0 of register 0x052A determines if the input selection is pin selectable or register selectable. The default is pin selectable. The following
table describes the input selection on the pins. Note that when Zero Delay Mode is enabled, the FB_IN pins will become the feedback
input and IN3 therefore is not available as a clock input. Note, in Zero Delay Mode, register based input clock selection must be done
with IN_SEL (0x052A). If there is no clock signal on the selected input, the device will automatically enter free-run or holdover mode.
Table 3.2. Manual Input Selection using IN_SEL[1:0] Pins
IN_SEL[1:0] DEVICE PINS
Zero Delay Mode Disabled
Zero Delay Mode Enabled
00
IN0
IN0
01
IN1
IN1
10
IN2
IN2
11
IN3
Reserved
Si5386 Rev. E Reference Manual • Clock Inputs
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