Si5345-44-42-D-RM
Rev. 1.0
27
5.3.1. Input Loss of Signal (LOS) Fault Detection
The loss of signal monitor measures the period of each input clock cycle to detect phase irregularities or missing
clock edges. Each of the input LOS circuits has its own programmable sensitivity which allows ignoring missing
edges or intermittent errors. Loss of signal sensitivity is configurable using the ClockBuilder Pro utility. The LOS
status for each of the monitors is accessible by reading a status register. The live LOS register always displays the
current LOS state and a sticky register when set, always stays asserted until cleared by the user.
Figure 10. LOS Status Indicators
A LOS monitor is also available to ensure that the external crystal or reference clock is valid. By default the output
clocks are disabled when LOSXAXB is detected. This feature can be disabled such that the device will continue to
produce output clocks even when LOSXAXB is detected. Single-ended inputs must be connected to the XA input
pin with the XB pin terminated properly for LOSXAXB to function correctly. The table below lists the loss of signal
status indicators and fault monitoring control registers.
Table 14. Loss of Signal Status Monitoring and Control Registers
Register Name
Hex
Address
[Bit Field]
Function
LOS
0x000D[3:0] LOS status monitor for IN3 (bit3), IN2 (bit2), IN1(bit1), IN0 (bit0) indicates if a
valid clock is detected. A set bit indicates the input is LOS.
SYSINCAL
0x000C[0]
Asserted when in calibration
LOSXAXB
0x000C[1]
LOS status monitor for the STAL or REFCLK at the XA/XB pins
LOS_FLG
0x0012[3:0] LOS status monitor sticky bits for IN3, IN2, IN1, IN0. Sticky bits will remain
asserted when a LOS event occurs until manually cleared. Writing zero to the
bit will clear it.
SYSINCAL_FLG
0x0011[0]
SYSINCAL sticky bit. Sticky bits will remain asserted until written with a zero to
clear.
LOSXAXB_FLG
0x0011[1]
LOS status monitor sticky bits for XAXB. Sticky bits will remain asserted when
a LOS event occurs until cleared. Writing zero to the bit will clear it.
LOS_EN
0x002C[3:0] LOS monitor enable for IN3, IN2, IN1, IN0. Allows disabling the monitor if
unused.
0: Disable LOS Detection
1: Enable LOS Detection (default)
LOSXAXB_DIS
0x002C[4] Enable LOS detection on the XAXB inputs.
0: Enable LOS Detection (default)
1: Disable LOS Detection
LOS
en
Monitor
LOS
LOS
Sticky
Live