GS6151 Datasheet, PDF (18/77 Pages) Semtech Corporation – Multi-Rate 6G UHD-SDI

4.2 Reference Clock
The GS6151 can operate with or without an external frequency reference. For
applications requiring rapid asynchronous locking, a 27MHz reference or crystal is
required.
The PLL lock times for both referenceless and external crystal reference operation are
given in Table 2-3: AC Electrical Characteristics.
If a reference is connected to the XTAL_CLK_IN pin or a crystal is connected to the
XTAL_CLK_IN and XTAL_CLK_OUT pins of the device, it will automatically be used as the
reference frequency for rapid asynchronous lock. If XTAL_CLK_IN is not connected to a
crystal, XTAL_CLK_OUT must be left unconnected.
The XTAL_CLK_IN pin operates correctly when connected directly to the
XTAL_BUF_OUT from another GS6151, or a 27MHz output of a different device.
4.3 Signal Monitoring
The GS6151 measures and reports the following signal status and quality monitoring
parameters:
• Loss of Signal
• Lock Detection
• Rate Detection
• Low/High Bit Rate Detection
4.3.1 Loss of Signal Detection
LOS (Loss of Signal) detection is an active HIGH output available to the application on
either of the GPIO0 or GPIO1 multi-function status and control pins. It is selected for
output using the GPIO[0:1]_IO_SELECT and GPIO[0:1]_SELECT bits accessible in the
GPIO_CONTROL_REG_0 register at address 2_h. It is the default output of the GPIO0 pin.
LOS indicates when the serial digital signal selected by the input selector is invalid. This
function is always active.
The corresponding GPIO pin will be HIGH (signal lost) when the input signal amplitude
within a predefined window falls below the threshold set by the bits
DDI[0:1]_LOS_THRESHOLD_CONTROL in the LOS_CONTROL_REG_1 register at address
10_h. The LOS threshold hysteresis can be set by the LOS_HYSTERESIS bits in the
LOS_CONTROL_REG_0 register at address F_h.
The corresponding GPIO pin will be LOW (signal present) when the input signal
amplitude within a predefined window is above the defined threshold.
The LOS status is also available through the LOS bit in the PLL_STATUS register at
address 4F_h, and as a sticky status through the LOS_STICKY bit in the STICKY_STATUS
register at address 50_h.
The corresponding GPIO pin will be LOW (signal present) when the input signal
amplitude within a predefined window is above the defined threshold.
GS6151
Final Data Sheet
PDS-060389
Rev.4
August 2015
www.semtech.com
18 of 77
Semtech
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