GS6151 datasheet(18/77 Pages) SEMTECH

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GS6151

Final Data Sheet

Rev.4

PDS-060389

August 2015

18 of 77

Semtech

Proprietary & Confidential

www.semtech.com

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 2h. 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

10h. The LOS threshold hysteresis can be set by the LOS_HYSTERESIS bits in the

LOS_CONTROL_REG_0 register at address Fh.

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 4Fh, and as a sticky status through the LOS_STICKY bit in the STICKY_STATUS

The corresponding GPIO pin will be LOW (signal present) when the input signal

amplitude within a predefined window is above the defined threshold.

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