GS12281 datasheet(39/97 Pages) SEMTECH

39 / 97 page

GS12281

Final Data Sheet

Rev.9

PDS-061385

February 2019

39 of 97

Semtech

Proprietary & Confidential

www.semtech.com

4.7.1 Bypassed Re-timer Signal Output Control

With the default power-up settings, the GS12281 outputs will automatically switch to

the bypassed signal (non-re-timed) whenever the PLL is unlocked. Alternatively, manual

re-timer bypass may be configured by setting the CTRL_OUTPUT<n>_RETIMER_

AUTO_BYPASS and CTRL_OUTPUT<n>_RETIMER_MANUAL_BYPASS parameters in

remain bypassed for all rates.

The re-timer bypass function, manual or automatic, does not affect the input

equalization function of the device.

If both outputs are manually disabled, then the device will power down the CDR block

and features of the re-timer such as rate detect and lock detect will no longer be

accessible in this mode.

4.7.2 Output Driver Polarity Inversion

While in data mode, the signal polarity may be inverted at the outputs through the

CTRL_OUTPUT<n>_ DATA_ INVERT parameters in register 0x48. This may be useful to

compensate for an inverted upstream signal or to facilitate board signal routing. To

invert the polarity of either of the two output drivers, write 1b to control parameter

CTRL_OUTPUT<n>_DATA_ INVERT.

4.7.3 Output Driver Data Rate Selection

By default, the GS12281 uses the output driver and slew rate group settings for the data

rate to which the CDR is locked.

When the CDR is unlocked it will use the 6G/12G rate group:

 CFG_OUTPUT<n>_CD_UHD_DRIVER_SWING

 CFG_OUTPUT<n>_CD_UHD_PREEMPH_WIDTH

 CFG_OUTPUT<n>_CD_UHD_PREEMPH_AMPL

 CFG_OUTPUT<n>_CD_UHD_PREEMPH_PWRDWN

If required, manual selection of the output driver and slew rate group is possible using

the following steps:

1. Set CTRL_OUTPUT<n>_AUTO_SLEW = 0

2. Set CTRL_OUTPUT<n>_MANUAL_SLEW to the desired rate group. The slew rate

options are as follows:

0 = SD/MADI

1 = HD/3G

2 = 6G/12G

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