Stratix V Device Handbook: Volume 2: Transceivers

ID 683779
Date 11/23/2021
Document Table of Contents Automatic Lock Mode

In automatic lock mode, the CDR initially locks to the input reference clock (LTR mode). After the CDR locks to the input reference clock, the CDR locks to the incoming serial data (LTD mode) when the following conditions are met:

  • The signal threshold detection circuitry indicates the presence of valid signal levels at the receiver input buffer.
  • The CDR output clock is within the configured ppm frequency threshold setting with respect to the input reference clock (frequency locked).
  • The CDR output clock and the input reference clock are phase matched within approximately 0.08 unit interval (UI) (phase locked).

If the CDR does not stay locked to data because of frequency drift or severe amplitude attenuation, the CDR switches back to LTR mode.