DDR4 EMIF VREF pins, Arria 10

Hi Ju-Ti,

"Question 1: could this non-zero VREF voltage have effect on calibration?"

• It's may and may not affect calibration process since it's supply to voltage source not to GND. As you can see, the calibration can pass after changing some parameters.
• But it's better to follow the guideline to avoid any conflict in the functionality.

"Question 2: Is it possible that Address/Command phase of calibration is disturbed due to this, and causes later rd/wr data deskewing to fail? "

• It's may not affect the calibration process because I think the alert_n is not used during the calibration.
• Besides, the alert_n signal has been terminated.
• I would say that this might not be the root cause but you can follow the recommendation for the new board.

Regards,

Adzim