Intel® MAX® 10 General Purpose I/O User Guide

ID 683751
Date 1/27/2022
Public

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2.4.3.1. OCT Calibration

The OCT calibration circuit compares the total impedance of the output buffer to the external resistors connected to the RUP and RDN pins. The circuit dynamically adjusts the output buffer impedance until it matches the external resisters.

Each calibration block comes with a pair of RUP and RDN pins.

During calibration, the RUP and RDN pins are each connected through an external 25 Ω, 34 Ω, 40 Ω, 48 Ω, or 50 Ω resistor for respective on-chip series termination value of 25 Ω, 34 Ω, 40 Ω, 48 Ω, and 50 Ω:

  • RUP—connected to VCCIO.
  • RDN—connected to GND.

The OCT calibration circuit compares the external resistors to the internal resistance using comparators. The OCT calibration block uses the comparators' output to dynamically adjust buffer impedance.

During calibration, the resistance of the RUP and RDN pins varies. To estimate of the maximum possible current through the external calibration resistors, assume a minimum resistance of 0 Ω on the RUP and RDN pins.