18.3.2.3.2 Custom Calibration

This mode is a two-step procedure:

  1. The user provides a direct calibration using values in DDR3PHY_ZQ0CR1.ZPROG and records the impedance control results from DDR3PHY_ZQ0SR0.ZCTRL.
  2. The user applies the correction factor that provides the custom impedance.

The following example program driver output impedance to 18 ohms.

  1. The user performs a direct calibration for driver Zo=34 ohms. Assume the result in DDR3PHY_ZQ0SR0.ZCTRL shows that the driver pull-up index is 12, and the driver pull-down index is 13.
  2. Calculate and apply the override data for 18 ohm impedance adjustment by writing fields ZDEN=1 and ZDATA as follows::
(<cal_value/<req_value>) * <cal_index>
Driver pull-down    (36/18) * 13 = 26
Driver pull-up      (36/18) * 12 = 24
Note: The resulting index from the previous example must be smaller than 31 according to the allowable range of the hardware support.