18.3.2.3 Impedance Calibration

The DDR3PHY calibrates driver output impedance and ODT impedance.

Only an external precision resistor (240 ohms/1%) is required. All other necessary circuitry is implemented in the DDR3PHY.

The four impedance elements (output impedance pull-down/up and ODT pull-down/up) are calibrated sequentially.

There are two modes of operation:

Direct calibration – uses DDR3PHY_ZQ0CR1.ZPROG settings
Custom calibration – extends calibration beyond the values available on DDR3PHY_ZQ0CR1.ZPROG

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