Power-on reset (POR) is the reset that occurs when a valid supply voltage is first applied. The POR process requires t_POR from when the supply voltages reach 90% of their nominal value. Internal circuitry powers up and the registers are set to their default state during this time. The DRDY pin transitions from low to high immediately after t_POR indicating the SPI interface is ready for communication. The device ignores any SPI communication before this point.