The power-on reset (POR) generator initializes the system when the VDD supply voltage is above the power-on threshold. This also applies in high voltage mode, where the VDD supply voltage is provided by the high voltage regulator (VREGH).
The system is held in a reset state until the supply has reached the minimum operating voltage, and the internal voltage regulators have started. After a power-on reset, the application core is started while the network core is held in reset, see Network Force-OFF.