For LPC4300 series microcontrollers with or without on-chip flash memory, the boot loader can allow the device to start from external serial flash through the SPIFI interface. The diagram shown on this slide details the boot-flow steps of the quad SPI flash boot mode. Booting into serial flash occurs only if the mode pins are set accordingly per each device specification. The default SPIFI clock is 32 MHz. Since the CPU can run at a higher frequency, the serial clock is divided down from the PLL automatically. When the RDID command detects a recognized device, the boot loader automatically configures SPIFI for the highest available data rate. If the detected device is unknown, the SPIFI clock is reduced to 18 MHz.