• The BOOTCFG0 pin is asserted. The pin must be configured as BOOTCFG0 bysetting the BOOTPIN_OPT bit of FOPT to 0.• A user applications running on flash or RAM calls into the Kinetis Bootloader entrypoint address in ROM, to start Kinetis Bootloader execution.The FOPT[BOOTSRC_SEL] determines the boot source. The FOPT register is located inthe flash configuration field at address 0x40D in the flash memory array. For a completelist of options, see the Boot options section in the Reset and Boot chapter. If FOPT [7] isset to 1, then the device will boot to ROM out of reset. Flash memory defaults to all 1swhen erased, so a blank chip will automatically boot to ROM.The BOOTCFG0 pin is shared with the NMI pin, with NMI being the default usage.Regardless of whether the NMI pin is enabled or not, the NMI functionality is disabled ifthe ROM is executed out of reset, for as long as the ROM is running.When the ROM is executed out of reset, vector fetches from the CPU are redirected tothe ROM's vector table in ROM memory at offset 0x1C00_0000. This ensures that anyexceptions will be handled by the ROM.After the Kinetis Bootloader has started, the following procedure starts bootloaderoperations:1. The RCM_MR [FORCEROM] bits are set, so that the device will reboot back intothe ROM if/when the device is reset.2. Initializes the bootloader's .data and .bss sections.3. Reads bootloader configuration data from flash at address 0x3C0. The configurationdata is only used if the tag field is set to the expected 'kcfg' value. If the tag isincorrect, then the configuration values are set to default, as if the data was all 0xFFbytes.4. Clocks are configured. See the Clock Configuration section.5. Enabled peripherals are initialized.6. The bootloader waits for communication to begin on a peripheral.• If detection times out, then the bootloader jumps to the user application in flash.See Bootloader Exit state section.• If communication is detected, then all inactive peripherals are shut down, and thecommand phase is entered.NOTEThe flash sector containing the vector table should not belocated in the execute-only region, because the Kinetisbootloader cannot read the PC and SP addresses in anexecute-only region.Functional DescriptionKL27 Sub-Family Reference Manual , Rev. 5, 01/2016178 Freescale Semiconductor, Inc.
