NXP Semiconductors K32 L2A Series, Reference Manual, Page: 253 / 1379

The first configuration field 'tag' is a tag value or magic number. The tag value must be
set to 'kcfg' for the bootloader configuration data to be recognized as valid. If tag-field
verification fails, then the Kinetis Bootloader assumes that the flash is not initialized and
uses a predefined default configuration (all as 0xFF). The tag value is treated as a
character string, so bytes 0-3 must be set as shown in the table.
Table 14-4. tag Configuration Field
Offset tag Byte Value
0 'k' (0x6B)
1 'c' (0x63)
2 'f' (0x66)
3 'g' (0x67)
The flags in the clockFlags configuration field are enabled if the corresponding bit is
cleared (0).
Table 14-5. clockFlags Configuration Field
Bit Flag Description
0 HighSpeed Enable high speed mode (i.e., 48 MHz). Read Clock Configuration
section for more information on the high speed mode.
1 - 7 Reserved
14.3.3 Start-up Process
Any of the following conditions will force the hardware to start the Kinetis Bootloader:
• FOPT [7] is set to 1. This forces the ROM to run out of reset.
• The BOOTCFG0 pin is asserted. The pin must be configured as BOOTCFG0 by
setting the BOOTPIN_OPT bit of FOPT to 0.
• A user applications running on flash or RAM calls into the Kinetis Bootloader entry
point address in ROM, to start Kinetis Bootloader execution.
The FOPT[BOOTSRC_SEL] determines the boot source. The FOPT register is located in
the flash configuration field at address 0x40D in the flash memory array. For a complete
list of options, see the Boot options section in the Reset and Boot chapter. If FOPT [7] is
set to 1, then the device will boot to ROM out of reset. Flash memory defaults to all 1s
when 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 if
the ROM is executed out of reset, for as long as the ROM is running.
Chapter 14 Kinetis ROM Bootloader
K32 L2A Reference Manual, Rev. 2, 01/2020
NXP Semiconductors 253