Flash security features are discussed further in
AN4507: Using the Kinetis Security and
. Note that not all features described in the application note are
available on this device.
Table 29-70. FSEC register fields
FSEC field
Description
KEYEN
Backdoor Key Access
MEEN
Mass Erase Capability
FSLACC
Freescale Factory Access
SEC
MCU security
29.4.12.1 Flash Memory Access by Mode and Security
The following table summarizes how access to the flash memory module is affected by
security and operating mode.
Table 29-71. Flash Memory Access Summary
Operating Mode
Chip Security State
Unsecure
Secure
NVM Normal
Full command set
NVM Special
Full command set
Only the Erase All Blocks and Read 1s All
Blocks commands.
29.4.12.2 Changing the Security State
The security state out of reset can be permanently changed by programming the security
byte of the flash configuration field. This assumes that you are starting from a mode
where the necessary program flash erase and program commands are available and that
the region of the program flash containing the flash configuration field is unprotected. If
the flash security byte is successfully programmed, its new value takes affect after the
next chip reset.
29.4.12.2.1 Unsecuring the Chip Using Backdoor Key Access
The chip can be unsecured by using the backdoor key access feature, which requires
knowledge of the contents of the 8-byte backdoor key value stored in the Flash
Configuration Field (see
Flash Configuration Field Description
bits are in the enabled state, the Verify Backdoor Access Key command (see
Functional Description
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
654
Freescale Semiconductor, Inc.