Table 29-38. FSEC register fields
FSEC field Description
KEYEN Backdoor Key Access
MEEN Mass Erase Capability
FSLACC Factory Security Level 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 29-39. 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). If the FSEC[KEYEN]
bits are in the enabled state, the Verify Backdoor Access Key command (see Verify
Backdoor Access Key Command) can be run; it allows the user to present prospective
keys for comparison to the stored keys. If the keys match, the FSEC[SEC] bits are
changed to unsecure the chip. The entire 8-byte key cannot be all 0s or all 1s; that is,
0000_0000_0000_0000h and FFFF_FFFF_FFFF_FFFFh are not accepted by the Verify
Functional Description
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
678 NXP Semiconductors
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