Reset Sequence - NXP Semiconductors freescale KV4 Series Reference Manual

Functional Description
1. Follow the command sequence for the Verify Backdoor Access Key command as
explained in Verify Backdoor Access Key Command
2. If the Verify Backdoor Access Key command is successful, the chip is unsecured and
the FSEC[SEC] bits are forced to the unsecure state
An illegal key provided to the Verify Backdoor Access Key command prohibits further
use of the Verify Backdoor Access Key command. A reset of the chip is the only method
to re-enable the Verify Backdoor Access Key command when a comparison fails.
After the backdoor keys have been correctly matched, the chip is unsecured by changing
the FSEC[SEC] bits. A successful execution of the Verify Backdoor Access Key
command changes the security in the FSEC register only. It does not alter the security
byte or the keys stored in the Flash Configuration Field
Description). After the next reset of the chip, the security state of the flash memory
module reverts back to the flash security byte in the Flash Configuration Field. The
Verify Backdoor Access Key command sequence has no effect on the program and erase
protections defined in the program flash protection registers.
If the backdoor keys successfully match, the unsecured chip has full control of the
contents of the Flash Configuration Field. The chip may erase the sector containing the
Flash Configuration Field and reprogram the flash security byte to the unsecure state and
change the backdoor keys to any desired value.

32.4.12 Reset Sequence

On each system reset the flash memory module executes a sequence which establishes
initial values for the flash block configuration parameters, FPROT, FOPT, FSEC,
FXACC, FSACC, and FACNFG registers.
FSTAT[CCIF] is cleared throughout the reset sequence. The flash memory module holds
off CPU access during the reset sequence. Flash reads are possible when the hold is
removed. Completion of the reset sequence is marked by setting CCIF which enables
flash user commands.
If a reset occurs while any flash command is in progress, that command is immediately
aborted. The state of the word being programmed or the sector/block being erased is not
guaranteed. Commands and operations do not automatically resume after exiting reset.
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KV4x Reference Manual, Rev. 2, 02/2015
Preliminary
(Flash Configuration Field
Freescale Semiconductor, Inc.