mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 543

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

The Verify Backdoor Access Key command is monitored by the FTFL and an illegal key
prohibits future use of the Verify Backdoor Access Key command. A reset of the MCU 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 MCU 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 MCU, the security state of the FTFL 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 MCU has full control of the
contents of the Flash Configuration Field. The MCU 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.
23.4.13 Reset Sequence
On each system reset the FTFL module executes a sequence which establishes initial
values for the flash block configuration parameters, FPROT, FDPROT, FEPROT, FOPT,
and FSEC registers and the FCNFG[RAMRDY, EEERDY] bits.
CCIF is cleared throughout the reset sequence. The FTFL module holds off all CPU
access for a portion of 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 FTFL 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.
Freescale Semiconductor, Inc.
1. Follow the command sequence for the Verify Backdoor Access Key command as
2. If the Verify Backdoor Access Key command is successful, the MCU is unsecured
explained in
and the FSEC[SEC] bits are forced to the unsecure state
Verify Backdoor Access Key Command
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Preliminary
(Flash Configuration Field
Chapter 23 Flash Memory Module (FTFL)
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