Information
FCCOB match those stored in the Backdoor Comparison Key bytes of the Flash
Configuration Field (see Flash Configuration Field Description). The column labelled
Flash Configuration Field offset address shows the location of the matching byte in the
Flash Configuration Field.
Table 28-62. Verify Backdoor Access Key Command FCCOB Requirements
FCCOB Number FCCOB Contents [7:0] Flash Configuration Field Offset Address
0 0x45 (VFYKEY)
1-3 Not Used
4 Key Byte 0 0x0_0000
5 Key Byte 1 0x0_0001
6 Key Byte 2 0x0_0002
7 Key Byte 3 0x0_0003
8 Key Byte 4 0x0_0004
9 Key Byte 5 0x0_0005
A Key Byte 6 0x0_0006
B Key Byte 7 0x0_0007
After clearing CCIF to launch the Verify Backdoor Access Key command, the flash
memory module checks the FSEC[KEYEN] bits to verify that this command is enabled.
If not enabled, the flash memory module sets the FSTAT[ACCERR] bit and terminates.
If the command is enabled, the flash memory module compares the key provided in
FCCOB to the backdoor comparison key in the Flash Configuration Field. If the
backdoor keys match, the FSEC[SEC] field is changed to the unsecure state and security
is released. If the backdoor keys do not match, security is not released and all future
attempts to execute the Verify Backdoor Access Key command are immediately aborted
and the FSTAT[ACCERR] bit is (again) set to 1 until a reset of the flash memory module
module occurs. If the entire 8-byte key is all zeros or all ones, the Verify Backdoor
Access Key command fails with an access error. The CCIF flag is set after the Verify
Backdoor Access Key operation completes.
Table 28-63. Verify Backdoor Access Key Command Error Handling
Error Condition Error Bit
The supplied key is all-0s or all-Fs FSTAT[ACCERR]
An incorrect backdoor key is supplied FSTAT[ACCERR]
Backdoor key access has not been enabled (see the description of the FSEC register) FSTAT[ACCERR]
This command is launched and the backdoor key has mismatched since the last power down
reset
FSTAT[ACCERR]
Chapter 28 Flash Memory Module (FTFL)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 551