27.4.10.10 Verify Backdoor Access Key CommandThe Verify Backdoor Access Key command only executes if the mode and securityconditions are satisfied (see Flash Commands by Mode). Execution of the VerifyBackdoor Access Key command is further qualified by the FSEC[KEYEN] bits. TheVerify Backdoor Access Key command releases security if user-supplied keys in theFCCOB match those stored in the Backdoor Comparison Key bytes of the FlashConfiguration Field (see Flash Configuration Field Description). The column labelledFlash Configuration Field offset address shows the location of the matching byte in theFlash Configuration Field.Table 27-48. Verify Backdoor Access Key Command FCCOB RequirementsFCCOB Number FCCOB Contents [7:0] Flash Configuration Field Offset Address0 0x45 (VFYKEY)1-3 Not Used4 Key Byte 0 0x0_00005 Key Byte 1 0x0_00016 Key Byte 2 0x0_00027 Key Byte 3 0x0_00038 Key Byte 4 0x0_00049 Key Byte 5 0x0_0005A Key Byte 6 0x0_0006B Key Byte 7 0x0_0007After clearing CCIF to launch the Verify Backdoor Access Key command, the flashmemory 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 inFCCOB to the backdoor comparison key in the Flash Configuration Field. If thebackdoor keys match, the FSEC[SEC] field is changed to the unsecure state and securityis released. If the backdoor keys do not match, security is not released and all futureattempts to execute the Verify Backdoor Access Key command are immediately abortedand the FSTAT[ACCERR] bit is (again) set to 1 until a reset of the flash memory modulemodule occurs. If the entire 8-byte key is all zeros or all ones, the Verify BackdoorAccess Key command fails with an access error. The CCIF flag is set after the VerifyBackdoor Access Key operation completes.Table 27-49. Verify Backdoor Access Key Command Error HandlingError Condition Error BitThe supplied key is all-0s or all-Fs FSTAT[ACCERR]An incorrect backdoor key is supplied FSTAT[ACCERR]Table continues on the next page...Chapter 27 Flash Memory Module (FTFA)KL25 Sub-Family Reference Manual, Rev. 3, September 2012Freescale Semiconductor, Inc. 453
