4.5.2.9.11 Verify backdoor access key command
The verify backdoor access key command will execute only if it is enabled by the
NVM_FSEC[KEYEN] bits. The verify backdoor access key command releases security
if user-supplied keys match those stored in the flash security bytes of the flash
configuration field. See
for details. The code that performs verifying backdoor
access command must be running from RAM or EEPROM.
Table 4-39. Verify backdoor access key command FCCOB requirements
CCOBIX[2:0]
NVM_FCCOBHI parameters
NVM_FCCOBLO parameters
000
0x0C
Not required
001
Key 0
010
Key 1
011
Key 2
100
Key 3
Upon clearing NVM_FSTAT[CCIF] to launch the verify backdoor access key command,
the memory controller will check the NVM_FSEC[KEYEN] bits to verify that this
command is enabled. If not enabled, the memory controller sets the
NVM_FSTAT[ACCERR] bit. If the command is enabled, the memory controller
compares the key provided in FCCOB to the backdoor comparison key in the flash
configuration field with Key 0 compared to 0xFF70, and so on. If the backdoor keys
match, security will be 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
aborted (set NVM_FSTAT[ACCERR]) until a reset occurs. The NVM_FSTAT[CCIF]
flag is set after the verify backdoor access key operation has completed.
Table 4-40. Verify backdoor access key command error handling
Register
Error bit
Error condition
NVM_FSTAT
ACCERR
Set if CCOBIX[2:0] ≠ 100 at command launch
Set if an incorrect backdoor key is supplied
Set if backdoor key access has not been enabled (KEYEN[1:0] ≠ 10
Set if the backdoor key has mismatched since the last reset
FPVIOL
None
MGSTAT1
None
MGSTAT0
None
Chapter 4 Memory map
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
NXP Semiconductors
81
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