Register 24: EEPROM Unlock (EEUNLOCK), offset 0x020
The EEUNLOCK register can be used to unlock the whole EEPROM or a single block using a
password. Unlocking is only required if a password is registered using the EEPASSn registers for
the block that is selected by the EEBLOCK register. If block 0 has a password, it locks the remaining
blocks from any type of access, but uses its own protection mechanism, for example readable, but
not writable when locked. In addition, if block 0 has a password, it must be unlocked before unlocking
any other block.
The EEUNLOCK register is written between 1 and 3 times to form the 32-bit, 64-bit, or 96-bit
password registered using the EEPASSn registers. The value used to configure the EEPASS0
register must always be written last. For example, for a 96-bit password, the value used to configure
the EEPASS2 register must be written first followed by the EEPASS1 and EEPASS0 register values.
The block or the whole EEPROM can be re-locked by writing 0xFFFF.FFFF to this register.
In the event that an invalid value is written to this register, the block remains locked. The state of
the EEPROM lock can be determined by reading back the EEUNLOCK register. If a multi-word
password is set and the number of words written is incorrect, writing 0xFFFF.FFFF to this register
reverts the EEPROM lock to the locked state, and the proper unlock sequence can be retried.
Note that the internal logic is balanced to prevent any electrical or time-based attack being used to
find the correct password or its length.
Note: A read of the EEUNLOCK register during the EEPROM initialization sequence is only valid
when the WORKING bit is 0 in EEDONE register:
EEPROM Unlock (EEUNLOCK)
Base 0x400A.F000
Offset 0x020
Type RW, reset -
16171819202122232425262728293031
UNLOCK
RWRWRWRWRWRWRWRWRWRWRWRWRWRWRWRWType
----------------Reset
0123456789101112131415
UNLOCK
RWRWRWRWRWRWRWRWRWRWRWRWRWRWRWRWType
----------------Reset
DescriptionResetTypeNameBit/Field
EEPROM Unlock
DescriptionValue
The EEPROM is locked.0
The EEPROM is unlocked.1
The EEPROM is locked if the block referenced by the EEBLOCK register
has a password registered, or if the master block (block 0) has a
password. Unlocking is performed by writing the password to this
register. The block or the EEPROM stays unlocked until it is locked
again or until the next reset. It can be locked again by writing
0xFFFF.FFFF to this register.
-RWUNLOCK31:0
659June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller
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