Datasheet

Note: The associated Flash and EEPROM fields in the MEMTIM0 register must be programmed
to the same values. For example, the FWS field must be programmed to the same value as
the EWS field.
Locking and Passwords
The EEPROM can be locked at both the module level and the block level. The lock is controlled by
a password that is stored in the EEPROM Password (EEPASSn) registers and can be any 32-bit
to 96-bit value other than all 1s. Block 0 is the master block, the password for block 0 protects the
control registers as well as all other blocks. Each block can be further protected with a password
for that block.
If a password is registered for block 0, then the whole module is locked at reset. As a result, the
EEBLOCK register cannot be changed from 0 until block 0 is unlocked.
A password registered with any block, including block 0, allows for protection rules that control
access of that block based on whether it is locked or unlocked. Generally, the lock can be used to
prevent write accesses when locked or can prevent read and write accesses when locked.
All password protected blocks are locked at reset. To unlock a block, the correct password value
must be written to the EEPROM Unlock (EEUNLOCK) register by writing to it once, twice, or three
times, depending on the size of the password. A block or the module may be re-locked by writing
0xFFFF.FFFF to the EEUNLOCK register because 0xFFFF.FFFF is not a valid password.
Protection and Access Control
The PROT protection field in the EEPROM Protection (EEPROT) register provides discrete control
of read and write access for each block which allows various protection models per block. The
protection configurations allowed are as follows:
■ PROT = 0x0
– Without password: Readable and writable at any time. This mode is the default when there
is no password.
– With password: Readable, but only writable when unlocked by the password. This mode is
the default when there is a password.
■ PROT = 0x1
– With password: Readable or writable only when unlocked.
– This value has no meaning when there is no password.
■ PROT = 0x2
– Without password: Readable but not writable.
– With password: Readable only when unlocked, not writable under any conditions.
Additionally, access protection may be applied based on the processor mode. This configuration
allows for supervisor-only access or supervisor and user access, which is the default. Supervisor-only
access mode also prevents access by the µDMA and Debugger.
Additionally, the master block may be used to control access protection for the protection mechanism
itself. If access control for block 0 is for supervisor only, then the whole module may only be accessed
in supervisor mode.
647December 13, 2013
Texas Instruments-Advance Information
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TM4C129XNCZAD Microcontroller