TM4C1237E6PZ Datasheet, PDF (520/1306 Pages) Texas Instruments – Tiva Microcontroller

Internal Memory
Timing Considerations
After enabling or resetting the EEPROM module, software must wait until the WORKING bit in the
EEDONE register is clear before accessing any EEPROM registers.
In the event that there are Flash memory writes or erases and EEPROM writes active, it is possible
for the EEPROM process to be interrupted by the Flash memory write/erase and then continue after
the Flash memory write is completed. This action may change the amount of time that the EEPROM
operation takes.
EEPROM operations must be completed before entering Sleep or Deep-Sleep mode. Ensure the
EEPROM operations have completed by checking the EEPROM Done Status (EEDONE) register
before issuing a WFI instruction to enter Sleep or Deep-Sleep.
Reads of words within a block are at direct speed, which means that wait states are automatically
generated if the system clock is faster than the speed of the EEPROM. The read access time is
specified in Table 22-28 on page 1281.
Writing the EEOFFSET register also does not incur any penalties.
Writing the EEBLOCK register is not delayed, but any attempt to access data within that block is
delayed by 4 clocks after writing EEBLOCK. This time is used to load block specific information.
Writes to words within a block are delayed by a variable amount of time. The application may use
an interrupt to be notified when the write is done, or alternatively poll for the done status in the
EEDONE register. The variability ranges from the write timing of the EEPROM to the erase timing
of EEPROM, where the erase timing is less than the write timing of most external EEPROMs.
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. The locking behavior
is such that blocks 1 to 31 are inaccessible until block 0 is unlocked, and block 0 follows the rules
defined by its protection bits. 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 one to three times
to form the 32-bit, 64-bit, or 96-bit password registered using the EEPASSn register. 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 the EEPASS0 register values. 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 protection bits provide discrete control of read and write access for each block which allows
various protection models per block, including:
520
June 12, 2014
Texas Instruments-Production Data