MC68HC908AT32 Datasheet, PDF (60/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Electrically Erasable Programmable ROM (EEPROM)
5.3.4 EEPROM Redundant Mode
To extend the EEPROM data retention, the array can be placed in redundant mode. In this mode, the first
256 bytes of user EEPROM array are mapped to the last 256 bytes. Reading, programming and erasing
of the first 256 EEPROM bytes will physically affect two bytes of EEPROM. Addressing the last 256 bytes
will not be recognized. Block protection still applies but EEBP3 and EEBP2 are meaningless.
NOTE
Programming the EEPROM in non-redundant mode and programming the
data to its corresponding location before entering redundant mode is
recommended.
The EEPROM non-volatile register (EENVR) contains configurations concerning block protection and
redundancy. EENVR is physically located on the bottom of the EEPROM array. The contents are
non-volatile and are not modified by reset. On reset, this special register loads the EEPROM configuration
into a corresponding volatile EEPROM array configuration register (EEACR). Thereafter, all reads to the
EENVR will reload EEACR.
The EEPROM configuration can be changed by programming/erasing the EENVR like a normal EEPROM
byte. The new array configuration will take effect with a system reset or a read of the EENVR.
5.3.5 MCU Configuration
The EEPROM non-volatile register (EENVR) also contains general-purpose bits which can be used to
enable/disable functions within the MCU which, for safety reasons, need to be controlled from non-volatile
memory. On reset, this special register loads the MCU configuration into the volatile EEPROM array
configuration register (EEACR). Thereafter, all reads to the EENVR will reload EEACR.
The MCU configuration can be changed by programming/erasing the EENVR like a normal EEPROM
byte. The new array configuration will take affect with a system reset or a read of the EENVR.
5.3.6 MC68HC908AT32 EEPROM Security
The MC68HC908AT32 has a special security option which prevents program/erase access to memory
locations $08F0 to $08FF. This security function is enabled by programming the CON0 bit in the EENVR
to 0.
NOTE
Once armed, the security is permanently enabled. As a consequence, all
functions in the EENVR will remain in the state they were in immediately
before the security was enabled.
Once the security is armed, bulk and block erase modes are disabled for all EEPROM locations.
Byte erasing can be used for all locations except $08F0 to $08FF. These protected locations can be read
as normal.
MC68HC908AT32 Data Sheet, Rev. 3.1
60
Freescale Semiconductor