MC68HC08AS20 Datasheet, PDF (65/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

6.4.4 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 ($0800–$08FF) 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: Before entering redundant mode, program the EEPROM in
nonredundant mode.
6.4.5 EEPROM Configuration
The EEPROM nonvolatile register (EENVR) contains configurations
concerning block protection and redundancy. EENVR is physically
located on the bottom of the EEPROM array. The contents are
nonvolatile 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.
MC68HC08AS20 — Rev. 4.1
Freescale Semiconductor
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