AN2156 Freescale Semiconductor / Motorola, AN2156 Datasheet - Page 29

• Manufacturer Part Number: AN2156
• Description: Programming and Erasing FLASH and EEPROM Memories on the MC68HC908AS60A/AZ60A
• Manufacturer: Freescale Semiconductor / Motorola

EEPROM Block Protection and Security
AN2156
MOTOROLA
The MC68HC908AS60A/AZ60A has a special program/erase protection
feature which prevents program/erase access to certain memory
locations. This is called block protection and is controlled by the EEBPx
bits in the EExNVR registers.
There is also a special security feature of this EEPROM which
designates 16 bytes that can be permanently secured. These are in
addresses $06F0–$06FF and $08F0–$08FF. Once the EEPRTCT bit is
cleared for the first time, the values in these bytes are stored
permanently. They can be read, but not programmed or erased.
When the EEPRTCT bit is programmed to 0:
3. The calculated EExDIV value must be set in the EExDIVH and
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EExDIVL using one of two methods:
– Program the EExDIV value to EExDIVHNVR and
– Write the calculated EExDIV value to the EExDIVH and
Programming and erasing of secured locations (EEPROM-2:
$06F0–$06FF and EEPROM-1: $08F0–$08FF) are disabled
permanently.
The protected locations can be read as normal.
Programming and erasing of the EExNVR is disabled
permanently.
For unprotected locations (EEPROM-2: $0600–$06EF,
$0700–$07FF and EEPROM-1: $0800–$09EF, $0900–$09FF),
bulk and block erase modes are disabled. Single byte erase and
program modes are available. However, if the locations are
partially or entirely protected by EEPBx bits, the protected block
cannot be erased or programmed.
EExDIVLNVR and then reset the microcontroller. In this
method, the programmed value is loaded to the EExDIVH and
EExDIVL on reset.
EExDIVL. In this method, the written value is held in the
registers until the next reset occurs.
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EEPROM Block Protection and Security
Application Note
29