Datasheet

Operating Modes
Security
MC9S12DP256 — Revision 1.1
Operating Modes
user memory from $FF00 to $FFFF is not in the map except through
serial BDM commands.
Security
The device will make available a security feature preventing the
unauthorized read and write of the memory contents. This feature
allows:
• Protection of the contents of FLASH,
• Protection of the contents of EEPROM,
• Operation in single-chip mode,
• Operation from external memory with internal FLASH and
EEPROM disabled.
The user must be reminded that part of the security must lie with the
user’s code. An extreme example would be user’s code that dumps the
contents of the internal program. This code would defeat the purpose of
security.
At the same time the user may also wish to put a “back door” in the user’s
program. An example of this is the user downloads a “key” through the
SCI which allows access to a programming routine that updates
parameters stored in EEPROM.
Operation
Securing the
Microcontroller
Once the user has programmed the FLASH and EEPROM (if desired),
the part can be secured by programming the security bits located in the
FLASH module. These non-volatile bits will keep the part secured
through resetting the part and through powering down the part.
The security byte resides in a portion of the Flash array.
Two bits are used for security. The state of the security bits and the
resulting state of security are shown in Table 15. Note that there are
three secured bit combinations and only one unsecured combination.
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
For More Information On This Product,
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