MC9S12A128 MOTOROLA [Motorola, Inc], MC9S12A128 Datasheet - Page 46

• Manufacturer Part Number: MC9S12A128
• Description: Microcontroller unit (MCU)
• Manufacturer: MOTOROLA [Motorola, Inc]

MC9S12A128 Device Guide — V01.01
as internal bus conflicts between BDM and the external master can cause improper operation of both
functions.
4.3 Security
The device will make available a security feature preventing the unauthorized read and write of the
memory contents. This feature allows:
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.
4.3.1 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.
Check the HCS12 128K Flash Block Guide (Motorola document order number, S12FTS128KV1/D) for
more details on the security configuration.
4.3.2 Operation of the Secured Microcontroller
4.3.2.1 Normal Single Chip Mode
This will be the most common usage of the secured part. Everything will appear the same as if the part was
not secured with the exception of BDM operation. The BDM operation will be blocked.
4.3.2.2 Executing from External Memory
The user may wish to execute from external space with a secured microcontroller. This is accomplished
by resetting directly into expanded mode. The internal FLASH and EEPROM will be disabled. BDM
operations will be blocked.
46
•
•
•
•
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.