MC9S12K Datasheet, PDF (74/126 Pages) Freescale Semiconductor, Inc – Microcontrollers

Device User Guide — 9S12KT256DGV1/D V01.09
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.
4.3.3 Unsecuring the Microcontroller
In order to unsecure the microcontroller, the internal FLASH and EEPROM must be erased. This can be
done through an external program in expanded mode.
Once the user has erased the FLASH and EEPROM, the part can be reset into special single chip mode.
This invokes a program that verifies the erasure of the internal FLASH and EEPROM. Once this program
completes, the user can erase and program the FLASH security bits to the unsecured state. This is generally
done through the BDM, but the user could also change to expanded mode (by writing the mode bits
through the BDM) and jumping to an external program (again through BDM commands). Note that if the
part goes through a reset before the security bits are reprogrammed to the unsecure state, the part will be
secured again.
4.4 Low Power Modes
The microcontroller features three main low power modes. Consult the respective Block Guide for
information on the module behavior in Stop, Pseudo Stop, and Wait Mode. An important source of
information about the clock system is the Clock and Reset Generator Guide (CRG).
4.4.1 Stop
Executing the CPU STOP instruction stops all clocks and the oscillator thus putting the chip in fully static
mode. Wake up from this mode can be done via reset or external interrupts.
4.4.2 Pseudo Stop
This mode is entered by executing the CPU STOP instruction. In this mode the oscillator is still running
and the Real Time Interrupt (RTI) or Watchdog (COP) sub module can stay active. Other peripherals are
turned off. This mode consumes more current than the full STOP mode, but the wake up time from this
mode is significantly shorter.
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