MC9S12NE64CPVE Datasheet, PDF (61/554 Pages) Freescale Semiconductor, Inc – MC9S12NE64 Device Overview

1.4.2.2 Operation of the Secured Microcontroller
Low-Power Modes
1.4.2.2.1 Normal Single Chip Mode
This will be the most common usage of the secured MCU. Everything will appear the same as if the MCU
were not secured, with the exception of BDM operation. The BDM operation will be blocked.
1.4.2.2.2 Executing from External Memory
The user may wish to execute from external memory with a secured microcontroller. This is accomplished
by resetting directly into expanded mode. The internal FLASH will be disabled. BDM operations will be
blocked.
1.4.2.3 Unsecuring the Microcontroller
In order to unsecure the microcontroller, the internal FLASH must be erased. This can be performed
through an external program in expanded mode.
After the user has erased the FLASH, the MCU can be reset into special single chip mode. This invokes a
program that verifies the erasure of the internal FLASH. After this program completes, the user can erase
and program the FLASH security bits to the unsecured state. This is generally performed 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 MCU goes through a
reset before the security bits are reprogrammed to the unsecure state, the MCU will be secured again.
1.5 Low-Power Modes
The microcontroller features three main low-power modes. See the respective block description chapter
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 (CRG) block description chapter.
1.5.1 Stop
Executing the CPU STOP instruction stops all clocks and the oscillator thus putting the chip in fully static
mode. Wakeup from this mode can be performed via reset or external interrupts.
1.5.2 Pseudo Stop
This mode is entered by executing the CPU STOP instruction. In this mode, the oscillator stays 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 wakeup time from this mode
is significantly shorter.
MC9S12NE64 Data Sheet, Rev 1.0
Freescale Semiconductor
61