S12OSCV2D datasheet(69/126 Pages) FREESCALE

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MC9S12DJ64 Device User Guide — V01.17

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 or via a sequence of BDM commands. Unsecuring

is also possible via the Backdoor Key Access. Refer to Flash Block Guide for details.

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 User 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 User 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.

4.4.3 Wait

This mode is entered by executing the CPU WAI instruction. In this mode the CPU will not execute

instructions. The internal CPU signals (address and data bus) will be fully static. All peripherals stay

active. For further power consumption the peripherals can individually turn off their local clocks.

S12OSCV2D 数据表(PDF) 69 Page - Freescale Semiconductor, Inc