The MC9S12XD/XDG/XHZ family retains the low cost, power consumption, EMC and code-size
efficiency advantages currently associated with the MC9S12 products.
Based around S12X core, the MC912X family runs 16-bit wide accesses without wait states for all
peripherals and memories. The MC912X family also features a new flexible interrupt handler, 
which allows multilevel nested interrupts.
The MC912X family features the performance boosting XGATE co-processor. The XGATE is
programmable in "C" language and runs at twice the bus frequency of the S12. Its instruction set is
optimized for data movement, logic and bit manipulation instructions. Any peripheral module can be
serviced by the XGATE.
The MC912X family contains up to 512K bytes of Freescale Semiconductor's 
industry leading, full automotive qualified Split-Gate Flash memory, 
with 4K bytes of additional integrated data EEPROM and
up to 32K bytes of static RAM.

FSEC - Flash Security Register
bit 7: KEYEN - Enable backdoor key to security.
       1 = backdoor to Flash is enabled.
       0 = backdoor to Flash is disabled.

bits 1-0: SEC - bits define the security state of the device
       00,01,11 - secured
       10       - unsecured


For UNSECURE: 
1) erase EEPROM memory
2) erase FLASH memory 
3) Select "Boot" command  
3) Select "UNSECURE" command

