The MC9S12Dxx microcontroller unit (MCU) is a 16-bit device composed
of standard on-chip peripherals including a 16-bit central processing
unit (HCS12 CPU), Flash EEPROM, RAM, EEPROM, two asynchronous serial 
communications interfaces (SCI), three serial peripheral interfaces
(SPI), an 8-channel IC/OC enhanced capture timer, two 8-channel,
10-bit analog-to-digital converters (ADC), an 8-channel pulse-width
modulator (PWM), a digital Byte Data Link Controller (BDLC), 29
discrete digital I/O channels (Port A, Port B, Port K and Port E), 20
discrete digital I/O lines with interrupt and wake up capability, five
CAN 2.0 A, B software compatible modules (MSCAN12), and an Inter-IC
Bus. The MC9S12DP512 has full 16-bit data paths throughout. However,
the external bus can operate in an 8-bit narrow mode so single 8-bit
wide memory can be interfaced for lower cost systems. The inclusion of
a PLL circuit allows power consumption and performance to be adjusted
to suit operational requirements.


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
