Datasheet

Flash EEPROM 256K
MC9S12DP256 — Revision 1.1
Flash EEPROM 256K
When KEYEN is set, the user can then bypass the security by:
1. Setting the KEYACC bit in the configuration (FCNFG) register.
2. Writing the correct four 16bit words to the flash using the backdoor
comparison keys addresses.
3. Clear the KEYACC bit.
4. If all four 16bit words match the flash content, the MCU is
unsecured by forcing the bits SEC[1:0] to the unsecure state.
5. If any of the four 16bit words does not match the flash content the
MCU remains secured and a security violation signal is sent to the
CPU.
The user has full control on those 4 words = 64 bits. The contents of the
flash is not changed by unsecuring the device. After the next reset
sequence the device is secured again unless the flash security byte was
changed by program or erase.
NV[6:2] — Non Volatile flag bits
These 5 bits are available to the user as non-volatile flags
SEC0[1:0] — memory security bits
Those two bits define the secure state of the device
For further details on the operation of a secured device see security
specification in section Operating Modes.
WARNING: If security is enabled then in order to perform product analysis
either it must be disabled by the backdoor key or the array must be
totally erased.
Table 30 Security States
SEC0[1:0] Description
00 secured
01 secured
10 unsecured
11 secured
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
nc...