Datasheet

the flash and EEPROM memory, the FSEC[SEC] bits will be changed to unsecure the
MCU. Key values of 0x0000 and 0xFFFF are not permitted as backdoor keys. While the
Verify Backdoor Access Key command is active, flash memory and EEPROM memory
will not be available for read access and will return invalid data.
The user code stored in the flash memory must have a method of receiving the backdoor
keys from an external stimulus. This external stimulus would typically be through one of
the on-chip serial ports.
If the KEYEN[1:0] bits are in the enabled state, the MCU can be unsecured by the
backdoor key access sequence described below:
1. Follow the command sequence for the verify backdoor access key command as
explained in Verify backdoor access key command.
2. If the verify backdoor access key command is successful, the MCU is unsecured and
the FSEC[SEC] bits are forced to the unsecure state of 10.
The verify backdoor access key command is monitored by the memory controller and an
illegal key will prohibit future use of the verify backdoor access key command. A reset of
the MCU is the only method to re-enable the verify backdoor access key command. The
security as defined in the flash and EEPROM security byte (0xFF7F) is not changed by
using the verify backdoor access key command sequence. The backdoor keys stored in
addresses 0xFF70–0xFF77 are unaffected by the verify backdoor access key command
sequence. The verify backdoor access key command sequence has no effect on the
program and erase protections defined in the flash and EEPROM protection register,
FPORT.
After the backdoor keys have been correctly matched, the MCU will be unsecured. After
the MCU is unsecured, the sector containing the flash and EEPROM security byte can be
erased and the flash and EEPROM security byte can be reprogrammed to the unsecure
state, if desired. In the unsecure state, the user has full control of the contents of the
backdoor keys by programming addresses 0xFF70–0xFF77 in the flash configuration
field.
4.5.2.7.2 Unsecuring the MCU using BDM
A secured MCU can be unsecured by using the following method to erase the flash and
EEPROM memory:
1. Reset the MCU.
2. Set FCDIV register as described in Writing the FCLKDIV register.
Flash and EEPROM
MC9S08PA60 Reference Manual, Rev. 1, 9/2012
88 Freescale Semiconductor, Inc.