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Chapter 10 Security (S12X9SECV2)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 501
The meaning of the bits KEYEN[1:0] is shown in Table 10-2. Please refer to Section 10.1.5.1,
“Unsecuring the MCU Using the Backdoor Key Access” for more information.
The meaning of the security bits SEC[1:0] is shown in Table 10-3. For security reasons, the state of device
security is controlled by two bits. To put the device in unsecured mode, these bits must be programmed to
SEC[1:0] = ‘10’. All other combinations put the device in a secured mode. The recommended value to put
the device in secured state is the inverse of the unsecured state, i.e. SEC[1:0] = ‘01’.
NOTE
Please refer to the Flash block guide (FTX) for actual security configuration
(in section “Flash Module Security”).
10.1.4 Operation of the Secured Microcontroller
By securing the device, unauthorized access to the EEPROM and Flash memory contents can be prevented.
However, it must be understood that the security of the EEPROM and Flash memory contents also depends
on the design of the application program. For example, if the application has the capability of downloading
code through a serial port and then executing that code (e.g. an application containing bootloader code),
then this capability could potentially be used to read the EEPROM and Flash memory contents even when
the microcontroller is in the secure state. In this example, the security of the application could be enhanced
by requiring a challenge/response authentication before any code can be downloaded.
Secured operation has the following effects on the microcontroller:
Table 10-2. Backdoor Key Access Enable Bits
KEYEN[1:0]
Backdoor Key
Access Enabled
00 0 (disabled)
01 0 (disabled)
10 1 (enabled)
11 0 (disabled)
Table 10-3. Security Bits
SEC[1:0] Security State
00 1 (secured)
01 1 (secured)
10 0 (unsecured)
11 1 (secured)