mc9s12xd256 Freescale Semiconductor, Inc, mc9s12xd256 Datasheet - Page 1233

• Manufacturer Part Number: mc9s12xd256
• Description: Hcs12x Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

The meaning of the bits KEYEN[1:0] is shown in
“Unsecuring the MCU Using the Backdoor Key Access”
The meaning of the security bits SEC[1:0] is shown in
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’.
30.1.4
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:
Freescale Semiconductor
Operation of the Secured Microcontroller
Please refer to the Flash block guide (FTX) for actual security configuration
(in section “Flash Module Security”).
Table 30-2. Backdoor Key Access Enable Bits
KEYEN[1:0]
SEC[1:0]
00
01
10
11
00
01
10
11
MC9S12XDP512 Data Sheet, Rev. 2.17
Table 30-3. Security Bits
NOTE
Table
Table
30-2. Please refer to
for more information.
Access Enabled
Security State
0 (unsecured)
Backdoor Key
30-3. For security reasons, the state of device
1 (secured)
1 (secured)
1 (secured)
0 (disabled)
0 (disabled)
0 (disabled)
1 (enabled)
Section 30.1.5.1,
Chapter 30 Security (S12X9SECV2)
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