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Chapter 30 Security (S12X9SECV2)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

1233

The meaning of the bits KEYEN[1:0] is shown in Table 30-2. Please refer to Section 30.1.5.1,

“Unsecuring the MCU Using the Backdoor Key Access” for more information.

The meaning of the security bits SEC[1:0] is shown in Table 30-3. 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”).

30.1.4

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 30-2. Backdoor Key Access Enable Bits

KEYEN[1:0]

Backdoor Key

Access Enabled

0 (disabled)

1 (enabled)

0 (disabled)

Table 30-3. Security Bits

SEC[1:0]

Security State

1 (secured)

0 (unsecured)

1 (secured)

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