S9S12XS256J0CAL Datasheet, PDF (233/738 Pages) Freescale Semiconductor, Inc – Microcontrollers

Security (S12XS9SECV2)
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’.
Table 7-4. Security Bits
SEC[1:0]
00
01
10
11
Security State
1 (secured)
1 (secured)
0 (unsecured)
1 (secured)
NOTE
Please refer to the Flash block guide for actual security configuration (in
section “Flash Module Security”).
7.1.4 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:
S12XS Family Reference Manual, Rev. 1.13
Freescale Semiconductor
233