Security (S12XS9SECV2)
MC9S12G Family Reference Manual Rev.1.27
348 NXP Semiconductors
9.1.3 Securing the Microcontroller
Once the user has programmed the Flash and EEPROM, the chip can be secured by programming the
security bits located in the options/security byte in the Flash memory array. These non-volatile bits will
keep the device secured through reset and power-down.
The options/security byte is located at address 0xFF0F (= global address 0x7F_FF0F) in the Flash memory
array. This byte can be erased and programmed like any other Flash location. Two bits of this byte are used
for security (SEC[1:0]). On devices which have a memory page window, the Flash options/security byte
is also available at address 0xBF0F by selecting page 0x3F with the PPAGE register. The contents of this
byte are copied into the Flash security register (FSEC) during a reset sequence.
The meaning of the bits KEYEN[1:0] is shown in Table 9-3. Please refer to Section 9.1.5.1, “Unsecuring
the MCU Using the Backdoor Key Access” for more information.
The meaning of the security bits SEC[1:0] is shown in Table 9-4. 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’.
EEPROM Array Access
?? ??
NVM Commands
?
1
? ?
1
?
1
BDM
??
—
?
2
DBG Module Trace
??
——
1
Restricted NVM command set only. Please refer to the NVM wrapper block guides for detailed information.
2
BDM hardware commands restricted to peripheral registers only.
76543210
0xFF0F KEYEN1 KEYEN0 NV5 NV4 NV3 NV2 SEC1 SEC0
Figure 9-1. Flash Options/Security Byte
Table 9-3. 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 9-2. Feature Availability in Unsecure and Secure Modes on S12XS
Unsecure Mode Secure Mode
NS SS NX ES EX ST NS SS NX ES EX ST
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