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512 Kbyte Flash Module (S12XFTX512K4V2)
BookTitle, Rev. 2.4
Freescale Semiconductor 109
2.3.2.2 Flash Security Register (FSEC)
The FSEC register holds all bits associated with the security of the MCU and Flash module.
All bits in the FSEC register are readable but are not writable.
The FSEC register is loaded from the Flash Configuration Field at address 0x7F_FF0F during the reset
sequence, indicated by F in Figure 2-5.
The security function in the Flash module is described in Section 2.6, “Flash Module Security”.
Module Base + 0x0001
76543210
R KEYEN RNV5 RNV4 RNV3 RNV2 SEC
W
Reset F F F FFFFF
= Unimplemented or Reserved
Figure 2-5. Flash Security Register (FSEC)
Table 2-4. FSEC Field Descriptions
Field Description
7-6
KEYEN[1:0]
Backdoor Key Security Enable Bits — The KEYEN[1:0] bits define the enabling of backdoor key access to the
Flash module as shown in Table 2-5.
5-2
RNV[5:2]
Reserved Nonvolatile Bits — The RNV[5:2] bits should remain in the erased state for future enhancements.
1-0
SEC[1:0]
Flash Security Bits — The SEC[1:0] bits define the security state of the MCU as shown in Table 2-6. If the Flash
module is unsecured using backdoor key access, the SEC[1:0] bits are forced to 1:0.
Table 2-5. Flash KEYEN States
KEYEN[1:0] Status of Backdoor Key Access
00 DISABLED
01
1
1 Preferred KEYEN state to disable Backdoor Key Access.
DISABLED
10 ENABLED
11 DISABLED
Table 2-6. Flash Security States
SEC[1:0] Status of Security
00 SECURED
01
1
1 Preferred SEC state to set MCU to secured state.
SECURED
10 UNSECURED
11 SECURED