mc9s12e256 Freescale Semiconductor, Inc, mc9s12e256 Datasheet - Page 90

• Manufacturer Part Number: mc9s12e256
• Description: Hcs12 Microcontrollers 16-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 2 256 Kbyte Flash Module (FTS256K2V1)
2.3.2.2
The unbanked 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 $FF0F during the reset
sequence, indicated by F in
The security function in the Flash module is described in
90
KEYEN[1:0]
RNV[5:2]
SEC[1:0]
Reset
Field
1-0
5-2
1-0
W
R
Backdoor Key Security Enable Bits —The KEYEN[1:0] bits define the enabling of backdoor key access to the
Flash module as shown in
Reserved Nonvolatile Bits — The RNV[5:2] bits must remain in the erased 1 state for future enhancements.
Flash Security Bits — The SEC[1:0] bits define the security state of the MCU as shown in
module is unsecured using backdoor key access, the SEC bits are forced to 10.
Flash Security Register (FSEC)
F
7
KEYEN
= Unimplemented or Reserved
1
1
Preferred KEYEN state to disable Backdoor Key Access.
Preferred SEC state to set MCU to secured state.
6
F
Figure
KEYEN[1:0]
SEC[1:0]
Figure 2-5. Flash Security Register (FSEC)
01
01
00
10
11
00
10
11
1
1
Table
2-5.
Table 2-5. FSEC Field Descriptions
RNV5
Table 2-7. Flash Security States
MC9S12E256 Data Sheet, Rev. 1.08
Table 2-6. Flash KEYEN States
5
F
2-6.
RNV4
Status of Backdoor Key Access
F
4
Description
Status of Security
Section 2.6, “Flash Module
UNSECURED
DISABLED
DISABLED
DISABLED
ENABLED
SECURED
SECURED
SECURED
RNV3
F
3
RNV2
2
F
Freescale Semiconductor
Security”.
1
F
Table
SEC
2-7. If the Flash
0
F