ROHS MC9S08QE128 Reference Manual page 72

Chapter 4 Memory
All bits in the FOPT register are readable but are not writable. To change the value in this register, erase
and reprogram the NVOPT location in flash memory as usual and then issue an MCU reset.
The FOPT register is loaded from the flash location, NVOPT, during the reset sequence, indicated by F in
Figure 4-11.
Field
7:6 Backdoor Key Security Enable Bits — The KEYEN[1:0] bits define the enabling of backdoor key access to the
KEYEN[1:0] flash module as shown in
1:0 Flash Security Bits — The SEC[1:0] bits define the security state of the MCU as shown in
SEC[1:0] flash module is unsecured using backdoor key access, the SEC[1:0] bits are forced to the unsecured state.
The security feature in the flash module is described in
4.6.2.3 Flash Configuration Register (FCNFG)
The FCNFG register enables the flash interrupts and gates the security backdoor writes.
7
R 0
W
Reset 0
72
Table 4-13. FOPT Field Descriptions
Table 4-14.
Table 4-14. Flash KEYEN States
KEYEN[1:0]
00
1
01
10
11
1
Preferred KEYEN state to disable Backdoor Key Access.
Table 4-15. Flash Security States
SEC[1:0]
00
1
01
10
11
1
Preferred SEC state to set MCU to secured state.
6 5
0
KEYACC
0 0
= Unimplemented or Reserved
Figure 4-12. Flash Configuration Register (FCNFG)
MC9S08QE128 MCU Series Reference Manual, Rev. 2
Description
Status of Backdoor Key Access
DISABLED
DISABLED
ENABLED
DISABLED
Status of Security
SECURED
SECURED
UNSECURED
SECURED
Section 4.6.5, "Flash Module
4 3
0 0
0 0
Table 4-15. If the
Security".
2 1
0 0
0 0
Freescale Semiconductor
0
0
0