ROHS MC9S08QE128 - Page 72

Chapter 4 Memory
MC9S08QE128 MCU Series Reference Manual, Rev. 2
72 Freescale Semiconductor
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.
The security feature in the flash module is described in Section 4.6.5, “Flash Module Security”.
4.6.2.3 Flash Configuration Register (FCNFG)
The FCNFG register enables the flash interrupts and gates the security backdoor writes.
Table 4-13. FOPT 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 4-14.
1:0
SEC[1:0]
Flash Security Bits — The SEC[1:0] bits define the security state of the MCU as shown in Table 4-15. If the
flash module is unsecured using backdoor key access, the SEC[1:0] bits are forced to the unsecured state.
Table 4-14. 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 4-15. 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
76543210
R0 0
KEYACC
00000
W
Reset 00000000
= Unimplemented or Reserved
Figure 4-12. Flash Configuration Register (FCNFG)