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MCF51QE128 MCU Series Reference Manual, Rev. 3
Freescale Semiconductor 73
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Chapter 4 Memory
The FOPT register is loaded from the flash configuration field (see Section 4.2.1) during the reset
sequence, indicated by F in Figure 4-4.
The security feature in the flash module is described in Section 4.5.5, “Security”.
4.4.2.3 Flash Configuration Register (FCNFG)
The FCNFG register gates the security backdoor writes.
KEYACC is readable and writable while all remaining bits read 0 and are not writable. KEYACC is only
writable if KEYEN is set to the enabled state (see Section 4.4.2.2, “Flash Options Register (FOPT and
NVOPT)”).
NOTE
Flash array reads are allowed while KEYACC is set.
76543210
R KEYEN 0 0 0 0 SEC
W
ResetFF0000FF
Figure 4-4. Flash Options Register (FOPT)
Table 4-10. FOPT Field Descriptions
Field Description
7–6
KEYEN
Backdoor Key Security Enable Bits. The KEYEN[1:0] bits define the enabling of backdoor key access to the
flash module.
00 Disabled
01 Disabled (Preferred KEYEN state to disable Backdoor Key Access)
10 Enabled
11 Disabled
5–2 Reserved, should be cleared.
1–0
SEC
Flash Security Bits. The SEC[1:0] bits define the security state of the MCU. If the flash module is unsecured
using backdoor key access, the SEC[1:0] bits are forced to the unsecured state.
00 Unsecured
01 Unsecured
10 Secured
11 Unsecured
76543210
R0 0
KEYACC
00000
W
Reset00000000
Figure 4-5. Flash Configuration Register (FCNFG)