NXP Semiconductors freescale semiconductor ColdFire MCF51CN128 Series, Справочное руководство

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Memory
MCF51CN128 Reference Manual, Rev. 6
4-26 Freescale Semiconductor
4.4.2.2 Flash Options Register (FOPT and NVOPT)
The FOPT register holds all bits associated with the security of the MCU and flash module. The FOPT
register is read only.
The FOPT register is loaded from the flash configuration field during the reset sequence, indicated by F in
Figure 4-5 .
The security feature in the flash module is described in Section 4.5, “Security .”
Table 4-8.
FCDIV Field Descriptions
Field Description
7
FDIVLD
Clock Divider Load Control . When writing to the FCDIV register for the first time after a reset, the value written
to this bit controls the future ability to write to the FCDIV register:
0 Locks the FCDIV register contents; all future writes to FCDIV are ignored.
1 Keeps the FCDIV register writable; next write to FCDIV is allowed.
When reading the FCDIV register, the value of the FDIVLD bit read indicates the following:
0 FCDIV register has not been written to since the last reset.
1 FCDIV register has been written to since the last reset.
6
PRDIV8
Enable Prescalar by 8
.
0 The bus clock is directly fed into the clock divider
.
1 The bus clock is divided by 8 before feeding into the clock divider.
5–0
FDIV
Clock Divider Bits . The combination of PRDIV8 and FDIV[5:0] must divide the bus clock to a frequency of
150 kHz–200 kHz. The minimum divide ratio is 2 (PRDIV8=0, FDIV=0x01) and the maximum divide ratio is 512
(PRDIV8=1, FDIV=0x3F).
7 6 5 4 3 2 1 0
R KEYEN 0 0 0 0 SEC
W
Reset F F 0 0 0 0 F F
Figure 4-5. Flash Options Register (FOPT)
Table 4-9.
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, must 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