FXTH870xD
Sensors
28
Freescale Semiconductor, Inc.
4.9.2
FLASH Options Register (FOPT and NVOPT)
During reset, the contents of the nonvolatile location NVOPT are copied from FLASH into FOPT. Bits 5 through 2 are not used
and always read 0. This register may be read at any time, but writes have no meaning or effect. To change the value in this
register, erase and reprogram the NVOPT location in FLASH memory as usual and then issue a new MCU reset.
4.9.3
FLASH Configuration Register (FCNFG)
Bits 7 through 5 can
be read or written at any time. Bits 4 through 0 always read 0 and cannot be written.
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7
6
5
4
3
2
1
0
R
KEYEN
FNORED
0
0
0
0
SEC01
SEC00
W
Reset:
This register is loaded from nonvolatile location NVOPT during reset.
= Reserved
Figure 13. FLASH Options Register (FOPT)
Table 12. FOPT Register Field Descriptions
Field
Description
7
KEYEN
Backdoor Key Mechanism Enable
— When this bit is 0, the backdoor key mechanism cannot be used to disengage security.
The backdoor key mechanism is accessible only from user (secured) firmware. BDM commands cannot be used to write key
comparison values that would unlock the backdoor key. For more detailed information about the backdoor key mechanism, refer
to
0
No backdoor key access allowed
1
If user firmware writes an 8-byte value that matches the nonvolatile backdoor key (NVBACKKEY through NV7
in that order), security is temporarily disengaged until the next MCU reset
6
FNORED
Vector Redirection Disable
— When this bit is 1, then vector redirection is disabled.
0
Vector redirection enabled
1
Vector redirection disabled
1:0
SEC0[1:0]
Security State Code
— This 2-bit field determines the security state of the MCU as shown in
Table 13
. When the MCU is
secure, the contents of RAM and FLASH memory cannot be accessed by instructions from any unsecured source including the
BACKGROUND DEBUG interface. For more detailed information about security, refer to
to 1:0 after successful backdoor key entry or a successful blank check of FLASH.
Table 13. Security States
SEC01:SEC00
Description
0:0
secure
0:1
secure
1:0
unsecured
1:1
secure
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7
6
5
4
3
2
1
0
R
0
0
KEYACC
0
0
0
0
0
W
Reset:
0
0
0
0
0
0
0
0
= Reserved
Figure 14. FLASH Configuration Register (FCNFG)
Содержание FXTH870 D Series
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