mc9s08gt32a Freescale Semiconductor, Inc, mc9s08gt32a Datasheet - Page 57

• Manufacturer Part Number: mc9s08gt32a
• Description: Hcs08 Microcontrollers 8-bit Microcontroller Family
• Manufacturer: Freescale Semiconductor, Inc

4.6.2
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.
Freescale Semiconductor
SEC0[1:0]
FNORED
Reset
KEYEN
Field
1:0
7
6
W
R
KEYEN
Flash Options Register (FOPT and NVOPT)
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
Vector Redirection Disable — When this bit is 1, vector redirection is disabled.
0 Vector redirection enabled.
1 Vector redirection disabled.
Security State Code — This 2-bit field determines the security state of the MCU as shown below. 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
Section 4.5,
00 Secure
01 Secure
10 Unsecured
11 Secure
SEC0[1:0] changes to 10 after successful backdoor key entry or a successful blank check of flash.
7
NVBACKKEY+7, in that order), security is temporarily disengaged until the next MCU reset.
= Unimplemented or Reserved
FNORED
“Security.”
6
This register is loaded from nonvolatile location NVOPT during reset.
Figure 4-5. Flash Options Register (FOPT)
Table 4-8. FOPT Field Descriptions
MC9S08GB60A Data Sheet, Rev. 1.02
0
5
0
4
Description
Section 4.5,
0
3
“Security.”
0
2
SEC01
1
Chapter 4 Memory
SEC00
0
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