mc9s08gt16a Freescale Semiconductor, Inc, mc9s08gt16a Datasheet - Page 57

• Manufacturer Part Number: mc9s08gt16a
• 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
Reset
KEYEN
Field
7
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
7
200 kHz
150 kHz
20 MHz
10 MHz
8 MHz
4 MHz
2 MHz
1 MHz
NVBACKKEY+7, in that order), security is temporarily disengaged until the next MCU reset.
f
Bus
= Unimplemented or Reserved
FNORED
(Binary)
PRDIV8
6
1
0
0
0
0
0
0
0
This register is loaded from nonvolatile location NVOPT during reset.
Figure 4-6. FLASH Options Register (FOPT)
Table 4-7. FLASH Clock Divider Settings
MC9S08GT16A/GT8A Data Sheet, Rev. 1
Table 4-8. FOPT Field Descriptions
DIV5:DIV0
(Decimal)
0
5
12
49
39
19
9
4
0
0
0
4
192.3 kHz
200 kHz
200 kHz
200 kHz
200 kHz
200 kHz
200 kHz
150 kHz
f
FCLK
Description
Section 4.5,
0
3
Program/Erase Timing Pulse
(5 µs Min, 6.7 µs Max)
“Security.”
5.2 µs
6.7 µs
5 µs
5 µs
5 µs
5 µs
5 µs
5 µs
0
2
SEC01
1
SEC00
Memory
0
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