MC9S08SG8 Datasheet, PDF (55/310 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 4 Memory
Table 4-7. FLASH Clock Divider Settings
f_Bus
20 MHz
10 MHz
8 MHz
4 MHz
2 MHz
1 MHz
200 kHz
150 kHz
PRDIV8
(Binary)
1
0
0
0
0
0
0
0
DIV
(Decimal)
12
49
39
19
9
4
0
0
f_FCLK
192.3 kHz
200 kHz
200 kHz
200 kHz
200 kHz
200 kHz
200 kHz
150 kHz
Program/Erase Timing Pulse
(5 µs Min, 6.7 µs Max)
5.2 µs
5 µs
5 µs
5 µs
5 µs
5 µs
5 µs
6.7 µs
4.7.2 FLASH Options Register (FOPT and NVOPT)
During reset, the contents of the nonvolatile location NVOPT are copied from FLASH into FOPT. 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.
R
W
Reset
7
KEYEN
6
5
4
3
2
1
FNORED
0
0
0
0
SEC01
This register is loaded from nonvolatile location NVOPT during reset.
= Unimplemented or Reserved
Figure 4-6. FLASH Options Register (FOPT)
0
SEC00
Table 4-8. 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 Section 4.6, “Security.”
0 No backdoor key access allowed.
1 If user firmware writes an 8-byte value that matches the nonvolatile backdoor key (NVBACKKEY through
NVBACKKEY+7 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 4-9. 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. SEC01:SEC00 changes to 1:0 after successful
backdoor key entry or a successful blank check of FLASH.
For more detailed information about security, refer to Section 4.6, “Security.”
MC9S08SG8 MCU Series Data Sheet, Rev. 0
Freescale Semiconductor
PRELIMINARY
55