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Chapter 4 Memory

MC9S08SG8 MCU Series Data Sheet, Rev. 8

Freescale Semiconductor

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.

Table 4-7. FLASH Clock Divider Settings

fBus

PRDIV8

(Binary)

DIV

(Decimal)

fFCLK

Program/Erase Timing Pulse

s Min, 6.7s Max)

20 MHz

192.3 kHz

5.2

s

10 MHz

200 kHz

s

8 MHz

200 kHz

s

4 MHz

200 kHz

s

2 MHz

200 kHz

s

1 MHz

200 kHz

s

200 kHz

s

150 kHz

6.7

s

321

KEYEN

FNORED

—

SEC01

SEC00

Reset

This register is loaded from nonvolatile location NVOPT during reset.

= Unimplemented or Reserved

Figure 4-6. FLASH Options Register (FOPT)

Table 4-8. FOPT Register Field Descriptions

Field

Description

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.

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.”

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