MC9S08SG8 Datasheet, PDF (45/310 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 4 Memory
Nonvolatile FLASH registers, shown in Table 4-4, are located in the FLASH memory. These registers
include an 8-byte backdoor key, NVBACKKEY, which can be used to gain access to secure memory
resources. During reset events, the contents of NVPROT and NVOPT in the nonvolatile register area of the
FLASH memory are transferred into corresponding FPROT and FOPT working registers in the high-page
registers to control security and block protection options.
Table 4-4. Nonvolatile Register Summary
Address Register Name
0xFFAE Reserved for
storage of FTRIM
0xFFAF Reserved for
storage of ICSTRM
0xFFB0 – NVBACKKEY
0xFFB7
0xFFB8 – Reserved
0xFFBC
0xFFBD NVPROT
0xFFBE Reserved
0xFFBF NVOPT
Bit 7
0
—
—
—
KEYEN
6
0
—
—
—
FNORED
5
4
3
2
0
0
0
0
TRIM
8-Byte Comparison Key
—
—
—
—
—
—
—
—
FPS
—
—
—
—
0
0
0
0
1
Bit 0
0
FTRIM
—
—
—
—
FPDIS
—
—
SEC
Provided the key enable (KEYEN) bit is 1, the 8-byte comparison key can be used to temporarily
disengage memory security. This key mechanism can be accessed only through user code running in secure
memory. (A security key cannot be entered directly through background debug commands.) This security
key can be disabled completely by programming the KEYEN bit to 0. If the security key is disabled, the
only way to disengage security is by mass erasing the FLASH if needed (normally through the background
debug interface) and verifying that FLASH is blank. To avoid returning to secure mode after the next reset,
program the security bits (SEC) to the unsecured state (1:0).
MC9S08SG8 MCU Series Data Sheet, Rev. 0
Freescale Semiconductor
PRELIMINARY
45