MC9S08SH32 Datasheet, PDF (45/328 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 NVFTRIM
0xFFAF NVTRIM
0xFFB0 – NVBACKKEY
0xFFB7
0xFFB8 – Reserved
0xFFBB
0xFFBC
Reserved for stor-
age of 250 kHz
ICGTRM value
0xFFBD NVPROT
0xFFBE
Reserved for stor-
age of 243 kHz
ICGTRM value
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).
MC9S08SH32 Series Data Sheet, Rev. 2
Freescale Semiconductor
45
PRELIMINARY