Chapter 4 Memory
MC9S08QE128 MCU Series Reference Manual, Rev. 2
62
Freescale Semiconductor
Several reserved flash memory locations, shown in
, are used for storing values used by several
registers. 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 reserved
flash memory are transferred into corresponding FPROT and FOPT registers in the high-page registers
area to control security and block protection options.
The factory ICS trim value is stored in the flash information row (IFR
1
) and will be loaded into the
ICSTRM and ICSSC registers after any reset. The internal reference trim values stored in flash, TRIM and
FTRIM, can be programmed by third party programmers and must be copied into the corresponding ICS
registers by user code to override the factory trim.
NOTE
When the MCU is in active BDM, the trim value in the IFR will not be
loaded. Instead, the ICSTRM register will reset to 0x80 and the FTRIM bit
in the ICSSC register will be reset to 0.
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
0x187D
PTETOG
PTETOG7 PTETOG6 PTETOG5 PTETOG4 PTETOG3 PTETOG2 PTETOG1 PTETOG0
0x187E–
0x187F
Reserved
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
1. IFR — Nonvolatile information memory that can be only accessed during production test. During production test, system
initialization, configuration and test information is stored in the IFR. This information cannot be read or modified in normal user
or background debug modes.
Table 4-4. Reserved Flash Memory Addresses
Address
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
0xFFAE
Reserved for
Storage of FTRIM
0
0
0
0
0
0
0
FTRIM
0xFFAF
Reserved for
Storage of
ICSTRM
TRIM
0xFFB0 –
0xFFB7
NVBACKKEY
8-Byte Comparison Key
0xFFB8 –
0xFFBC
Reserved
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0xFFBD
NVPROT
FPS
FPOPEN
0xFFBE
Reserved
—
—
—
—
—
—
—
—
0xFFBF
NVOPT
KEYEN
0
0
0
0
SEC
Table 4-3. High-Page Register Summary (Sheet 4 of 4)
Address
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
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