NXP Semiconductors freescale semiconductor ColdFire MCF51CN128 Series, Reference Manual

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Memory
MCF51CN128 Reference Manual, Rev. 6
Freescale Semiconductor 4-23
The factory trim values are stored in the flash information row (IFR)
1
and are automatically loaded into
the MCGTRM and MCGSC registers after any reset. The oscillator trim values stored in TRIM and
FTRIM can be reprogrammed by third party programmers and must be copied into the corresponding
MCG registers (MCGTRM and MCGSC) by user code to override the factory trim.
NOTE
When the MCU is in active BDM, the trim value in the IFR is not loaded.
Instead, the MCGTRM register resets to 0x80 and MCGSC[FTRIM] resets
to zero.
Provided the key enable (KEYEN) bit is set, 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 clearing the KEYEN bit. If the security key is disabled, the only way
to disengage security is by mass-erasing the flash (normally through the background debug interface) and
verifying the flash is blank.
4.3 RAM
An MCF51CN128 series microcontroller includes up to 24 KB of static RAM. RAM is most efficiently
accessed using the A5-relative addressing mode (address register indirect with displacement mode). Any
single bit in this area can be accessed with the bit manipulation instructions (BCLR, BSET,etc.).
At power-on, the contents of RAM are uninitialized. RAM data is unaffected by any reset provided that
the supply voltage does not drop below the minimum value for RAM retention (V
RAM
).
Table 4-5. Reserved Flash Memory Addresses
Address Register 7 6 5 4 3 2 1 0
0x(00)00_03FC–
0x(00)00_03FD
Reserved
— — — — — — — —
0x(00)00_03FE Storage of
FTRIM
0 0 0 0 0 0 0 FTRIM
0x(00)00_03FF Storage of
MCGTRM
TRIM
0x(00)00_0400–
0x(00)00_0407
8-Byte Backdoor Comparison Key
0x(00)00_0408–
0x(00)00_040C
Reserved
— — — — — — — —
0x(00)00_040D NVPROT FPS FPOPEN
0x(00)00_040E Reserved — — — — — — — —
0x(00)00_040F NVOPT KEYEN 0 0 0 0 SEC
1. IFR — Nonvolatile information memory that can only be 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.