NXP Semiconductors freescale semiconductor MC13211, Reference Manual

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MCU Memory
MC1321x Reference Manual, Rev. 1.6
11-8 Freescale Semiconductor
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 (SEC01:SEC00) to the unsecured state (1:0).
11.3 RAM
The HCS08 includes static RAM. The locations in RAM below 0x0100 can be accessed using the more
efficient direct addressing mode, and any single bit in this area can be accessed with the bit manipulation
instructions (BCLR, BSET, BRCLR, and BRSET). Locating the most frequently accessed program
variables in this area of RAM is preferred.
The RAM retains data when the MCU is in low-power wait, Stop2, or Stop3 Mode. At power-on or after
wake up from Stop1, 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.
For compatibility with older M68HC05 MCUs, the HCS08 resets the stack pointer to 0x00FF. In the
HCS08, it is usually best to re-initialize the stack pointer to the top of the RAM so the direct page RAM
can be used for frequently accessed RAM variables and bit-addressable program variables. Include the
following 2-instruction sequence in the reset initialization routine (where RamLast is equated to the
highest address of the RAM in the Freescale-provided equate file).
LDHX #1 ;point one past RAM
TXS ;SP<-(H:X-1)
When security is enabled, the RAM is considered a secure memory resource and is not accessible through
BDM or through code executing from non-secure memory. See
Section 11.5, “Security” for a detailed
description of the security feature.
Table 11-4. Nonvolatile Register Summary
Address Register Name Bit 7 6 5 4 3 2 1 Bit 0
0xFFB0
–
0xFFB7 NVBACKKEY
8-Byte Comparison Key
0xFFB8
–
0xFFBC Reserved
—
— —
— —
— —
— —
— —
— —
— —
—
0xFFBD NVPROT FPOPEN FPDIS FPS2 FPS1 FPS0 0 0 0
0xFFBE Reserved
1
1
This location is used to store the factory trim value for the ICG.
— — — — — — — —
0xFFBF NVOPT KEYEN FNORED 0 0 0 0 SEC01 SEC00