MC9S08RG60 Datasheet, PDF (41/232 Pages) Motorola, Inc – Microcontrollers

SoC Guide — MC9S08RG60/D Rev 1.10
Nonvolatile FLASH registers, shown in Table 4-4, are located in the FLASH memory. These registers
include an 8-byte backdoor key that optionally 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.
Address
$FFB0–
$FFB7
$FFB8–
$FFBC
$FFBD
$FFBE
$FFBF
Register Name
NVBACKKEY
Reserved
NVPROT
Reserved
NVOPT
Table 4-4 Nonvolatile Register Summary
Bit 7
6
5
4
3
2
8-Byte Comparison Key
—
—
—
—
—
—
—
—
—
—
—
—
FPOPEN FPDIS FPS2
FPS1
FPS0
0
—
—
—
—
—
—
KEYEN FNORED
0
0
0
0
1
Bit 0
—
—
0
—
SEC01
—
—
0
—
SEC00
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).
4.3 RAM
The MC9S08RC/RD/RE/RG includes static RAM. The locations in RAM below $0100 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
wakeup 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 $00FF. In the
MC9S08RC/RD/RE/RG, it is usually best to reinitialize 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 your reset initialization routine (where RamLast
is equated to the highest address of the RAM in the Freescale-provided equate file).
LDHX
TXS
#RamLast+1
;point one past RAM
;SP<-(H:X-1)
Freescale Semiconductor
MC9S08RC/RD/RE/RG
41