S9S08AW16A FREESCALE [Freescale Semiconductor, Inc], S9S08AW16A Datasheet - Page 49

• Manufacturer Part Number: S9S08AW16A
• Description: HCS08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

0xFFB0 –
0xFFB7
0xFFB8 –
0xFFBB
0xFFBC
0xFFBD
0xFFBE
0xFFBF
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
The MC9S08AC16 Series 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, 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
MC9S08AC16 Series, 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 your reset initialization routine (where RamLast is equated
to the highest address of the RAM in the Freescale-provided equate file).
Freescale Semiconductor
Address
NVBACKKEY
Reserved
Reserved for stor-
age of 250 kHz
ICGTRM value
NVPROT
Reserved for stor-
age of 243 kHz
ICGTRM value
NVOPT
RAM
Register Name
LDHX
TXS
#RamLast+1
KEYEN
FPS7
Bit 7
—
—
—
—
Table 4-4. Nonvolatile Register Summary
MC9S08AC16 Series Data Sheet, Rev. 8
FNORED
FPS6
—
—
—
—
6
;point one past RAM
;SP<-(H:X-1)
FPS5
—
—
—
—
5
0
8-Byte Comparison Key
FPS4
—
—
—
—
4
0
FPS3
—
—
—
—
3
0
FPS2
—
—
—
—
2
0
SEC01
FPS1
—
—
—
—
1
Chapter 4 Memory
SEC00
FPDIS
Bit 0
—
—
—
—
49